cl-interpret: Make an attempt at closures

(It kinda sucks, but it emulates closures half decently)

compiler/cl-interpret/src/function/collect_upvars.rs

@@ -0,0 +1,105 @@
+//! Collects the "Upvars" of a function at the point of its creation, allowing variable capture
+use crate::{convalue::ConValue, env::Environment};
+use cl_ast::{ast_visitor::visit::*, Function, Let, Param, Path, PathPart, Sym};
+use std::collections::{HashMap, HashSet};
+
+pub fn collect_upvars(f: &Function, env: &Environment) -> super::Upvars {
+    CollectUpvars::new(env).get_upvars(f)
+}
+
+#[derive(Clone, Debug)]
+pub struct CollectUpvars<'env> {
+    env: &'env Environment,
+    upvars: HashMap<Sym, Option<ConValue>>,
+    blacklist: HashSet<Sym>,
+}
+
+impl<'env> CollectUpvars<'env> {
+    pub fn new(env: &'env Environment) -> Self {
+        Self { upvars: HashMap::new(), blacklist: HashSet::new(), env }
+    }
+    pub fn get_upvars(mut self, f: &cl_ast::Function) -> HashMap<Sym, Option<ConValue>> {
+        self.visit_function(f);
+        self.upvars
+    }
+
+    pub fn add_upvar(&mut self, name: &Sym) {
+        let Self { env, upvars, blacklist } = self;
+        if blacklist.contains(name) || upvars.contains_key(name) {
+            return;
+        }
+        if let Ok(upvar) = env.get(*name) {
+            upvars.insert(*name, Some(upvar));
+        }
+    }
+
+    pub fn bind_name(&mut self, name: &Sym) {
+        self.blacklist.insert(*name);
+    }
+}
+
+impl<'env, 'a> Visit<'a> for CollectUpvars<'env> {
+    fn visit_block(&mut self, b: &'a cl_ast::Block) {
+        let blacklist = self.blacklist.clone();
+
+        // visit the block
+        let cl_ast::Block { stmts } = b;
+        stmts.iter().for_each(|s| self.visit_stmt(s));
+
+        // restore the blacklist
+        self.blacklist = blacklist;
+    }
+
+    fn visit_let(&mut self, l: &'a cl_ast::Let) {
+        let Let { mutable, name, ty, init } = l;
+        self.visit_mutability(mutable);
+        if let Some(ty) = ty {
+            self.visit_ty(ty);
+        }
+        // visit the initializer, which may use the bound name
+        if let Some(init) = init {
+            self.visit_expr(init)
+        }
+        // a bound name can never be an upvar
+        self.blacklist.insert(*name);
+    }
+
+    fn visit_function(&mut self, f: &'a cl_ast::Function) {
+        let Function { name: _, sign: _, bind, body } = f;
+        // parameters can never be upvars
+        for Param { mutability: _, name } in bind {
+            self.bind_name(name);
+        }
+        if let Some(body) = body {
+            self.visit_block(body);
+        }
+    }
+
+    fn visit_for(&mut self, f: &'a cl_ast::For) {
+        let cl_ast::For { bind, cond, pass, fail } = f;
+        self.visit_expr(cond);
+        self.visit_else(fail);
+        self.bind_name(bind); // TODO: is bind only bound in the pass block?
+        self.visit_block(pass);
+    }
+
+    fn visit_path(&mut self, p: &'a cl_ast::Path) {
+        // TODO: path resolution in environments
+        let Path { absolute: false, parts } = p else {
+            return;
+        };
+        let [PathPart::Ident(name)] = parts.as_slice() else {
+            return;
+        };
+        self.add_upvar(name);
+    }
+
+    fn visit_fielder(&mut self, f: &'a cl_ast::Fielder) {
+        let cl_ast::Fielder { name, init } = f;
+        if let Some(init) = init {
+            self.visit_expr(init);
+        } else {
+            self.add_upvar(name); // fielder without init grabs from env
+        }
+    }
+}