Struct ReadonlyParams 

pub struct ReadonlyParams {
    pub readonly: HashMap<Symbol, HashSet<Symbol>>,
}

Readonly parameter analysis result.

Maps each function to the set of its Seq<T> parameters that are never structurally mutated (no Push, Pop, Add, Remove, SetIndex, or reassignment) either directly or transitively through callees.

Parameters in this set are eligible for &[T] borrow in codegen instead of requiring ownership or cloning.

Safety under Rc (reference) semantics

LogosSeq is Rc<RefCell<Vec>>. The analysis is safe because:

• Let mutable X be param is caught by collect_consumed_params, which removes the param from the readonly set. This prevents aliasing where a mutable local could mutate through the shared Rc.
• Interior mutation via Rc clone requires the mutable keyword on the alias, which triggers the consumed-param check.
• Fixed-point propagation through the callgraph catches transitive mutations: if a callee mutates a param position, all callers passing a readonly candidate to that position lose their readonly status.

Fields

readonly: HashMap<Symbol, HashSet<Symbol>>

fn_sym → set of param symbols that are readonly within that function.

Implementations

impl ReadonlyParams

pub fn analyze( stmts: &[Stmt<'_>], callgraph: &CallGraph, type_env: &TypeEnv, ) -> ReadonlyParams

Analyze the program and compute readonly parameters.

Uses fixed-point iteration: starts optimistically with all Seq<T> params as readonly candidates, then eliminates those that are directly mutated or transitively mutated via callee propagation.

Native functions are trusted: their params remain readonly unless the LOGOS body explicitly mutates them (which is impossible since they have no body).

pub fn is_readonly(&self, fn_sym: Symbol, param_sym: Symbol) -> bool

Returns true if param_sym is readonly within fn_sym.