cairnlang-core 0.5.0

//! The standard library — written *in Cairn*, authored through the one
//! Core API, exactly like the Tier-2 web framework.
//!
//! These are the generic higher-order list functions every real language
//! has (`map`/`filter`/`fold`). They exist here, in Cairn, only because
//! the language now has the two things that make them expressible: real
//! generics and first-class functions/closures. Before the keystone, code
//! that needed them hand-rolled a bespoke index recursion every time (see
//! the framework's old `render_kids`); now it passes a closure.
//!
//! Each public function is a thin entry over an index-recursive `_at`
//! helper — there is no drop-first list primitive, so iteration is by
//! index. All are pure: the closure's `Fn` type carries no effects (an
//! effect-polymorphic stdlib would need effect rows — out of scope, a
//! documented v0.4 boundary). Calls among them resolve when an app
//! assembles its module; the content-addressed store dedups them.

use crate::edit::{ExprSpec, FunctionSpec, StepSpec};
use crate::node::{BinOp, Param, Produces};
use crate::ty::{Confidence, Type};
use std::collections::BTreeSet;

fn r(n: &str) -> ExprSpec {
    ExprSpec::Ref(n.into())
}
fn num(n: i64) -> ExprSpec {
    ExprSpec::Lit(n)
}
fn add1(e: ExprSpec) -> ExprSpec {
    ExprSpec::BinOp {
        op: BinOp::Add,
        lhs: Box::new(e),
        rhs: Box::new(num(1)),
    }
}
fn eq(a: ExprSpec, b: ExprSpec) -> ExprSpec {
    ExprSpec::BinOp {
        op: BinOp::Eq,
        lhs: Box::new(a),
        rhs: Box::new(b),
    }
}
fn call(f: &str, args: Vec<ExprSpec>) -> ExprSpec {
    ExprSpec::Call {
        func: f.into(),
        args,
    }
}
fn callv(callee: ExprSpec, args: Vec<ExprSpec>) -> ExprSpec {
    ExprSpec::CallValue {
        callee: Box::new(callee),
        args,
    }
}
fn iff(c: ExprSpec, t: ExprSpec, e: ExprSpec) -> ExprSpec {
    ExprSpec::If {
        cond: Box::new(c),
        then_branch: Box::new(t),
        else_branch: Box::new(e),
    }
}
fn lget(list: ExprSpec, index: ExprSpec) -> ExprSpec {
    ExprSpec::ListGet {
        list: Box::new(list),
        index: Box::new(index),
    }
}
fn llen(e: ExprSpec) -> ExprSpec {
    ExprSpec::ListLen(Box::new(e))
}
fn cons(head: ExprSpec, tail: ExprSpec) -> ExprSpec {
    ExprSpec::ListCons {
        head: Box::new(head),
        tail: Box::new(tail),
    }
}
fn empty(elem: Type) -> ExprSpec {
    ExprSpec::ListEmpty { elem }
}
fn boolean(b: bool) -> ExprSpec {
    ExprSpec::Bool(b)
}
fn some(v: ExprSpec) -> ExprSpec {
    ExprSpec::OptionSome(Box::new(v))
}
fn none(elem: Type) -> ExprSpec {
    ExprSpec::OptionNone { elem }
}
fn p(name: &str, ty: Type) -> Param {
    Param {
        name: name.into(),
        ty,
        min_confidence: Confidence::External,
    }
}
fn ext(ty: Type) -> Produces {
    Produces {
        ty,
        confidence: Confidence::External,
    }
}
fn step(b: &str, v: ExprSpec) -> StepSpec {
    StepSpec {
        binding: b.into(),
        value: v,
    }
}
fn var(n: &str) -> Type {
    Type::Var(n.into())
}
fn list(t: Type) -> Type {
    Type::List(Box::new(t))
}
/// A pure function type `Fn(params) -> ret`.
fn fnt(params: Vec<Type>, ret: Type) -> Type {
    Type::Fn {
        params,
        ret: Box::new(ret),
        effects: BTreeSet::new(),
    }
}
fn tp(names: &[&str]) -> Vec<String> {
    names.iter().map(|s| (*s).to_string()).collect()
}

/// `map`, `filter`, `fold` (each with its index-recursive `_at` helper).
pub fn list_functions() -> Vec<FunctionSpec> {
    // fold_at<T,A>(f, acc, xs, i) = if i == len(xs) then acc
    //   else fold_at(f, f(acc, xs[i]), xs, i + 1)
    let fold_at = FunctionSpec {
        name: "fold_at".into(),
        type_params: tp(&["T", "A"]),
        params: vec![
            p("f", fnt(vec![var("A"), var("T")], var("A"))),
            p("acc", var("A")),
            p("xs", list(var("T"))),
            p("i", Type::Number),
        ],
        produces: ext(var("A")),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            eq(r("i"), r("n")),
            r("acc"),
            call(
                "fold_at",
                vec![
                    r("f"),
                    callv(r("f"), vec![r("acc"), lget(r("xs"), r("i"))]),
                    r("xs"),
                    add1(r("i")),
                ],
            ),
        ),
    };
    let fold = FunctionSpec {
        name: "fold".into(),
        type_params: tp(&["T", "A"]),
        params: vec![
            p("f", fnt(vec![var("A"), var("T")], var("A"))),
            p("acc", var("A")),
            p("xs", list(var("T"))),
        ],
        produces: ext(var("A")),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("fold_at", vec![r("f"), r("acc"), r("xs"), num(0)]),
    };

    // map_at<T,U>(f, xs, i) = if i == len(xs) then []
    //   else cons(f(xs[i]), map_at(f, xs, i + 1))
    let map_at = FunctionSpec {
        name: "map_at".into(),
        type_params: tp(&["T", "U"]),
        params: vec![
            p("f", fnt(vec![var("T")], var("U"))),
            p("xs", list(var("T"))),
            p("i", Type::Number),
        ],
        produces: ext(list(var("U"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            eq(r("i"), r("n")),
            empty(var("U")),
            cons(
                callv(r("f"), vec![lget(r("xs"), r("i"))]),
                call("map_at", vec![r("f"), r("xs"), add1(r("i"))]),
            ),
        ),
    };
    let map = FunctionSpec {
        name: "map".into(),
        type_params: tp(&["T", "U"]),
        params: vec![
            p("f", fnt(vec![var("T")], var("U"))),
            p("xs", list(var("T"))),
        ],
        produces: ext(list(var("U"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("map_at", vec![r("f"), r("xs"), num(0)]),
    };

    // filter_at<T>(f, xs, i) = if i == len(xs) then []
    //   else if f(xs[i]) then cons(xs[i], rest) else rest
    let filter_at = FunctionSpec {
        name: "filter_at".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("f", fnt(vec![var("T")], Type::Bool)),
            p("xs", list(var("T"))),
            p("i", Type::Number),
        ],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            eq(r("i"), r("n")),
            empty(var("T")),
            iff(
                callv(r("f"), vec![lget(r("xs"), r("i"))]),
                cons(
                    lget(r("xs"), r("i")),
                    call("filter_at", vec![r("f"), r("xs"), add1(r("i"))]),
                ),
                call("filter_at", vec![r("f"), r("xs"), add1(r("i"))]),
            ),
        ),
    };
    let filter = FunctionSpec {
        name: "filter".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("f", fnt(vec![var("T")], Type::Bool)),
            p("xs", list(var("T"))),
        ],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("filter_at", vec![r("f"), r("xs"), num(0)]),
    };

    // range_at(lo, hi) = if lo == hi then [] else cons(lo, range_at(lo+1, hi))
    let range_at = FunctionSpec {
        name: "range_at".into(),
        type_params: vec![],
        params: vec![p("lo", Type::Number), p("hi", Type::Number)],
        produces: ext(list(Type::Number)),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: iff(
            eq(r("lo"), r("hi")),
            empty(Type::Number),
            cons(
                r("lo"),
                call("range_at", vec![add1(r("lo")), r("hi")]),
            ),
        ),
    };
    let range = FunctionSpec {
        name: "range".into(),
        type_params: vec![],
        params: vec![p("lo", Type::Number), p("hi", Type::Number)],
        produces: ext(list(Type::Number)),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("range_at", vec![r("lo"), r("hi")]),
    };

    // any_at<T>(f, xs, i) = if i==len then false
    //   else if f(xs[i]) then true else any_at(f, xs, i+1)
    let any_at = FunctionSpec {
        name: "any_at".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("f", fnt(vec![var("T")], Type::Bool)),
            p("xs", list(var("T"))),
            p("i", Type::Number),
        ],
        produces: ext(Type::Bool),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            eq(r("i"), r("n")),
            boolean(false),
            iff(
                callv(r("f"), vec![lget(r("xs"), r("i"))]),
                boolean(true),
                call("any_at", vec![r("f"), r("xs"), add1(r("i"))]),
            ),
        ),
    };
    let any = FunctionSpec {
        name: "any".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("f", fnt(vec![var("T")], Type::Bool)),
            p("xs", list(var("T"))),
        ],
        produces: ext(Type::Bool),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("any_at", vec![r("f"), r("xs"), num(0)]),
    };

    // all_at<T>(f, xs, i) = if i==len then true
    //   else if f(xs[i]) then all_at(f, xs, i+1) else false
    let all_at = FunctionSpec {
        name: "all_at".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("f", fnt(vec![var("T")], Type::Bool)),
            p("xs", list(var("T"))),
            p("i", Type::Number),
        ],
        produces: ext(Type::Bool),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            eq(r("i"), r("n")),
            boolean(true),
            iff(
                callv(r("f"), vec![lget(r("xs"), r("i"))]),
                call("all_at", vec![r("f"), r("xs"), add1(r("i"))]),
                boolean(false),
            ),
        ),
    };
    let all = FunctionSpec {
        name: "all".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("f", fnt(vec![var("T")], Type::Bool)),
            p("xs", list(var("T"))),
        ],
        produces: ext(Type::Bool),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("all_at", vec![r("f"), r("xs"), num(0)]),
    };

    // find_at<T>(f, xs, i) = if i==len then None
    //   else if f(xs[i]) then Some(xs[i]) else find_at(f, xs, i+1)
    let find_at = FunctionSpec {
        name: "find_at".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("f", fnt(vec![var("T")], Type::Bool)),
            p("xs", list(var("T"))),
            p("i", Type::Number),
        ],
        produces: ext(Type::Option(Box::new(var("T")))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            eq(r("i"), r("n")),
            none(var("T")),
            iff(
                callv(r("f"), vec![lget(r("xs"), r("i"))]),
                some(lget(r("xs"), r("i"))),
                call("find_at", vec![r("f"), r("xs"), add1(r("i"))]),
            ),
        ),
    };
    let find = FunctionSpec {
        name: "find".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("f", fnt(vec![var("T")], Type::Bool)),
            p("xs", list(var("T"))),
        ],
        produces: ext(Type::Option(Box::new(var("T")))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("find_at", vec![r("f"), r("xs"), num(0)]),
    };

    // concat_at<T>(a, b, i) = if i == len(a) then b
    //   else cons(a[i], concat_at(a, b, i + 1))   — a ++ b, in order.
    let concat_at = FunctionSpec {
        name: "concat_at".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("a", list(var("T"))),
            p("b", list(var("T"))),
            p("i", Type::Number),
        ],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("a")))],
        result: iff(
            eq(r("i"), r("n")),
            r("b"),
            cons(
                lget(r("a"), r("i")),
                call("concat_at", vec![r("a"), r("b"), add1(r("i"))]),
            ),
        ),
    };
    let concat = FunctionSpec {
        name: "concat".into(),
        type_params: tp(&["T"]),
        params: vec![p("a", list(var("T"))), p("b", list(var("T")))],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("concat_at", vec![r("a"), r("b"), num(0)]),
    };

    // lpad0(s, w) = while len(s) < w: s = "0" ++ s
    let s_str = || ExprSpec::Str("0".into());
    let strlen = |e: ExprSpec| ExprSpec::StrLen(Box::new(e));
    let scat = |a: ExprSpec, b: ExprSpec| {
        ExprSpec::StrConcat(Box::new(a), Box::new(b))
    };
    let n2s = |e: ExprSpec| ExprSpec::NumberToStr(Box::new(e));
    let bop = |op: BinOp, a: ExprSpec, b: ExprSpec| ExprSpec::BinOp {
        op,
        lhs: Box::new(a),
        rhs: Box::new(b),
    };
    let lpad0 = FunctionSpec {
        name: "lpad0".into(),
        type_params: vec![],
        params: vec![p("s", Type::String), p("w", Type::Number)],
        produces: ext(Type::String),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("ls", strlen(r("s")))],
        result: iff(
            bop(BinOp::Ge, r("ls"), r("w")),
            r("s"),
            call("lpad0", vec![scat(s_str(), r("s")), r("w")]),
        ),
    };
    // decimal_to_str(d): "[-]W.FFFF" from the scaled mantissa. Reuses
    // the now-full-range num_to_str. (Magnitude negation overflows only
    // at Decimal i64::MIN — a ~9e14 value, the same documented edge as
    // every other magnitude op.)
    let decimal_to_str = FunctionSpec {
        name: "decimal_to_str".into(),
        type_params: vec![],
        params: vec![p("d", Type::Decimal)],
        produces: ext(Type::String),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![
            step("raw", ExprSpec::DecimalRaw(Box::new(r("d")))),
            step(
                "m",
                iff(
                    bop(BinOp::Lt, r("raw"), num(0)),
                    bop(BinOp::Sub, num(0), r("raw")),
                    r("raw"),
                ),
            ),
            step("whole", bop(BinOp::Div, r("m"), num(10_000))),
            step("frac", bop(BinOp::Mod, r("m"), num(10_000))),
        ],
        result: scat(
            scat(
                scat(
                    iff(
                        bop(BinOp::Lt, r("raw"), num(0)),
                        ExprSpec::Str("-".into()),
                        ExprSpec::Str("".into()),
                    ),
                    n2s(r("whole")),
                ),
                ExprSpec::Str(".".into()),
            ),
            call("lpad0", vec![n2s(r("frac")), num(4)]),
        ),
    };

    // take_at<T>(xs, k, i) = if i >= k or i == len(xs) then []
    //   else cons(xs[i], take_at(xs, k, i + 1))   — first k, clamped.
    let take_at = FunctionSpec {
        name: "take_at".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("xs", list(var("T"))),
            p("k", Type::Number),
            p("i", Type::Number),
        ],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            bop(BinOp::Or, bop(BinOp::Ge, r("i"), r("k")), eq(r("i"), r("n"))),
            empty(var("T")),
            cons(
                lget(r("xs"), r("i")),
                call("take_at", vec![r("xs"), r("k"), add1(r("i"))]),
            ),
        ),
    };
    let take = FunctionSpec {
        name: "take".into(),
        type_params: tp(&["T"]),
        params: vec![p("xs", list(var("T"))), p("k", Type::Number)],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("take_at", vec![r("xs"), r("k"), num(0)]),
    };
    // drop_at<T>(xs, k, i) = if i == len then []
    //   else if i < k then drop_at(xs,k,i+1)
    //   else cons(xs[i], drop_at(xs,k,i+1))       — all but first k.
    let drop_at = FunctionSpec {
        name: "drop_at".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("xs", list(var("T"))),
            p("k", Type::Number),
            p("i", Type::Number),
        ],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            eq(r("i"), r("n")),
            empty(var("T")),
            iff(
                bop(BinOp::Lt, r("i"), r("k")),
                call("drop_at", vec![r("xs"), r("k"), add1(r("i"))]),
                cons(
                    lget(r("xs"), r("i")),
                    call("drop_at", vec![r("xs"), r("k"), add1(r("i"))]),
                ),
            ),
        ),
    };
    let drop = FunctionSpec {
        name: "drop".into(),
        type_params: tp(&["T"]),
        params: vec![p("xs", list(var("T"))), p("k", Type::Number)],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("drop_at", vec![r("xs"), r("k"), num(0)]),
    };

    // rev_at<T>(xs, i) = if i < 0 then [] else cons(xs[i], rev_at(xs,i-1))
    let rev_at = FunctionSpec {
        name: "rev_at".into(),
        type_params: tp(&["T"]),
        params: vec![p("xs", list(var("T"))), p("i", Type::Number)],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: iff(
            bop(BinOp::Lt, r("i"), num(0)),
            empty(var("T")),
            cons(
                lget(r("xs"), r("i")),
                call(
                    "rev_at",
                    vec![r("xs"), bop(BinOp::Sub, r("i"), num(1))],
                ),
            ),
        ),
    };
    let reverse = FunctionSpec {
        name: "reverse".into(),
        type_params: tp(&["T"]),
        params: vec![p("xs", list(var("T")))],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call(
            "rev_at",
            vec![r("xs"), bop(BinOp::Sub, llen(r("xs")), num(1))],
        ),
    };
    // flat_map_at<T,U>(f, xs, i) = if i == len then []
    //   else concat(f(xs[i]), flat_map_at(f, xs, i + 1))
    let flat_map_at = FunctionSpec {
        name: "flat_map_at".into(),
        type_params: tp(&["T", "U"]),
        params: vec![
            p("f", fnt(vec![var("T")], list(var("U")))),
            p("xs", list(var("T"))),
            p("i", Type::Number),
        ],
        produces: ext(list(var("U"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            eq(r("i"), r("n")),
            empty(var("U")),
            call(
                "concat",
                vec![
                    callv(r("f"), vec![lget(r("xs"), r("i"))]),
                    call("flat_map_at", vec![r("f"), r("xs"), add1(r("i"))]),
                ],
            ),
        ),
    };
    let flat_map = FunctionSpec {
        name: "flat_map".into(),
        type_params: tp(&["T", "U"]),
        params: vec![
            p("f", fnt(vec![var("T")], list(var("U")))),
            p("xs", list(var("T"))),
        ],
        produces: ext(list(var("U"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("flat_map_at", vec![r("f"), r("xs"), num(0)]),
    };

    // ins<T>(le, x, ys) — insert x into the already-sorted ys before
    // the first element it is `le`-before-or-equal to. `le` is threaded
    // explicitly (never captured) so no closure holds a function value.
    let ins = FunctionSpec {
        name: "ins".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("le", fnt(vec![var("T"), var("T")], Type::Bool)),
            p("x", var("T")),
            p("ys", list(var("T"))),
        ],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("ys")))],
        result: iff(
            eq(r("n"), num(0)),
            cons(r("x"), empty(var("T"))),
            iff(
                callv(r("le"), vec![r("x"), lget(r("ys"), num(0))]),
                cons(r("x"), r("ys")),
                cons(
                    lget(r("ys"), num(0)),
                    call(
                        "ins",
                        vec![
                            r("le"),
                            r("x"),
                            call("drop", vec![r("ys"), num(1)]),
                        ],
                    ),
                ),
            ),
        ),
    };
    // sort_at<T>(le, xs, i, acc) = insertion sort (O(n^2) — fine for a
    // stdlib; documented). acc stays sorted; each xs[i] is `ins`-ed.
    let sort_at = FunctionSpec {
        name: "sort_at".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("le", fnt(vec![var("T"), var("T")], Type::Bool)),
            p("xs", list(var("T"))),
            p("i", Type::Number),
            p("acc", list(var("T"))),
        ],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            eq(r("i"), r("n")),
            r("acc"),
            call(
                "sort_at",
                vec![
                    r("le"),
                    r("xs"),
                    add1(r("i")),
                    call("ins", vec![r("le"), lget(r("xs"), r("i")), r("acc")]),
                ],
            ),
        ),
    };
    let sort_by = FunctionSpec {
        name: "sort_by".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("le", fnt(vec![var("T"), var("T")], Type::Bool)),
            p("xs", list(var("T"))),
        ],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call(
            "sort_at",
            vec![r("le"), r("xs"), num(0), empty(var("T"))],
        ),
    };

    // zip_at<A,B,C>(f, as, bs, i) = stop at the shorter length;
    //   else cons(f(as[i], bs[i]), zip_at(f, as, bs, i + 1))
    let zip_at = FunctionSpec {
        name: "zip_at".into(),
        type_params: tp(&["A", "B", "C"]),
        params: vec![
            p("f", fnt(vec![var("A"), var("B")], var("C"))),
            p("as", list(var("A"))),
            p("bs", list(var("B"))),
            p("i", Type::Number),
        ],
        produces: ext(list(var("C"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![
            step("na", llen(r("as"))),
            step("nb", llen(r("bs"))),
        ],
        result: iff(
            bop(
                BinOp::Or,
                bop(BinOp::Ge, r("i"), r("na")),
                bop(BinOp::Ge, r("i"), r("nb")),
            ),
            empty(var("C")),
            cons(
                callv(
                    r("f"),
                    vec![lget(r("as"), r("i")), lget(r("bs"), r("i"))],
                ),
                call("zip_at", vec![r("f"), r("as"), r("bs"), add1(r("i"))]),
            ),
        ),
    };
    let zip_with = FunctionSpec {
        name: "zip_with".into(),
        type_params: tp(&["A", "B", "C"]),
        params: vec![
            p("f", fnt(vec![var("A"), var("B")], var("C"))),
            p("as", list(var("A"))),
            p("bs", list(var("B"))),
        ],
        produces: ext(list(var("C"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("zip_at", vec![r("f"), r("as"), r("bs"), num(0)]),
    };
    // dd_at<T>(eq, xs, i) — adjacent dedup (Unix `uniq`): drop xs[i]
    //   when it `eq`s xs[i-1]. `eq` threaded explicitly (no capture).
    let dd_at = FunctionSpec {
        name: "dd_at".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("eq", fnt(vec![var("T"), var("T")], Type::Bool)),
            p("xs", list(var("T"))),
            p("i", Type::Number),
        ],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            eq(r("i"), r("n")),
            empty(var("T")),
            iff(
                bop(BinOp::Eq, r("i"), num(0)),
                cons(
                    lget(r("xs"), num(0)),
                    call("dd_at", vec![r("eq"), r("xs"), num(1)]),
                ),
                iff(
                    callv(
                        r("eq"),
                        vec![
                            lget(r("xs"), r("i")),
                            lget(r("xs"), bop(BinOp::Sub, r("i"), num(1))),
                        ],
                    ),
                    call("dd_at", vec![r("eq"), r("xs"), add1(r("i"))]),
                    cons(
                        lget(r("xs"), r("i")),
                        call("dd_at", vec![r("eq"), r("xs"), add1(r("i"))]),
                    ),
                ),
            ),
        ),
    };
    let dedup_by = FunctionSpec {
        name: "dedup_by".into(),
        type_params: tp(&["T"]),
        params: vec![
            p("eq", fnt(vec![var("T"), var("T")], Type::Bool)),
            p("xs", list(var("T"))),
        ],
        produces: ext(list(var("T"))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("dd_at", vec![r("eq"), r("xs"), num(0)]),
    };

    // join_at(sep, xs, i) = ""           if i == len
    //   xs[0] ++ rest                    if i == 0
    //   sep ++ xs[i] ++ rest             otherwise
    let join_at = FunctionSpec {
        name: "join_at".into(),
        type_params: vec![],
        params: vec![
            p("sep", Type::String),
            p("xs", list(Type::String)),
            p("i", Type::Number),
        ],
        produces: ext(Type::String),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            eq(r("i"), r("n")),
            ExprSpec::Str(String::new()),
            iff(
                eq(r("i"), num(0)),
                scat(
                    lget(r("xs"), num(0)),
                    call("join_at", vec![r("sep"), r("xs"), num(1)]),
                ),
                scat(
                    scat(r("sep"), lget(r("xs"), r("i"))),
                    call("join_at", vec![r("sep"), r("xs"), add1(r("i"))]),
                ),
            ),
        ),
    };
    let str_join = FunctionSpec {
        name: "str_join".into(),
        type_params: vec![],
        params: vec![p("sep", Type::String), p("xs", list(Type::String))],
        produces: ext(Type::String),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("join_at", vec![r("sep"), r("xs"), num(0)]),
    };
    // rep_at(s, n, i) = if i >= n then "" else s ++ rep_at(s, n, i+1)
    let rep_at = FunctionSpec {
        name: "rep_at".into(),
        type_params: vec![],
        params: vec![
            p("s", Type::String),
            p("n", Type::Number),
            p("i", Type::Number),
        ],
        produces: ext(Type::String),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: iff(
            bop(BinOp::Ge, r("i"), r("n")),
            ExprSpec::Str(String::new()),
            scat(
                r("s"),
                call("rep_at", vec![r("s"), r("n"), add1(r("i"))]),
            ),
        ),
    };
    let str_repeat = FunctionSpec {
        name: "str_repeat".into(),
        type_params: vec![],
        params: vec![p("s", Type::String), p("n", Type::Number)],
        produces: ext(Type::String),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("rep_at", vec![r("s"), r("n"), num(0)]),
    };

    let sl = |s: ExprSpec, a: ExprSpec, b: ExprSpec| ExprSpec::StrSlice {
        s: Box::new(s),
        start: Box::new(a),
        len: Box::new(b),
    };
    let slen_ = |x: ExprSpec| ExprSpec::StrLen(Box::new(x));
    let sidx = |h: ExprSpec, n: ExprSpec| ExprSpec::StrIndexOf {
        haystack: Box::new(h),
        needle: Box::new(n),
    };
    let seq = |a: ExprSpec, b: ExprSpec| ExprSpec::StrEq(Box::new(a), Box::new(b));
    let sub1 = |x: ExprSpec| bop(BinOp::Sub, x, num(1));
    // is_ws(c) — c is one byte; ASCII space / tab / NL / CR.
    let is_ws = FunctionSpec {
        name: "is_ws".into(),
        type_params: vec![],
        params: vec![p("c", Type::String)],
        produces: ext(Type::Bool),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: bop(
            BinOp::Or,
            bop(
                BinOp::Or,
                seq(r("c"), ExprSpec::Str(" ".into())),
                seq(r("c"), ExprSpec::Str("\t".into())),
            ),
            bop(
                BinOp::Or,
                seq(r("c"), ExprSpec::Str("\n".into())),
                seq(r("c"), ExprSpec::Str("\r".into())),
            ),
        ),
    };
    // lead(s, i) — first non-ws index (== len if all ws / empty).
    let lead = FunctionSpec {
        name: "lead".into(),
        type_params: vec![],
        params: vec![p("s", Type::String), p("i", Type::Number)],
        produces: ext(Type::Number),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", slen_(r("s")))],
        result: iff(
            bop(BinOp::Ge, r("i"), r("n")),
            r("n"),
            iff(
                call("is_ws", vec![sl(r("s"), r("i"), num(1))]),
                call("lead", vec![r("s"), add1(r("i"))]),
                r("i"),
            ),
        ),
    };
    // tend(s, i) — one past the last non-ws index (0 if all ws).
    let tend = FunctionSpec {
        name: "tend".into(),
        type_params: vec![],
        params: vec![p("s", Type::String), p("i", Type::Number)],
        produces: ext(Type::Number),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: iff(
            bop(BinOp::Lt, r("i"), num(0)),
            num(0),
            iff(
                call("is_ws", vec![sl(r("s"), r("i"), num(1))]),
                call("tend", vec![r("s"), sub1(r("i"))]),
                add1(r("i")),
            ),
        ),
    };
    let str_trim = FunctionSpec {
        name: "str_trim".into(),
        type_params: vec![],
        params: vec![p("s", Type::String)],
        produces: ext(Type::String),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![
            step("st", call("lead", vec![r("s"), num(0)])),
            step("en", call("tend", vec![r("s"), sub1(slen_(r("s")))])),
        ],
        result: iff(
            bop(BinOp::Ge, r("st"), r("en")),
            ExprSpec::Str(String::new()),
            sl(r("s"), r("st"), bop(BinOp::Sub, r("en"), r("st"))),
        ),
    };
    // rep(s, from, to) — replace every non-overlapping `from`. Empty
    // `from` returns `s` unchanged (no infinite loop).
    let rep = FunctionSpec {
        name: "rep".into(),
        type_params: vec![],
        params: vec![
            p("s", Type::String),
            p("from", Type::String),
            p("to", Type::String),
        ],
        produces: ext(Type::String),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![
            step("fl", slen_(r("from"))),
            step("ix", sidx(r("s"), r("from"))),
        ],
        result: iff(
            bop(BinOp::Eq, r("fl"), num(0)),
            r("s"),
            iff(
                bop(BinOp::Lt, r("ix"), num(0)),
                r("s"),
                scat(
                    scat(sl(r("s"), num(0), r("ix")), r("to")),
                    call(
                        "rep",
                        vec![
                            sl(
                                r("s"),
                                bop(BinOp::Add, r("ix"), r("fl")),
                                bop(
                                    BinOp::Sub,
                                    slen_(r("s")),
                                    bop(BinOp::Add, r("ix"), r("fl")),
                                ),
                            ),
                            r("from"),
                            r("to"),
                        ],
                    ),
                ),
            ),
        ),
    };
    let str_replace = FunctionSpec {
        name: "str_replace".into(),
        type_params: vec![],
        params: vec![
            p("s", Type::String),
            p("from", Type::String),
            p("to", Type::String),
        ],
        produces: ext(Type::String),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: call("rep", vec![r("s"), r("from"), r("to")]),
    };

    // Option ergonomics. Cairn variants/records are nominal &
    // monomorphic, so there is no generic `Result<T,E>` at stdlib
    // level (a decided boundary — design.md §9): the fallible-value
    // story is built-in `Option<T>` plus the language `Fail`/`Handle`.
    // first/last give the safe ends of a list.
    let first = FunctionSpec {
        name: "first".into(),
        type_params: tp(&["T"]),
        params: vec![p("xs", list(var("T")))],
        produces: ext(Type::Option(Box::new(var("T")))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            eq(r("n"), num(0)),
            none(var("T")),
            some(lget(r("xs"), num(0))),
        ),
    };
    let last = FunctionSpec {
        name: "last".into(),
        type_params: tp(&["T"]),
        params: vec![p("xs", list(var("T")))],
        produces: ext(Type::Option(Box::new(var("T")))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![step("n", llen(r("xs")))],
        result: iff(
            eq(r("n"), num(0)),
            none(var("T")),
            some(lget(r("xs"), bop(BinOp::Sub, r("n"), num(1)))),
        ),
    };

    // opt_map(f, o)  : Some(f(v)) | None
    // opt_then(f, o) : f(v)       | None   (monadic bind)
    let omatch = |o: ExprSpec, sb: ExprSpec, nb: ExprSpec| {
        ExprSpec::OptionMatch {
            opt: Box::new(o),
            some_bind: "v".into(),
            some_body: Box::new(sb),
            none_body: Box::new(nb),
        }
    };
    let opt_map = FunctionSpec {
        name: "opt_map".into(),
        type_params: tp(&["T", "U"]),
        params: vec![
            p("f", fnt(vec![var("T")], var("U"))),
            p("o", Type::Option(Box::new(var("T")))),
        ],
        produces: ext(Type::Option(Box::new(var("U")))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: omatch(
            r("o"),
            some(callv(r("f"), vec![r("v")])),
            none(var("U")),
        ),
    };
    let opt_then = FunctionSpec {
        name: "opt_then".into(),
        type_params: tp(&["T", "U"]),
        params: vec![
            p("f", fnt(vec![var("T")], Type::Option(Box::new(var("U"))))),
            p("o", Type::Option(Box::new(var("T")))),
        ],
        produces: ext(Type::Option(Box::new(var("U")))),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result: omatch(
            r("o"),
            callv(r("f"), vec![r("v")]),
            none(var("U")),
        ),
    };

    // Integer helpers (pure Number; no language-core change — Float
    // transcendental math would be a Node+wasm-intrinsic pipeline-add,
    // out of scope here by design).
    let nf0 = |name: &str, params: Vec<Param>, result: ExprSpec| FunctionSpec {
        name: name.into(),
        type_params: vec![],
        params,
        produces: ext(Type::Number),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![],
        result,
    };
    let iabs = nf0(
        "iabs",
        vec![p("x", Type::Number)],
        iff(
            bop(BinOp::Lt, r("x"), num(0)),
            bop(BinOp::Sub, num(0), r("x")),
            r("x"),
        ),
    );
    let imin = nf0(
        "imin",
        vec![p("a", Type::Number), p("b", Type::Number)],
        iff(bop(BinOp::Lt, r("a"), r("b")), r("a"), r("b")),
    );
    let imax = nf0(
        "imax",
        vec![p("a", Type::Number), p("b", Type::Number)],
        iff(bop(BinOp::Gt, r("a"), r("b")), r("a"), r("b")),
    );
    let clamp = nf0(
        "clamp",
        vec![
            p("x", Type::Number),
            p("lo", Type::Number),
            p("hi", Type::Number),
        ],
        call(
            "imax",
            vec![r("lo"), call("imin", vec![r("x"), r("hi")])],
        ),
    );

    // ipow(base, exp) — exp <= 0 yields 1 (documented). gcd via Euclid
    // on the signed remainder; the iabs at b==0 normalises the sign.
    let ipow = nf0(
        "ipow",
        vec![p("base", Type::Number), p("exp", Type::Number)],
        iff(
            bop(BinOp::Le, r("exp"), num(0)),
            num(1),
            bop(
                BinOp::Mul,
                r("base"),
                call(
                    "ipow",
                    vec![r("base"), bop(BinOp::Sub, r("exp"), num(1))],
                ),
            ),
        ),
    );
    let gcd = nf0(
        "gcd",
        vec![p("a", Type::Number), p("b", Type::Number)],
        iff(
            bop(BinOp::Eq, r("b"), num(0)),
            call("iabs", vec![r("a")]),
            call(
                "gcd",
                vec![r("b"), bop(BinOp::Mod, r("a"), r("b"))],
            ),
        ),
    );

    // decimal_round_str(d, places) — round a Decimal half-up (away
    // from zero) to `places` (clamped 0..4) fractional digits and
    // format it. Returns a String, not a Decimal: reconstructing a
    // Decimal from a rounded raw would need a raw->Decimal core
    // primitive (Decimal is a scaled i64; `DecimalRaw` is the one-way
    // identity) — a language-core pipeline-add, out of scope for the
    // stdlib track by design. Display is the real need; this covers it,
    // composed from clamp/ipow/iabs/lpad0 (the stdlib using itself).
    let dr = FunctionSpec {
        name: "decimal_round_str".into(),
        type_params: vec![],
        params: vec![p("d", Type::Decimal), p("places", Type::Number)],
        produces: ext(Type::String),
        requires: BTreeSet::new(),
        on_failure: vec![],
        steps: vec![
            step("raw", ExprSpec::DecimalRaw(Box::new(r("d")))),
            step("m", call("iabs", vec![r("raw")])),
            step("pl", call("clamp", vec![r("places"), num(0), num(4)])),
            step(
                "f",
                call(
                    "ipow",
                    vec![num(10), bop(BinOp::Sub, num(4), r("pl"))],
                ),
            ),
            // round half-up: ((m + f/2) / f) * f, still scaled by 10000.
            step(
                "rnd",
                bop(
                    BinOp::Mul,
                    bop(
                        BinOp::Div,
                        bop(
                            BinOp::Add,
                            r("m"),
                            bop(BinOp::Div, r("f"), num(2)),
                        ),
                        r("f"),
                    ),
                    r("f"),
                ),
            ),
            step("whole", bop(BinOp::Div, r("rnd"), num(10_000))),
            step(
                "frac",
                bop(
                    BinOp::Div,
                    bop(BinOp::Mod, r("rnd"), num(10_000)),
                    r("f"),
                ),
            ),
            step(
                "sign",
                iff(
                    bop(BinOp::Lt, r("raw"), num(0)),
                    ExprSpec::Str("-".into()),
                    ExprSpec::Str(String::new()),
                ),
            ),
        ],
        result: scat(
            scat(r("sign"), n2s(r("whole"))),
            iff(
                bop(BinOp::Eq, r("pl"), num(0)),
                ExprSpec::Str(String::new()),
                scat(
                    ExprSpec::Str(".".into()),
                    call("lpad0", vec![n2s(r("frac")), r("pl")]),
                ),
            ),
        ),
    };

    vec![
        fold_at, fold, map_at, map, filter_at, filter, range_at, range,
        any_at, any, all_at, all, find_at, find, concat_at, concat,
        lpad0, decimal_to_str, take_at, take, drop_at, drop, rev_at,
        reverse, flat_map_at, flat_map, ins, sort_at, sort_by, zip_at,
        zip_with, dd_at, dedup_by, join_at, str_join, rep_at, str_repeat,
        is_ws, lead, tend, str_trim, rep, str_replace, first, last,
        opt_map, opt_then, iabs, imin, imax, clamp, ipow, gcd, dr,
    ]
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::edit::{Editor, ModuleSpec};
    use crate::store::Store;
    use crate::wasm::{lower, run_i64};

    /// Audit B8: `decimal_to_str` renders exact fixed-point money
    /// (sign + whole + 4 frac digits), authored in Cairn over the
    /// full-range `num_to_str`. Probes compare via StrEq → Bool.
    #[test]
    fn decimal_to_str_formats() {
        let probe = |name: &str, v: f64, want: &str| FunctionSpec {
            name: name.into(),
            type_params: vec![],
            params: vec![],
            produces: ext(Type::Bool),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result: ExprSpec::StrEq(
                Box::new(call(
                    "decimal_to_str",
                    vec![ExprSpec::Decimal(v)],
                )),
                Box::new(ExprSpec::Str(want.into())),
            ),
        };
        let cases = [
            ("a", 1.25, "1.2500"),
            ("b", 19.99, "19.9900"),
            ("c", -0.5, "-0.5000"),
            ("d", 0.0, "0.0000"),
            ("e", 1000.0, "1000.0000"),
            ("f", -12.3456, "-12.3456"),
        ];
        let mut fns = list_functions();
        fns.extend(cases.iter().map(|(n, v, w)| probe(n, *v, w)));
        let e = Editor::new(Store::open_in_memory().unwrap());
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "dec".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);
        let wasm = lower(e.store(), &m).unwrap();
        for (n, _, w) in cases {
            assert_eq!(
                run_i64(&wasm, n, &[]).unwrap(),
                1,
                "decimal_to_str should produce {w}"
            );
        }
    }

    /// Author the stdlib + a caller that uses `map`/`filter`/`fold`
    /// through closures, then check, lower, and run it end to end.
    #[test]
    fn the_stdlib_maps_filters_and_folds() {
        // sum_doubled_evens(xs) =
        //   fold(|a,x| a + x, 0, map(|x| x*2, filter(|x| x % 2 == 0, xs)))
        let lam = |params: Vec<(&str, Type)>, body: ExprSpec| ExprSpec::Lambda {
            params: params
                .into_iter()
                .map(|(n, t)| (n.to_string(), t))
                .collect(),
            body: Box::new(body),
        };
        let bin = |op, a: ExprSpec, b: ExprSpec| ExprSpec::BinOp {
            op,
            lhs: Box::new(a),
            rhs: Box::new(b),
        };

        let is_even = lam(
            vec![("x", Type::Number)],
            bin(BinOp::Eq, bin(BinOp::Mod, r("x"), num(2)), num(0)),
        );
        let double = lam(vec![("x", Type::Number)], bin(BinOp::Mul, r("x"), num(2)));
        let plus = lam(
            vec![("a", Type::Number), ("x", Type::Number)],
            bin(BinOp::Add, r("a"), r("x")),
        );

        // run() = fold(|a,x| a+x, 0, map(|x| x*2, filter(even, [1..6])))
        //   evens [2,4,6] -> doubled [4,8,12] -> sum 24.
        let xs = ExprSpec::List((1..=6).map(num).collect());
        let caller = FunctionSpec {
            name: "run".into(),
            type_params: vec![],
            params: vec![],
            produces: ext(Type::Number),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result: call(
                "fold",
                vec![
                    plus,
                    num(0),
                    call("map", vec![double, call("filter", vec![is_even, xs])]),
                ],
            ),
        };

        let e = Editor::new(Store::open_in_memory().unwrap());
        let mut fns = list_functions();
        fns.push(caller);
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "stdtest".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);

        let wasm = lower(e.store(), &m).unwrap();
        assert_eq!(run_i64(&wasm, "run", &[]).unwrap(), 24);
    }

    /// range / any / all / find — find returns Option<T>, consumed with
    /// OptionMatch (the whole keystone chain in one path).
    #[test]
    fn the_stdlib_ranges_searches_and_quantifies() {
        let lam = |params: Vec<(&str, Type)>, body: ExprSpec| ExprSpec::Lambda {
            params: params
                .into_iter()
                .map(|(n, t)| (n.to_string(), t))
                .collect(),
            body: Box::new(body),
        };
        let bin = |op, a: ExprSpec, b: ExprSpec| ExprSpec::BinOp {
            op,
            lhs: Box::new(a),
            rhs: Box::new(b),
        };
        let nums = |vs: &[i64]| ExprSpec::List(vs.iter().copied().map(num).collect());
        let nfn = |name: &str, ret: Type, result: ExprSpec| FunctionSpec {
            name: name.into(),
            type_params: vec![],
            params: vec![],
            produces: ext(ret),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result,
        };
        let nullary = |name: &str, result: ExprSpec| nfn(name, Type::Number, result);
        let plus = || {
            lam(
                vec![("a", Type::Number), ("x", Type::Number)],
                bin(BinOp::Add, r("a"), r("x")),
            )
        };
        let find_or = |pred: ExprSpec, xs: ExprSpec| ExprSpec::OptionMatch {
            opt: Box::new(call("find", vec![pred, xs])),
            some_bind: "v".into(),
            some_body: Box::new(r("v")),
            none_body: Box::new(num(-1)),
        };

        let mut fns = list_functions();
        fns.extend([
            // sum of range(1,5) = 1+2+3+4 = 10
            nullary(
                "r_sum",
                call("fold", vec![plus(), num(0), call("range", vec![num(1), num(5)])]),
            ),
            // any x == 3 in [1,2,3] -> true(1)
            nfn(
                "anyt",
                Type::Bool,
                call(
                    "any",
                    vec![
                        lam(vec![("x", Type::Number)], bin(BinOp::Eq, r("x"), num(3))),
                        nums(&[1, 2, 3]),
                    ],
                ),
            ),
            // all x > 0 -> true ; all x > 1 -> false
            nfn(
                "allt",
                Type::Bool,
                call(
                    "all",
                    vec![
                        lam(vec![("x", Type::Number)], bin(BinOp::Gt, r("x"), num(0))),
                        nums(&[1, 2, 3]),
                    ],
                ),
            ),
            nfn(
                "allf",
                Type::Bool,
                call(
                    "all",
                    vec![
                        lam(vec![("x", Type::Number)], bin(BinOp::Gt, r("x"), num(1))),
                        nums(&[1, 2, 3]),
                    ],
                ),
            ),
            // find x > 2 in [1,2,3,4] -> Some(3) ; find x > 9 -> None
            nullary(
                "find_hit",
                find_or(
                    lam(vec![("x", Type::Number)], bin(BinOp::Gt, r("x"), num(2))),
                    nums(&[1, 2, 3, 4]),
                ),
            ),
            nullary(
                "find_miss",
                find_or(
                    lam(vec![("x", Type::Number)], bin(BinOp::Gt, r("x"), num(9))),
                    nums(&[1, 2, 3, 4]),
                ),
            ),
        ]);

        let e = Editor::new(Store::open_in_memory().unwrap());
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "stdtest2".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);
        let wasm = lower(e.store(), &m).unwrap();
        assert_eq!(run_i64(&wasm, "r_sum", &[]).unwrap(), 10);
        assert_eq!(run_i64(&wasm, "anyt", &[]).unwrap(), 1);
        assert_eq!(run_i64(&wasm, "allt", &[]).unwrap(), 1);
        assert_eq!(run_i64(&wasm, "allf", &[]).unwrap(), 0);
        assert_eq!(run_i64(&wasm, "find_hit", &[]).unwrap(), 3);
        assert_eq!(run_i64(&wasm, "find_miss", &[]).unwrap(), -1);
    }

    /// take / drop: first-k and all-but-first-k, both clamped (k=0,
    /// k>len never trap — the guards check `len` before any index).
    #[test]
    fn the_stdlib_takes_and_drops() {
        let lam = |params: Vec<(&str, Type)>, body: ExprSpec| ExprSpec::Lambda {
            params: params
                .into_iter()
                .map(|(n, t)| (n.to_string(), t))
                .collect(),
            body: Box::new(body),
        };
        let bin = |op, a: ExprSpec, b: ExprSpec| ExprSpec::BinOp {
            op,
            lhs: Box::new(a),
            rhs: Box::new(b),
        };
        let xs = || ExprSpec::List([10, 20, 30, 40, 50].iter().copied().map(num).collect());
        let plus = || {
            lam(
                vec![("a", Type::Number), ("x", Type::Number)],
                bin(BinOp::Add, r("a"), r("x")),
            )
        };
        let sum = |l: ExprSpec| call("fold", vec![plus(), num(0), l]);
        let nf = |name: &str, result: ExprSpec| FunctionSpec {
            name: name.into(),
            type_params: vec![],
            params: vec![],
            produces: ext(Type::Number),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result,
        };
        let mut fns = list_functions();
        fns.extend([
            nf("t_take2", sum(call("take", vec![xs(), num(2)]))), // 10+20
            nf("t_drop2", sum(call("drop", vec![xs(), num(2)]))), // 30+40+50
            nf("t_take_over", llen(call("take", vec![xs(), num(99)]))), // 5
            nf("t_take_zero", llen(call("take", vec![xs(), num(0)]))), // 0
            nf("t_drop_zero", llen(call("drop", vec![xs(), num(0)]))), // 5
            nf("t_drop_over", llen(call("drop", vec![xs(), num(99)]))), // 0
        ]);
        let e = Editor::new(Store::open_in_memory().unwrap());
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "stdtake".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);
        let wasm = lower(e.store(), &m).unwrap();
        assert_eq!(run_i64(&wasm, "t_take2", &[]).unwrap(), 30);
        assert_eq!(run_i64(&wasm, "t_drop2", &[]).unwrap(), 120);
        assert_eq!(run_i64(&wasm, "t_take_over", &[]).unwrap(), 5);
        assert_eq!(run_i64(&wasm, "t_take_zero", &[]).unwrap(), 0);
        assert_eq!(run_i64(&wasm, "t_drop_zero", &[]).unwrap(), 5);
        assert_eq!(run_i64(&wasm, "t_drop_over", &[]).unwrap(), 0);
    }

    /// reverse (empty-safe via the i<0 guard) and flat_map (concat of a
    /// list-returning closure over the input).
    #[test]
    fn the_stdlib_reverses_and_flat_maps() {
        let lam = |params: Vec<(&str, Type)>, body: ExprSpec| ExprSpec::Lambda {
            params: params
                .into_iter()
                .map(|(n, t)| (n.to_string(), t))
                .collect(),
            body: Box::new(body),
        };
        let bin = |op, a: ExprSpec, b: ExprSpec| ExprSpec::BinOp {
            op,
            lhs: Box::new(a),
            rhs: Box::new(b),
        };
        let nums = |vs: &[i64]| ExprSpec::List(vs.iter().copied().map(num).collect());
        let nf = |name: &str, result: ExprSpec| FunctionSpec {
            name: name.into(),
            type_params: vec![],
            params: vec![],
            produces: ext(Type::Number),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result,
        };
        // fold(|a,x| a*10+x, 0, ·) reads a digit list as a number, so
        // reverse([1,2,3]) -> 321 is an exact, order-sensitive probe.
        let horner = || {
            lam(
                vec![("a", Type::Number), ("x", Type::Number)],
                bin(BinOp::Add, bin(BinOp::Mul, r("a"), num(10)), r("x")),
            )
        };
        let dig = |l: ExprSpec| call("fold", vec![horner(), num(0), l]);
        let dup = || {
            lam(
                vec![("x", Type::Number)],
                ExprSpec::List(vec![r("x"), r("x")]),
            )
        };
        let mut fns = list_functions();
        fns.extend([
            nf("rev3", dig(call("reverse", vec![nums(&[1, 2, 3])]))), // 321
            nf(
                "rev_empty",
                llen(call("reverse", vec![empty(Type::Number)])),
            ), // 0
            nf(
                "fm_dup",
                dig(call("flat_map", vec![dup(), nums(&[1, 2, 3])])),
            ), // [1,1,2,2,3,3] -> 112233
            nf(
                "fm_len",
                llen(call("flat_map", vec![dup(), nums(&[4, 5])])),
            ), // 4
        ]);
        let e = Editor::new(Store::open_in_memory().unwrap());
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "stdrev".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);
        let wasm = lower(e.store(), &m).unwrap();
        assert_eq!(run_i64(&wasm, "rev3", &[]).unwrap(), 321);
        assert_eq!(run_i64(&wasm, "rev_empty", &[]).unwrap(), 0);
        assert_eq!(run_i64(&wasm, "fm_dup", &[]).unwrap(), 112233);
        assert_eq!(run_i64(&wasm, "fm_len", &[]).unwrap(), 4);
    }

    /// sort_by with a comparator closure: ascending (`<=`), descending
    /// (`>=`), already-sorted, and empty. `le` is threaded explicitly,
    /// so no closure ever captures a function value (§9 boundary).
    #[test]
    fn the_stdlib_sorts_by_a_comparator() {
        let lam = |params: Vec<(&str, Type)>, body: ExprSpec| ExprSpec::Lambda {
            params: params
                .into_iter()
                .map(|(n, t)| (n.to_string(), t))
                .collect(),
            body: Box::new(body),
        };
        let bin = |op, a: ExprSpec, b: ExprSpec| ExprSpec::BinOp {
            op,
            lhs: Box::new(a),
            rhs: Box::new(b),
        };
        let nums = |vs: &[i64]| ExprSpec::List(vs.iter().copied().map(num).collect());
        let nf = |name: &str, result: ExprSpec| FunctionSpec {
            name: name.into(),
            type_params: vec![],
            params: vec![],
            produces: ext(Type::Number),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result,
        };
        let le = || {
            lam(
                vec![("a", Type::Number), ("b", Type::Number)],
                bin(BinOp::Le, r("a"), r("b")),
            )
        };
        let ge = || {
            lam(
                vec![("a", Type::Number), ("b", Type::Number)],
                bin(BinOp::Ge, r("a"), r("b")),
            )
        };
        let horner = || {
            lam(
                vec![("a", Type::Number), ("x", Type::Number)],
                bin(BinOp::Add, bin(BinOp::Mul, r("a"), num(10)), r("x")),
            )
        };
        let dig = |l: ExprSpec| call("fold", vec![horner(), num(0), l]);
        let mut fns = list_functions();
        fns.extend([
            nf("asc", dig(call("sort_by", vec![le(), nums(&[3, 1, 2])]))), // 123
            nf("desc", dig(call("sort_by", vec![ge(), nums(&[3, 1, 2])]))), // 321
            nf(
                "already",
                dig(call("sort_by", vec![le(), nums(&[1, 2, 3])])),
            ), // 123
            nf(
                "sort_empty",
                llen(call("sort_by", vec![le(), empty(Type::Number)])),
            ), // 0
            nf(
                "asc5",
                dig(call("sort_by", vec![le(), nums(&[5, 4, 3, 2, 1])])),
            ), // 12345
        ]);
        let e = Editor::new(Store::open_in_memory().unwrap());
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "stdsort".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);
        let wasm = lower(e.store(), &m).unwrap();
        assert_eq!(run_i64(&wasm, "asc", &[]).unwrap(), 123);
        assert_eq!(run_i64(&wasm, "desc", &[]).unwrap(), 321);
        assert_eq!(run_i64(&wasm, "already", &[]).unwrap(), 123);
        assert_eq!(run_i64(&wasm, "sort_empty", &[]).unwrap(), 0);
        assert_eq!(run_i64(&wasm, "asc5", &[]).unwrap(), 12345);
    }

    /// zip_with (stops at the shorter input) and dedup_by (adjacent
    /// `uniq`), both threading the closure explicitly.
    #[test]
    fn the_stdlib_zips_and_dedups() {
        let lam = |params: Vec<(&str, Type)>, body: ExprSpec| ExprSpec::Lambda {
            params: params
                .into_iter()
                .map(|(n, t)| (n.to_string(), t))
                .collect(),
            body: Box::new(body),
        };
        let bin = |op, a: ExprSpec, b: ExprSpec| ExprSpec::BinOp {
            op,
            lhs: Box::new(a),
            rhs: Box::new(b),
        };
        let nums = |vs: &[i64]| ExprSpec::List(vs.iter().copied().map(num).collect());
        let nf = |name: &str, result: ExprSpec| FunctionSpec {
            name: name.into(),
            type_params: vec![],
            params: vec![],
            produces: ext(Type::Number),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result,
        };
        let plus = || {
            lam(
                vec![("a", Type::Number), ("x", Type::Number)],
                bin(BinOp::Add, r("a"), r("x")),
            )
        };
        let sum = |l: ExprSpec| call("fold", vec![plus(), num(0), l]);
        let addf = || {
            lam(
                vec![("a", Type::Number), ("b", Type::Number)],
                bin(BinOp::Add, r("a"), r("b")),
            )
        };
        let eqf = || {
            lam(
                vec![("a", Type::Number), ("b", Type::Number)],
                bin(BinOp::Eq, r("a"), r("b")),
            )
        };
        let horner = || {
            lam(
                vec![("a", Type::Number), ("x", Type::Number)],
                bin(BinOp::Add, bin(BinOp::Mul, r("a"), num(10)), r("x")),
            )
        };
        let dig = |l: ExprSpec| call("fold", vec![horner(), num(0), l]);
        let mut fns = list_functions();
        fns.extend([
            // [1,2,3]+[10,20,30] -> [11,22,33], sum 66
            nf(
                "zip_sum",
                sum(call(
                    "zip_with",
                    vec![addf(), nums(&[1, 2, 3]), nums(&[10, 20, 30])],
                )),
            ),
            // uneven: [1,2]+[10,20,30] -> [11,22], len 2
            nf(
                "zip_uneven_len",
                llen(call(
                    "zip_with",
                    vec![addf(), nums(&[1, 2]), nums(&[10, 20, 30])],
                )),
            ),
            // adjacent dedup: [1,1,2,2,2,3,1] -> [1,2,3,1] -> 1231
            nf(
                "dd",
                dig(call(
                    "dedup_by",
                    vec![eqf(), nums(&[1, 1, 2, 2, 2, 3, 1])],
                )),
            ),
            nf(
                "dd_empty",
                llen(call("dedup_by", vec![eqf(), empty(Type::Number)])),
            ),
        ]);
        let e = Editor::new(Store::open_in_memory().unwrap());
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "stdzip".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);
        let wasm = lower(e.store(), &m).unwrap();
        assert_eq!(run_i64(&wasm, "zip_sum", &[]).unwrap(), 66);
        assert_eq!(run_i64(&wasm, "zip_uneven_len", &[]).unwrap(), 2);
        assert_eq!(run_i64(&wasm, "dd", &[]).unwrap(), 1231);
        assert_eq!(run_i64(&wasm, "dd_empty", &[]).unwrap(), 0);
    }

    /// str_join (separator only between elements; empty/single safe) and
    /// str_repeat (n<=0 → ""). Probes compare via StrEq → Bool.
    #[test]
    fn the_stdlib_joins_and_repeats() {
        let strs = |vs: &[&str]| {
            ExprSpec::List(vs.iter().map(|s| ExprSpec::Str((*s).into())).collect())
        };
        let probe = |name: &str, got: ExprSpec, want: &str| FunctionSpec {
            name: name.into(),
            type_params: vec![],
            params: vec![],
            produces: ext(Type::Bool),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result: ExprSpec::StrEq(
                Box::new(got),
                Box::new(ExprSpec::Str(want.into())),
            ),
        };
        let mut fns = list_functions();
        fns.extend([
            probe(
                "j_abc",
                call(
                    "str_join",
                    vec![ExprSpec::Str(", ".into()), strs(&["a", "b", "c"])],
                ),
                "a, b, c",
            ),
            probe(
                "j_empty",
                call(
                    "str_join",
                    vec![
                        ExprSpec::Str("-".into()),
                        ExprSpec::ListEmpty { elem: Type::String },
                    ],
                ),
                "",
            ),
            probe(
                "j_one",
                call(
                    "str_join",
                    vec![ExprSpec::Str("-".into()), strs(&["x"])],
                ),
                "x",
            ),
            probe(
                "r_ab3",
                call(
                    "str_repeat",
                    vec![ExprSpec::Str("ab".into()), num(3)],
                ),
                "ababab",
            ),
            probe(
                "r_zero",
                call(
                    "str_repeat",
                    vec![ExprSpec::Str("z".into()), num(0)],
                ),
                "",
            ),
        ]);
        let e = Editor::new(Store::open_in_memory().unwrap());
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "stdjoin".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);
        let wasm = lower(e.store(), &m).unwrap();
        for n in ["j_abc", "j_empty", "j_one", "r_ab3", "r_zero"] {
            assert_eq!(run_i64(&wasm, n, &[]).unwrap(), 1, "{n}");
        }
    }

    /// str_trim (leading/trailing ASCII ws, all-ws → "", empty-safe) and
    /// str_replace (all non-overlapping; empty `from` is a no-op).
    #[test]
    fn the_stdlib_trims_and_replaces() {
        let probe = |name: &str, got: ExprSpec, want: &str| FunctionSpec {
            name: name.into(),
            type_params: vec![],
            params: vec![],
            produces: ext(Type::Bool),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result: ExprSpec::StrEq(
                Box::new(got),
                Box::new(ExprSpec::Str(want.into())),
            ),
        };
        let s = |x: &str| ExprSpec::Str(x.into());
        let tr = |x: &str| call("str_trim", vec![s(x)]);
        let rp = |a: &str, b: &str, c: &str| {
            call("str_replace", vec![s(a), s(b), s(c)])
        };
        let mut fns = list_functions();
        fns.extend([
            probe("t_pad", tr("  hi  "), "hi"),
            probe("t_id", tr("x"), "x"),
            probe("t_allws", tr("   "), ""),
            probe("t_mixed", tr("\t a \n"), "a"),
            probe("t_empty", tr(""), ""),
            probe("rp_dots", rp("a.b.c", ".", "-"), "a-b-c"),
            probe("rp_grow", rp("aaa", "a", "bb"), "bbbbbb"),
            probe("rp_none", rp("none", "x", "y"), "none"),
            probe("rp_empty_from", rp("abc", "", "-"), "abc"),
        ]);
        let e = Editor::new(Store::open_in_memory().unwrap());
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "stdtrim".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);
        let wasm = lower(e.store(), &m).unwrap();
        for n in [
            "t_pad",
            "t_id",
            "t_allws",
            "t_mixed",
            "t_empty",
            "rp_dots",
            "rp_grow",
            "rp_none",
            "rp_empty_from",
        ] {
            assert_eq!(run_i64(&wasm, n, &[]).unwrap(), 1, "{n}");
        }
    }

    /// first / last return Option<T> (None on empty), consumed with
    /// OptionMatch — the safe list ends without a trapping ListGet.
    #[test]
    fn the_stdlib_first_and_last() {
        let nums = |vs: &[i64]| ExprSpec::List(vs.iter().copied().map(num).collect());
        let opt_or = |call_e: ExprSpec| ExprSpec::OptionMatch {
            opt: Box::new(call_e),
            some_bind: "v".into(),
            some_body: Box::new(r("v")),
            none_body: Box::new(num(-1)),
        };
        let nf = |name: &str, result: ExprSpec| FunctionSpec {
            name: name.into(),
            type_params: vec![],
            params: vec![],
            produces: ext(Type::Number),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result,
        };
        let mut fns = list_functions();
        fns.extend([
            nf("f_hit", opt_or(call("first", vec![nums(&[7, 8, 9])]))), // 7
            nf("f_miss", opt_or(call("first", vec![empty(Type::Number)]))), // -1
            nf("l_hit", opt_or(call("last", vec![nums(&[7, 8, 9])]))), // 9
            nf("l_one", opt_or(call("last", vec![nums(&[5])]))),       // 5
            nf("l_miss", opt_or(call("last", vec![empty(Type::Number)]))), // -1
        ]);
        let e = Editor::new(Store::open_in_memory().unwrap());
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "stdopt".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);
        let wasm = lower(e.store(), &m).unwrap();
        assert_eq!(run_i64(&wasm, "f_hit", &[]).unwrap(), 7);
        assert_eq!(run_i64(&wasm, "f_miss", &[]).unwrap(), -1);
        assert_eq!(run_i64(&wasm, "l_hit", &[]).unwrap(), 9);
        assert_eq!(run_i64(&wasm, "l_one", &[]).unwrap(), 5);
        assert_eq!(run_i64(&wasm, "l_miss", &[]).unwrap(), -1);
    }

    /// opt_map (Some(f v)|None) and opt_then (monadic bind: f v|None).
    #[test]
    fn the_stdlib_opt_map_and_then() {
        let lam = |params: Vec<(&str, Type)>, body: ExprSpec| ExprSpec::Lambda {
            params: params
                .into_iter()
                .map(|(n, t)| (n.to_string(), t))
                .collect(),
            body: Box::new(body),
        };
        let bin = |op, a: ExprSpec, b: ExprSpec| ExprSpec::BinOp {
            op,
            lhs: Box::new(a),
            rhs: Box::new(b),
        };
        let som = |v: ExprSpec| ExprSpec::OptionSome(Box::new(v));
        let non = || ExprSpec::OptionNone { elem: Type::Number };
        let unwrap = |o: ExprSpec| ExprSpec::OptionMatch {
            opt: Box::new(o),
            some_bind: "v".into(),
            some_body: Box::new(r("v")),
            none_body: Box::new(num(-1)),
        };
        let dbl = || lam(vec![("x", Type::Number)], bin(BinOp::Mul, r("x"), num(2)));
        // pos10: x -> if x > 0 then Some(x*10) else None
        let pos10 = || {
            lam(
                vec![("x", Type::Number)],
                ExprSpec::If {
                    cond: Box::new(bin(BinOp::Gt, r("x"), num(0))),
                    then_branch: Box::new(som(bin(BinOp::Mul, r("x"), num(10)))),
                    else_branch: Box::new(non()),
                },
            )
        };
        let nf = |name: &str, result: ExprSpec| FunctionSpec {
            name: name.into(),
            type_params: vec![],
            params: vec![],
            produces: ext(Type::Number),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result,
        };
        let mut fns = list_functions();
        fns.extend([
            nf("m_some", unwrap(call("opt_map", vec![dbl(), som(num(5))]))), // 10
            nf("m_none", unwrap(call("opt_map", vec![dbl(), non()]))),       // -1
            nf("t_some", unwrap(call("opt_then", vec![pos10(), som(num(3))]))), // 30
            nf("t_zero", unwrap(call("opt_then", vec![pos10(), som(num(-1))]))), // -1
            nf("t_none", unwrap(call("opt_then", vec![pos10(), non()]))),    // -1
        ]);
        let e = Editor::new(Store::open_in_memory().unwrap());
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "stdoptm".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);
        let wasm = lower(e.store(), &m).unwrap();
        assert_eq!(run_i64(&wasm, "m_some", &[]).unwrap(), 10);
        assert_eq!(run_i64(&wasm, "m_none", &[]).unwrap(), -1);
        assert_eq!(run_i64(&wasm, "t_some", &[]).unwrap(), 30);
        assert_eq!(run_i64(&wasm, "t_zero", &[]).unwrap(), -1);
        assert_eq!(run_i64(&wasm, "t_none", &[]).unwrap(), -1);
    }

    /// iabs / imin / imax / clamp (clamp composed from imin∘imax).
    #[test]
    fn the_stdlib_integer_helpers() {
        let nf = |name: &str, result: ExprSpec| FunctionSpec {
            name: name.into(),
            type_params: vec![],
            params: vec![],
            produces: ext(Type::Number),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result,
        };
        let mut fns = list_functions();
        fns.extend([
            nf("ab_neg", call("iabs", vec![num(-7)])),       // 7
            nf("ab_pos", call("iabs", vec![num(3)])),        // 3
            nf("mn", call("imin", vec![num(2), num(5)])),    // 2
            nf("mx", call("imax", vec![num(2), num(5)])),    // 5
            nf("c_hi", call("clamp", vec![num(10), num(0), num(5)])), // 5
            nf("c_lo", call("clamp", vec![num(-3), num(0), num(5)])), // 0
            nf("c_in", call("clamp", vec![num(3), num(0), num(5)])),  // 3
        ]);
        let e = Editor::new(Store::open_in_memory().unwrap());
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "stdnum".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);
        let wasm = lower(e.store(), &m).unwrap();
        for (n, want) in [
            ("ab_neg", 7),
            ("ab_pos", 3),
            ("mn", 2),
            ("mx", 5),
            ("c_hi", 5),
            ("c_lo", 0),
            ("c_in", 3),
        ] {
            assert_eq!(run_i64(&wasm, n, &[]).unwrap(), want, "{n}");
        }
    }

    /// ipow (exp<=0 → 1) and gcd (Euclid, sign-normalised).
    #[test]
    fn the_stdlib_ipow_and_gcd() {
        let nf = |name: &str, result: ExprSpec| FunctionSpec {
            name: name.into(),
            type_params: vec![],
            params: vec![],
            produces: ext(Type::Number),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result,
        };
        let mut fns = list_functions();
        fns.extend([
            nf("p_2_10", call("ipow", vec![num(2), num(10)])), // 1024
            nf("p_5_0", call("ipow", vec![num(5), num(0)])),   // 1
            nf("p_3_3", call("ipow", vec![num(3), num(3)])),   // 27
            nf("p_neg", call("ipow", vec![num(7), num(-1)])),  // 1
            nf("g_12_8", call("gcd", vec![num(12), num(8)])),  // 4
            nf("g_54_24", call("gcd", vec![num(54), num(24)])), // 6
            nf("g_7_0", call("gcd", vec![num(7), num(0)])),    // 7
            nf("g_0_0", call("gcd", vec![num(0), num(0)])),    // 0
            nf("g_neg", call("gcd", vec![num(-12), num(8)])),  // 4
        ]);
        let e = Editor::new(Store::open_in_memory().unwrap());
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "stdpow".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);
        let wasm = lower(e.store(), &m).unwrap();
        for (n, want) in [
            ("p_2_10", 1024),
            ("p_5_0", 1),
            ("p_3_3", 27),
            ("p_neg", 1),
            ("g_12_8", 4),
            ("g_54_24", 6),
            ("g_7_0", 7),
            ("g_0_0", 0),
            ("g_neg", 4),
        ] {
            assert_eq!(run_i64(&wasm, n, &[]).unwrap(), want, "{n}");
        }
    }

    /// decimal_round_str: half-up (away from zero) to N (0..4) places,
    /// formatted; composed from clamp/ipow/iabs/lpad0.
    #[test]
    fn decimal_round_str_formats() {
        let probe = |name: &str, v: f64, places: i64, want: &str| FunctionSpec {
            name: name.into(),
            type_params: vec![],
            params: vec![],
            produces: ext(Type::Bool),
            requires: BTreeSet::new(),
            on_failure: vec![],
            steps: vec![],
            result: ExprSpec::StrEq(
                Box::new(call(
                    "decimal_round_str",
                    vec![ExprSpec::Decimal(v), num(places)],
                )),
                Box::new(ExprSpec::Str(want.into())),
            ),
        };
        let cases = [
            ("a", 1.25, 1, "1.3"),
            ("b", 1.24, 1, "1.2"),
            ("c", 19.99, 1, "20.0"),
            ("d", 1.255, 2, "1.26"),
            ("e", -1.255, 2, "-1.26"),
            ("f", 2.5, 0, "3"),
            ("g", 1.4, 0, "1"),
            ("h", 1.2345, 4, "1.2345"),
            ("i", 0.0, 2, "0.00"),
        ];
        let mut fns = list_functions();
        fns.extend(cases.iter().map(|(n, v, pl, w)| probe(n, *v, *pl, w)));
        let e = Editor::new(Store::open_in_memory().unwrap());
        let (m, report) = e
            .apply_module(&ModuleSpec {
                name: "stddr".into(),
                types: vec![],
                functions: fns,
            })
            .unwrap();
        assert!(report.ok(), "violations: {:?}", report.violations);
        let wasm = lower(e.store(), &m).unwrap();
        for (n, _, _, w) in cases {
            assert_eq!(
                run_i64(&wasm, n, &[]).unwrap(),
                1,
                "decimal_round_str should produce {w}"
            );
        }
    }
}