cljrs_runtime/interp/

syntax_quote.rs

//! Syntax-quote (backtick) expansion.
//!
//! Syntax-quote is evaluated directly to a `Value`, rather than being
//! expanded to intermediate AST and then evaluated.

use crate::builtins::SPECIAL_FORMS;
use crate::builtins::form::{expand_reader_conds_cow, form_to_value, select_reader_cond};
use crate::env::env::Env;
use crate::env::error::{EvalError, EvalResult};
use cljrs_gc::GcPtr;
use cljrs_reader::Form;
use cljrs_reader::form::FormKind;
use cljrs_value::value::SetValue;
use cljrs_value::{Keyword, PersistentList, PersistentVector, Symbol, Value};
use std::sync::Arc;
use std::sync::atomic::{AtomicU64, Ordering};

static GENSYM_COUNTER: AtomicU64 = AtomicU64::new(0);

/// Expand a syntax-quoted form to a Value.
pub fn syntax_quote(form: &Form, env: &mut Env) -> EvalResult {
    let mut gensyms = std::collections::HashMap::new();
    sq_form(form, env, &mut gensyms)
}

fn sq_form(
    form: &Form,
    env: &mut Env,
    gensyms: &mut std::collections::HashMap<String, Arc<str>>,
) -> EvalResult {
    match &form.kind {
        // ~expr — evaluate normally.
        FormKind::Unquote(inner) => crate::interp::eval::eval(inner, env),

        // ~@expr at top level is an error.
        FormKind::UnquoteSplice(_) => Err(EvalError::Runtime(
            "splice-unquote outside list/vector context".into(),
        )),

        // Symbols: auto-qualify with current namespace; auto-gensym `foo#`.
        FormKind::Symbol(s) => {
            let qualified = qualify_symbol(s, env, gensyms);
            Ok(Value::symbol(Symbol::parse(&qualified)))
        }

        // Atoms: return as quoted values.
        FormKind::Nil => Ok(Value::Nil),
        FormKind::Bool(b) => Ok(Value::Bool(*b)),
        FormKind::Int(n) => Ok(Value::Long(*n)),
        FormKind::Float(f) => Ok(Value::Double(*f)),
        FormKind::Str(s) => Ok(Value::string(s.clone())),
        FormKind::Char(c) => Ok(Value::Char(*c)),
        FormKind::Keyword(s) => Ok(Value::keyword(Keyword::parse(s))),
        FormKind::AutoKeyword(s) => {
            let full = env
                .globals
                .resolve_auto_keyword(&env.current_ns, s)
                .map_err(EvalError::Runtime)?;
            Ok(Value::keyword(Keyword::parse(&full)))
        }
        FormKind::AutoSymbol(s) => {
            let full = env
                .globals
                .resolve_auto_keyword(&env.current_ns, s)
                .map_err(EvalError::Runtime)?;
            Ok(Value::symbol(Symbol::parse(&full)))
        }

        // Lists: process each element, splicing ~@ items.
        FormKind::List(forms) => {
            let parts = sq_seq(forms, env, gensyms)?;
            // Concatenate segments.
            let mut out: Vec<Value> = Vec::new();
            for part in parts {
                match part {
                    Segment::One(v) => out.push(v),
                    Segment::Many(vs) => out.extend(vs),
                }
            }
            Ok(Value::List(GcPtr::new(PersistentList::from_iter(out))))
        }

        // Vectors: process each element, splicing ~@ items.
        FormKind::Vector(forms) => {
            let parts = sq_seq(forms, env, gensyms)?;
            let mut out: Vec<Value> = Vec::new();
            for part in parts {
                match part {
                    Segment::One(v) => out.push(v),
                    Segment::Many(vs) => out.extend(vs),
                }
            }
            Ok(Value::Vector(GcPtr::new(PersistentVector::from_iter(out))))
        }

        // Maps: treat flat k/v pairs like a sequence.
        FormKind::Map(forms) => {
            let parts = sq_seq(forms, env, gensyms)?;
            let mut out: Vec<Value> = Vec::new();
            for part in parts {
                match part {
                    Segment::One(v) => out.push(v),
                    Segment::Many(vs) => out.extend(vs),
                }
            }
            if !out.len().is_multiple_of(2) {
                return Err(EvalError::Runtime(
                    "syntax-quote map requires even number of forms".into(),
                ));
            }
            let mut m = cljrs_value::MapValue::empty();
            for pair in out.chunks(2) {
                m = m.assoc(pair[0].clone(), pair[1].clone());
            }
            Ok(Value::Map(m))
        }

        // Sets.
        FormKind::Set(forms) => {
            let parts = sq_seq(forms, env, gensyms)?;
            let mut out: Vec<Value> = Vec::new();
            for part in parts {
                match part {
                    Segment::One(v) => out.push(v),
                    Segment::Many(vs) => out.extend(vs),
                }
            }
            let set = out
                .into_iter()
                .fold(cljrs_value::PersistentHashSet::empty(), |s, v| s.conj(v));
            Ok(Value::Set(SetValue::Hash(GcPtr::new(set))))
        }

        // `'inner` inside syntax-quote: recursively process `inner` so that
        // unquotes like `'~x` work — they evaluate x and wrap the result in (quote ...).
        FormKind::Quote(inner) => {
            let processed = sq_form(inner, env, gensyms)?;
            Ok(Value::List(GcPtr::new(PersistentList::from_iter([
                Value::symbol(Symbol::simple("quote")),
                processed,
            ]))))
        }

        // `#?(...)` in a non-sibling position: syntax-quote the selected branch.
        FormKind::ReaderCond {
            splicing: false,
            clauses,
        } => match select_reader_cond(clauses) {
            Some(selected) => sq_form(selected, env, gensyms),
            None => Ok(Value::Nil),
        },

        // `#?@(...)` here has no sibling sequence to splice into.
        FormKind::ReaderCond { splicing: true, .. } => Err(EvalError::Runtime(
            "splicing reader conditional not in a sequence context".into(),
        )),

        // #(...) anonymous function: expand to (fn* [...] ...) then syntax-quote.
        FormKind::AnonFn(body) => {
            let expanded = crate::builtins::form::expand_anon_fn(body, form.span.clone());
            sq_form(&expanded, env, gensyms)
        }

        // Everything else: wrap as literal data.
        _other => form_to_value(form),
    }
}

enum Segment {
    One(Value),
    Many(Vec<Value>),
}

/// Process a sibling sequence, resolving `#?`/`#?@` for `:rust` first so a
/// splice contributes its branch elements to the enclosing collection.
fn sq_seq(
    forms: &[Form],
    env: &mut Env,
    gensyms: &mut std::collections::HashMap<String, Arc<str>>,
) -> EvalResult<Vec<Segment>> {
    let forms = expand_reader_conds_cow(forms);
    let mut out = Vec::with_capacity(forms.len());
    for f in forms.iter() {
        match &f.kind {
            FormKind::UnquoteSplice(inner) => {
                // ~@expr: evaluate and spread.
                let v = crate::interp::eval::eval(inner, env)?;
                let items = crate::interp::destructure::value_to_seq_vec(&v);
                out.push(Segment::Many(items));
            }
            _ => {
                let v = sq_form(f, env, gensyms)?;
                out.push(Segment::One(v));
            }
        }
    }
    Ok(out)
}

/// Qualify a symbol name for use inside syntax-quote.
///
/// - `foo#` → unique gensym `foo__N__auto__` (same N within one backtick).
/// - `alias/foo` → resolved through the current ns's `:require :as` aliases
///   to `real-ns/foo`, exactly like `::alias/kw` and `(binding [alias/*x*
///   ...])`; not just kept as-is, since call sites (e.g. protocol-metadata
///   dispatch) key on the *resolved* qualified symbol, not the alias text.
/// - Special literals (`nil`, `true`, `false`) → kept as-is.
/// - Special forms (`def`, `if`, `try`, `catch`, `let`, …) → kept as-is.
/// - Symbols that resolve in the current namespace → qualified with resolved ns.
/// - Everything else → `current-ns/name`.
fn qualify_symbol(
    s: &str,
    env: &Env,
    gensyms: &mut std::collections::HashMap<String, Arc<str>>,
) -> String {
    // Already qualified (but not the bare `/` division symbol, or a
    // dangling/leading slash — neither has a real ns part to resolve).
    if let Some(idx) = s.find('/') {
        if idx > 0 && idx < s.len() - 1 {
            let (ns_part, name_part) = (&s[..idx], &s[idx + 1..]);
            let resolved_ns = env
                .globals
                .resolve_alias(&env.current_ns, ns_part)
                .unwrap_or_else(|| Arc::from(ns_part));
            return format!("{resolved_ns}/{name_part}");
        }
        return s.to_string();
    }
    // Special literals.
    if matches!(s, "nil" | "true" | "false") {
        return s.to_string();
    }
    // Auto-gensym: `foo#`.
    if let Some(base) = s.strip_suffix('#') {
        let generated = gensyms.entry(s.to_string()).or_insert_with(|| {
            let n = crate::env::policy::next_transaction_gensym()
                .unwrap_or_else(|| GENSYM_COUNTER.fetch_add(1, Ordering::Relaxed));
            Arc::from(format!("{base}__{n}__auto__"))
        });
        return generated.as_ref().to_string();
    }
    // Special forms and try-related tokens: never qualify.
    if SPECIAL_FORMS.contains(&s)
        || matches!(s, "catch" | "finally" | "Exception" | "Throwable" | "Error")
    {
        return s.to_string();
    }
    // Resolve through current namespace (interns and refers).
    // If the symbol resolves to a var, use that var's actual namespace.
    if let Some(var_ptr) = env.globals.lookup_var_in_ns(&env.current_ns, s) {
        let var_ns = var_ptr.get().namespace.as_ref().to_string();
        return format!("{var_ns}/{s}");
    }
    // Default: qualify with current namespace.
    format!("{}/{}", env.current_ns, s)
}