Move function logic into functions files

3 files changed, 379 insertions, 371 deletions

diff --git a/src/compile.c b/src/compile.c
index c906112b..fa47e63c 100644
--- a/src/compile.c
+++ b/src/compile.c
@@ -54,289 +54,6 @@ Text_t compile_maybe_incref(env_t *env, ast_t *ast, type_t *t) {
     return compile_to_type(env, ast, t);
 }
 
-static void add_closed_vars(Table_t *closed_vars, env_t *enclosing_scope, env_t *env, ast_t *ast) {
-    if (ast == NULL) return;
-
-    switch (ast->tag) {
-    case Var: {
-        binding_t *b = get_binding(enclosing_scope, Match(ast, Var)->name);
-        if (b) {
-            binding_t *shadow = get_binding(env, Match(ast, Var)->name);
-            if (!shadow || shadow == b) Table$str_set(closed_vars, Match(ast, Var)->name, b);
-        }
-        break;
-    }
-    case TextJoin: {
-        for (ast_list_t *child = Match(ast, TextJoin)->children; child; child = child->next)
-            add_closed_vars(closed_vars, enclosing_scope, env, child->ast);
-        break;
-    }
-    case Declare: {
-        ast_t *value = Match(ast, Declare)->value;
-        add_closed_vars(closed_vars, enclosing_scope, env, value);
-        bind_statement(env, ast);
-        break;
-    }
-    case Assign: {
-        for (ast_list_t *target = Match(ast, Assign)->targets; target; target = target->next)
-            add_closed_vars(closed_vars, enclosing_scope, env, target->ast);
-        for (ast_list_t *value = Match(ast, Assign)->values; value; value = value->next)
-            add_closed_vars(closed_vars, enclosing_scope, env, value->ast);
-        break;
-    }
-    case BINOP_CASES: {
-        binary_operands_t binop = BINARY_OPERANDS(ast);
-        add_closed_vars(closed_vars, enclosing_scope, env, binop.lhs);
-        add_closed_vars(closed_vars, enclosing_scope, env, binop.rhs);
-        break;
-    }
-    case Not:
-    case Negative:
-    case HeapAllocate:
-    case StackReference: {
-        // UNSAFE:
-        ast_t *value = ast->__data.Not.value;
-        // END UNSAFE
-        add_closed_vars(closed_vars, enclosing_scope, env, value);
-        break;
-    }
-    case Min: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Min)->lhs);
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Min)->rhs);
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Min)->key);
-        break;
-    }
-    case Max: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Max)->lhs);
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Max)->rhs);
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Max)->key);
-        break;
-    }
-    case List: {
-        for (ast_list_t *item = Match(ast, List)->items; item; item = item->next)
-            add_closed_vars(closed_vars, enclosing_scope, env, item->ast);
-        break;
-    }
-    case Set: {
-        for (ast_list_t *item = Match(ast, Set)->items; item; item = item->next)
-            add_closed_vars(closed_vars, enclosing_scope, env, item->ast);
-        break;
-    }
-    case Table: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Table)->default_value);
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Table)->fallback);
-        for (ast_list_t *entry = Match(ast, Table)->entries; entry; entry = entry->next)
-            add_closed_vars(closed_vars, enclosing_scope, env, entry->ast);
-        break;
-    }
-    case TableEntry: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, TableEntry)->key);
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, TableEntry)->value);
-        break;
-    }
-    case Comprehension: {
-        DeclareMatch(comp, ast, Comprehension);
-        if (comp->expr->tag == Comprehension) { // Nested comprehension
-            ast_t *body = comp->filter ? WrapAST(ast, If, .condition = comp->filter, .body = comp->expr) : comp->expr;
-            ast_t *loop = WrapAST(ast, For, .vars = comp->vars, .iter = comp->iter, .body = body);
-            return add_closed_vars(closed_vars, enclosing_scope, env, loop);
-        }
-
-        // List/Set/Table comprehension:
-        ast_t *body = comp->expr;
-        if (comp->filter) body = WrapAST(comp->expr, If, .condition = comp->filter, .body = body);
-        ast_t *loop = WrapAST(ast, For, .vars = comp->vars, .iter = comp->iter, .body = body);
-        add_closed_vars(closed_vars, enclosing_scope, env, loop);
-        break;
-    }
-    case Lambda: {
-        DeclareMatch(lambda, ast, Lambda);
-        env_t *lambda_scope = fresh_scope(env);
-        for (arg_ast_t *arg = lambda->args; arg; arg = arg->next)
-            set_binding(lambda_scope, arg->name, get_arg_ast_type(env, arg), Texts("_$", arg->name));
-        add_closed_vars(closed_vars, enclosing_scope, lambda_scope, lambda->body);
-        break;
-    }
-    case FunctionCall: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, FunctionCall)->fn);
-        for (arg_ast_t *arg = Match(ast, FunctionCall)->args; arg; arg = arg->next)
-            add_closed_vars(closed_vars, enclosing_scope, env, arg->value);
-        break;
-    }
-    case MethodCall: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, MethodCall)->self);
-        for (arg_ast_t *arg = Match(ast, MethodCall)->args; arg; arg = arg->next)
-            add_closed_vars(closed_vars, enclosing_scope, env, arg->value);
-        break;
-    }
-    case Block: {
-        env = fresh_scope(env);
-        for (ast_list_t *statement = Match(ast, Block)->statements; statement; statement = statement->next)
-            add_closed_vars(closed_vars, enclosing_scope, env, statement->ast);
-        break;
-    }
-    case For: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, For)->iter);
-        env_t *body_scope = for_scope(env, ast);
-        add_closed_vars(closed_vars, enclosing_scope, body_scope, Match(ast, For)->body);
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, For)->empty);
-        break;
-    }
-    case While: {
-        DeclareMatch(while_, ast, While);
-        add_closed_vars(closed_vars, enclosing_scope, env, while_->condition);
-        env_t *scope = fresh_scope(env);
-        add_closed_vars(closed_vars, enclosing_scope, scope, while_->body);
-        break;
-    }
-    case If: {
-        DeclareMatch(if_, ast, If);
-        ast_t *condition = if_->condition;
-        if (condition->tag == Declare) {
-            env_t *truthy_scope = fresh_scope(env);
-            bind_statement(truthy_scope, condition);
-            if (!Match(condition, Declare)->value)
-                code_err(condition, "This declared variable must have an initial value");
-            add_closed_vars(closed_vars, enclosing_scope, env, Match(condition, Declare)->value);
-            ast_t *var = Match(condition, Declare)->var;
-            type_t *cond_t = get_type(truthy_scope, var);
-            if (cond_t->tag == OptionalType) {
-                set_binding(truthy_scope, Match(var, Var)->name, Match(cond_t, OptionalType)->type, EMPTY_TEXT);
-            }
-            add_closed_vars(closed_vars, enclosing_scope, truthy_scope, if_->body);
-            add_closed_vars(closed_vars, enclosing_scope, env, if_->else_body);
-        } else {
-            add_closed_vars(closed_vars, enclosing_scope, env, condition);
-            env_t *truthy_scope = env;
-            type_t *cond_t = get_type(env, condition);
-            if (condition->tag == Var && cond_t->tag == OptionalType) {
-                truthy_scope = fresh_scope(env);
-                set_binding(truthy_scope, Match(condition, Var)->name, Match(cond_t, OptionalType)->type, EMPTY_TEXT);
-            }
-            add_closed_vars(closed_vars, enclosing_scope, truthy_scope, if_->body);
-            add_closed_vars(closed_vars, enclosing_scope, env, if_->else_body);
-        }
-        break;
-    }
-    case When: {
-        DeclareMatch(when, ast, When);
-        add_closed_vars(closed_vars, enclosing_scope, env, when->subject);
-        type_t *subject_t = get_type(env, when->subject);
-
-        if (subject_t->tag != EnumType) {
-            for (when_clause_t *clause = when->clauses; clause; clause = clause->next) {
-                add_closed_vars(closed_vars, enclosing_scope, env, clause->pattern);
-                add_closed_vars(closed_vars, enclosing_scope, env, clause->body);
-            }
-
-            if (when->else_body) add_closed_vars(closed_vars, enclosing_scope, env, when->else_body);
-            return;
-        }
-
-        DeclareMatch(enum_t, subject_t, EnumType);
-        for (when_clause_t *clause = when->clauses; clause; clause = clause->next) {
-            const char *clause_tag_name;
-            if (clause->pattern->tag == Var) clause_tag_name = Match(clause->pattern, Var)->name;
-            else if (clause->pattern->tag == FunctionCall && Match(clause->pattern, FunctionCall)->fn->tag == Var)
-                clause_tag_name = Match(Match(clause->pattern, FunctionCall)->fn, Var)->name;
-            else code_err(clause->pattern, "This is not a valid pattern for a ", type_to_str(subject_t), " enum");
-
-            type_t *tag_type = NULL;
-            for (tag_t *tag = enum_t->tags; tag; tag = tag->next) {
-                if (streq(tag->name, clause_tag_name)) {
-                    tag_type = tag->type;
-                    break;
-                }
-            }
-            assert(tag_type);
-            env_t *scope = when_clause_scope(env, subject_t, clause);
-            add_closed_vars(closed_vars, enclosing_scope, scope, clause->body);
-        }
-        if (when->else_body) add_closed_vars(closed_vars, enclosing_scope, env, when->else_body);
-        break;
-    }
-    case Repeat: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Repeat)->body);
-        break;
-    }
-    case Reduction: {
-        DeclareMatch(reduction, ast, Reduction);
-        static int64_t next_id = 1;
-        ast_t *item = FakeAST(Var, String("$it", next_id++));
-        ast_t *loop =
-            FakeAST(For, .vars = new (ast_list_t, .ast = item), .iter = reduction->iter, .body = FakeAST(Pass));
-        env_t *scope = for_scope(env, loop);
-        add_closed_vars(closed_vars, enclosing_scope, scope, reduction->key ? reduction->key : item);
-        break;
-    }
-    case Defer: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Defer)->body);
-        break;
-    }
-    case Return: {
-        ast_t *ret = Match(ast, Return)->value;
-        if (ret) add_closed_vars(closed_vars, enclosing_scope, env, ret);
-        break;
-    }
-    case Index: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Index)->indexed);
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Index)->index);
-        break;
-    }
-    case FieldAccess: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, FieldAccess)->fielded);
-        break;
-    }
-    case Optional: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Optional)->value);
-        break;
-    }
-    case NonOptional: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, NonOptional)->value);
-        break;
-    }
-    case DocTest: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, DocTest)->expr);
-        break;
-    }
-    case Assert: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Assert)->expr);
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Assert)->message);
-        break;
-    }
-    case Deserialize: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Deserialize)->value);
-        break;
-    }
-    case ExplicitlyTyped: {
-        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, ExplicitlyTyped)->ast);
-        break;
-    }
-    case Use:
-    case FunctionDef:
-    case ConvertDef:
-    case StructDef:
-    case EnumDef:
-    case LangDef:
-    case Extend: {
-        errx(1, "Definitions should not be reachable in a closure.");
-    }
-    default: break;
-    }
-}
-
-static Table_t get_closed_vars(env_t *env, arg_ast_t *args, ast_t *block) {
-    env_t *body_scope = fresh_scope(env);
-    for (arg_ast_t *arg = args; arg; arg = arg->next) {
-        type_t *arg_type = get_arg_ast_type(env, arg);
-        set_binding(body_scope, arg->name, arg_type, Texts("_$", arg->name));
-    }
-
-    Table_t closed_vars = {};
-    add_closed_vars(&closed_vars, env, body_scope, block);
-    return closed_vars;
-}
-
 Text_t compile_declaration(type_t *t, Text_t name) {
     if (t->tag == FunctionType) {
         DeclareMatch(fn, t, FunctionType);
@@ -2236,94 +1953,7 @@ Text_t compile(env_t *env, ast_t *ast) {
         if (base->tag == TableEntry) return compile(env, WrapAST(ast, Table, .entries = new (ast_list_t, .ast = ast)));
         else return compile(env, WrapAST(ast, List, .items = new (ast_list_t, .ast = ast)));
     }
-    case Lambda: {
-        DeclareMatch(lambda, ast, Lambda);
-        Text_t name = namespace_name(env, env->namespace, Texts("lambda$", String(lambda->id)));
-
-        env_t *body_scope = fresh_scope(env);
-        body_scope->deferred = NULL;
-        for (arg_ast_t *arg = lambda->args; arg; arg = arg->next) {
-            type_t *arg_type = get_arg_ast_type(env, arg);
-            set_binding(body_scope, arg->name, arg_type, Texts("_$", arg->name));
-        }
-
-        type_t *ret_t = get_type(body_scope, lambda->body);
-        if (ret_t->tag == ReturnType) ret_t = Match(ret_t, ReturnType)->ret;
-
-        if (lambda->ret_type) {
-            type_t *declared = parse_type_ast(env, lambda->ret_type);
-            if (can_promote(ret_t, declared)) ret_t = declared;
-            else
-                code_err(ast, "This function was declared to return a value of type ", type_to_str(declared),
-                         ", but actually returns a value of type ", type_to_str(ret_t));
-        }
-
-        body_scope->fn_ret = ret_t;
-
-        Table_t closed_vars = get_closed_vars(env, lambda->args, ast);
-        if (Table$length(closed_vars) > 0) { // Create a typedef for the lambda's closure userdata
-            Text_t def = Text("typedef struct {");
-            for (int64_t i = 0; i < closed_vars.entries.length; i++) {
-                struct {
-                    const char *name;
-                    binding_t *b;
-                } *entry = closed_vars.entries.data + closed_vars.entries.stride * i;
-                if (has_stack_memory(entry->b->type))
-                    code_err(ast, "This function is holding onto a reference to ", type_to_str(entry->b->type),
-                             " stack memory in the variable `", entry->name,
-                             "`, but the function may outlive the stack memory");
-                if (entry->b->type->tag == ModuleType) continue;
-                set_binding(body_scope, entry->name, entry->b->type, Texts("userdata->", entry->name));
-                def = Texts(def, compile_declaration(entry->b->type, Text$from_str(entry->name)), "; ");
-            }
-            def = Texts(def, "} ", name, "$userdata_t;");
-            env->code->local_typedefs = Texts(env->code->local_typedefs, def);
-        }
-
-        Text_t code = Texts("static ", compile_type(ret_t), " ", name, "(");
-        for (arg_ast_t *arg = lambda->args; arg; arg = arg->next) {
-            type_t *arg_type = get_arg_ast_type(env, arg);
-            code = Texts(code, compile_type(arg_type), " _$", arg->name, ", ");
-        }
-
-        Text_t userdata;
-        if (Table$length(closed_vars) == 0) {
-            code = Texts(code, "void *_)");
-            userdata = Text("NULL");
-        } else {
-            userdata = Texts("new(", name, "$userdata_t");
-            for (int64_t i = 0; i < closed_vars.entries.length; i++) {
-                struct {
-                    const char *name;
-                    binding_t *b;
-                } *entry = closed_vars.entries.data + closed_vars.entries.stride * i;
-                if (entry->b->type->tag == ModuleType) continue;
-                binding_t *b = get_binding(env, entry->name);
-                assert(b);
-                Text_t binding_code = b->code;
-                if (entry->b->type->tag == ListType) userdata = Texts(userdata, ", LIST_COPY(", binding_code, ")");
-                else if (entry->b->type->tag == TableType || entry->b->type->tag == SetType)
-                    userdata = Texts(userdata, ", TABLE_COPY(", binding_code, ")");
-                else userdata = Texts(userdata, ", ", binding_code);
-            }
-            userdata = Texts(userdata, ")");
-            code = Texts(code, name, "$userdata_t *userdata)");
-        }
-
-        Text_t body = EMPTY_TEXT;
-        for (ast_list_t *stmt = Match(lambda->body, Block)->statements; stmt; stmt = stmt->next) {
-            if (stmt->next || ret_t->tag == VoidType || ret_t->tag == AbortType
-                || get_type(body_scope, stmt->ast)->tag == ReturnType)
-                body = Texts(body, compile_statement(body_scope, stmt->ast), "\n");
-            else body = Texts(body, compile_statement(body_scope, FakeAST(Return, stmt->ast)), "\n");
-            bind_statement(body_scope, stmt->ast);
-        }
-        if ((ret_t->tag == VoidType || ret_t->tag == AbortType) && body_scope->deferred)
-            body = Texts(body, compile_statement(body_scope, FakeAST(Return)), "\n");
-
-        env->code->lambdas = Texts(env->code->lambdas, code, " {\n", body, "\n}\n");
-        return Texts("((Closure_t){", name, ", ", userdata, "})");
-    }
+    case Lambda: return compile_lambda(env, ast);
     case MethodCall: {
         DeclareMatch(call, ast, MethodCall);
         type_t *self_t = get_type(env, call->self);
diff --git a/src/compile/functions.c b/src/compile/functions.c
index 1a2e5d3d..4015f0ca 100644
--- a/src/compile/functions.c
+++ b/src/compile/functions.c
@@ -1,6 +1,8 @@
+#include "functions.h"
 #include "../ast.h"
 #include "../compile.h"
 #include "../environment.h"
+#include "../naming.h"
 #include "../stdlib/datatypes.h"
 #include "../stdlib/integers.h"
 #include "../stdlib/nums.h"
@@ -195,3 +197,377 @@ Text_t compile_function_call(env_t *env, ast_t *ast) {
         code_err(call->fn, "This is not a function, it's a ", type_to_str(fn_t));
     }
 }
+
+public
+Text_t compile_lambda(env_t *env, ast_t *ast) {
+    DeclareMatch(lambda, ast, Lambda);
+    Text_t name = namespace_name(env, env->namespace, Texts("lambda$", String(lambda->id)));
+
+    env_t *body_scope = fresh_scope(env);
+    body_scope->deferred = NULL;
+    for (arg_ast_t *arg = lambda->args; arg; arg = arg->next) {
+        type_t *arg_type = get_arg_ast_type(env, arg);
+        set_binding(body_scope, arg->name, arg_type, Texts("_$", arg->name));
+    }
+
+    type_t *ret_t = get_type(body_scope, lambda->body);
+    if (ret_t->tag == ReturnType) ret_t = Match(ret_t, ReturnType)->ret;
+
+    if (lambda->ret_type) {
+        type_t *declared = parse_type_ast(env, lambda->ret_type);
+        if (can_promote(ret_t, declared)) ret_t = declared;
+        else
+            code_err(ast, "This function was declared to return a value of type ", type_to_str(declared),
+                     ", but actually returns a value of type ", type_to_str(ret_t));
+    }
+
+    body_scope->fn_ret = ret_t;
+
+    Table_t closed_vars = get_closed_vars(env, lambda->args, ast);
+    if (Table$length(closed_vars) > 0) { // Create a typedef for the lambda's closure userdata
+        Text_t def = Text("typedef struct {");
+        for (int64_t i = 0; i < closed_vars.entries.length; i++) {
+            struct {
+                const char *name;
+                binding_t *b;
+            } *entry = closed_vars.entries.data + closed_vars.entries.stride * i;
+            if (has_stack_memory(entry->b->type))
+                code_err(ast, "This function is holding onto a reference to ", type_to_str(entry->b->type),
+                         " stack memory in the variable `", entry->name,
+                         "`, but the function may outlive the stack memory");
+            if (entry->b->type->tag == ModuleType) continue;
+            set_binding(body_scope, entry->name, entry->b->type, Texts("userdata->", entry->name));
+            def = Texts(def, compile_declaration(entry->b->type, Text$from_str(entry->name)), "; ");
+        }
+        def = Texts(def, "} ", name, "$userdata_t;");
+        env->code->local_typedefs = Texts(env->code->local_typedefs, def);
+    }
+
+    Text_t code = Texts("static ", compile_type(ret_t), " ", name, "(");
+    for (arg_ast_t *arg = lambda->args; arg; arg = arg->next) {
+        type_t *arg_type = get_arg_ast_type(env, arg);
+        code = Texts(code, compile_type(arg_type), " _$", arg->name, ", ");
+    }
+
+    Text_t userdata;
+    if (Table$length(closed_vars) == 0) {
+        code = Texts(code, "void *_)");
+        userdata = Text("NULL");
+    } else {
+        userdata = Texts("new(", name, "$userdata_t");
+        for (int64_t i = 0; i < closed_vars.entries.length; i++) {
+            struct {
+                const char *name;
+                binding_t *b;
+            } *entry = closed_vars.entries.data + closed_vars.entries.stride * i;
+            if (entry->b->type->tag == ModuleType) continue;
+            binding_t *b = get_binding(env, entry->name);
+            assert(b);
+            Text_t binding_code = b->code;
+            if (entry->b->type->tag == ListType) userdata = Texts(userdata, ", LIST_COPY(", binding_code, ")");
+            else if (entry->b->type->tag == TableType || entry->b->type->tag == SetType)
+                userdata = Texts(userdata, ", TABLE_COPY(", binding_code, ")");
+            else userdata = Texts(userdata, ", ", binding_code);
+        }
+        userdata = Texts(userdata, ")");
+        code = Texts(code, name, "$userdata_t *userdata)");
+    }
+
+    Text_t body = EMPTY_TEXT;
+    for (ast_list_t *stmt = Match(lambda->body, Block)->statements; stmt; stmt = stmt->next) {
+        if (stmt->next || ret_t->tag == VoidType || ret_t->tag == AbortType
+            || get_type(body_scope, stmt->ast)->tag == ReturnType)
+            body = Texts(body, compile_statement(body_scope, stmt->ast), "\n");
+        else body = Texts(body, compile_statement(body_scope, FakeAST(Return, stmt->ast)), "\n");
+        bind_statement(body_scope, stmt->ast);
+    }
+    if ((ret_t->tag == VoidType || ret_t->tag == AbortType) && body_scope->deferred)
+        body = Texts(body, compile_statement(body_scope, FakeAST(Return)), "\n");
+
+    env->code->lambdas = Texts(env->code->lambdas, code, " {\n", body, "\n}\n");
+    return Texts("((Closure_t){", name, ", ", userdata, "})");
+}
+
+static void add_closed_vars(Table_t *closed_vars, env_t *enclosing_scope, env_t *env, ast_t *ast) {
+    if (ast == NULL) return;
+
+    switch (ast->tag) {
+    case Var: {
+        binding_t *b = get_binding(enclosing_scope, Match(ast, Var)->name);
+        if (b) {
+            binding_t *shadow = get_binding(env, Match(ast, Var)->name);
+            if (!shadow || shadow == b) Table$str_set(closed_vars, Match(ast, Var)->name, b);
+        }
+        break;
+    }
+    case TextJoin: {
+        for (ast_list_t *child = Match(ast, TextJoin)->children; child; child = child->next)
+            add_closed_vars(closed_vars, enclosing_scope, env, child->ast);
+        break;
+    }
+    case Declare: {
+        ast_t *value = Match(ast, Declare)->value;
+        add_closed_vars(closed_vars, enclosing_scope, env, value);
+        bind_statement(env, ast);
+        break;
+    }
+    case Assign: {
+        for (ast_list_t *target = Match(ast, Assign)->targets; target; target = target->next)
+            add_closed_vars(closed_vars, enclosing_scope, env, target->ast);
+        for (ast_list_t *value = Match(ast, Assign)->values; value; value = value->next)
+            add_closed_vars(closed_vars, enclosing_scope, env, value->ast);
+        break;
+    }
+    case BINOP_CASES: {
+        binary_operands_t binop = BINARY_OPERANDS(ast);
+        add_closed_vars(closed_vars, enclosing_scope, env, binop.lhs);
+        add_closed_vars(closed_vars, enclosing_scope, env, binop.rhs);
+        break;
+    }
+    case Not:
+    case Negative:
+    case HeapAllocate:
+    case StackReference: {
+        // UNSAFE:
+        ast_t *value = ast->__data.Not.value;
+        // END UNSAFE
+        add_closed_vars(closed_vars, enclosing_scope, env, value);
+        break;
+    }
+    case Min: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Min)->lhs);
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Min)->rhs);
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Min)->key);
+        break;
+    }
+    case Max: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Max)->lhs);
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Max)->rhs);
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Max)->key);
+        break;
+    }
+    case List: {
+        for (ast_list_t *item = Match(ast, List)->items; item; item = item->next)
+            add_closed_vars(closed_vars, enclosing_scope, env, item->ast);
+        break;
+    }
+    case Set: {
+        for (ast_list_t *item = Match(ast, Set)->items; item; item = item->next)
+            add_closed_vars(closed_vars, enclosing_scope, env, item->ast);
+        break;
+    }
+    case Table: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Table)->default_value);
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Table)->fallback);
+        for (ast_list_t *entry = Match(ast, Table)->entries; entry; entry = entry->next)
+            add_closed_vars(closed_vars, enclosing_scope, env, entry->ast);
+        break;
+    }
+    case TableEntry: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, TableEntry)->key);
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, TableEntry)->value);
+        break;
+    }
+    case Comprehension: {
+        DeclareMatch(comp, ast, Comprehension);
+        if (comp->expr->tag == Comprehension) { // Nested comprehension
+            ast_t *body = comp->filter ? WrapAST(ast, If, .condition = comp->filter, .body = comp->expr) : comp->expr;
+            ast_t *loop = WrapAST(ast, For, .vars = comp->vars, .iter = comp->iter, .body = body);
+            return add_closed_vars(closed_vars, enclosing_scope, env, loop);
+        }
+
+        // List/Set/Table comprehension:
+        ast_t *body = comp->expr;
+        if (comp->filter) body = WrapAST(comp->expr, If, .condition = comp->filter, .body = body);
+        ast_t *loop = WrapAST(ast, For, .vars = comp->vars, .iter = comp->iter, .body = body);
+        add_closed_vars(closed_vars, enclosing_scope, env, loop);
+        break;
+    }
+    case Lambda: {
+        DeclareMatch(lambda, ast, Lambda);
+        env_t *lambda_scope = fresh_scope(env);
+        for (arg_ast_t *arg = lambda->args; arg; arg = arg->next)
+            set_binding(lambda_scope, arg->name, get_arg_ast_type(env, arg), Texts("_$", arg->name));
+        add_closed_vars(closed_vars, enclosing_scope, lambda_scope, lambda->body);
+        break;
+    }
+    case FunctionCall: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, FunctionCall)->fn);
+        for (arg_ast_t *arg = Match(ast, FunctionCall)->args; arg; arg = arg->next)
+            add_closed_vars(closed_vars, enclosing_scope, env, arg->value);
+        break;
+    }
+    case MethodCall: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, MethodCall)->self);
+        for (arg_ast_t *arg = Match(ast, MethodCall)->args; arg; arg = arg->next)
+            add_closed_vars(closed_vars, enclosing_scope, env, arg->value);
+        break;
+    }
+    case Block: {
+        env = fresh_scope(env);
+        for (ast_list_t *statement = Match(ast, Block)->statements; statement; statement = statement->next)
+            add_closed_vars(closed_vars, enclosing_scope, env, statement->ast);
+        break;
+    }
+    case For: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, For)->iter);
+        env_t *body_scope = for_scope(env, ast);
+        add_closed_vars(closed_vars, enclosing_scope, body_scope, Match(ast, For)->body);
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, For)->empty);
+        break;
+    }
+    case While: {
+        DeclareMatch(while_, ast, While);
+        add_closed_vars(closed_vars, enclosing_scope, env, while_->condition);
+        env_t *scope = fresh_scope(env);
+        add_closed_vars(closed_vars, enclosing_scope, scope, while_->body);
+        break;
+    }
+    case If: {
+        DeclareMatch(if_, ast, If);
+        ast_t *condition = if_->condition;
+        if (condition->tag == Declare) {
+            env_t *truthy_scope = fresh_scope(env);
+            bind_statement(truthy_scope, condition);
+            if (!Match(condition, Declare)->value)
+                code_err(condition, "This declared variable must have an initial value");
+            add_closed_vars(closed_vars, enclosing_scope, env, Match(condition, Declare)->value);
+            ast_t *var = Match(condition, Declare)->var;
+            type_t *cond_t = get_type(truthy_scope, var);
+            if (cond_t->tag == OptionalType) {
+                set_binding(truthy_scope, Match(var, Var)->name, Match(cond_t, OptionalType)->type, EMPTY_TEXT);
+            }
+            add_closed_vars(closed_vars, enclosing_scope, truthy_scope, if_->body);
+            add_closed_vars(closed_vars, enclosing_scope, env, if_->else_body);
+        } else {
+            add_closed_vars(closed_vars, enclosing_scope, env, condition);
+            env_t *truthy_scope = env;
+            type_t *cond_t = get_type(env, condition);
+            if (condition->tag == Var && cond_t->tag == OptionalType) {
+                truthy_scope = fresh_scope(env);
+                set_binding(truthy_scope, Match(condition, Var)->name, Match(cond_t, OptionalType)->type, EMPTY_TEXT);
+            }
+            add_closed_vars(closed_vars, enclosing_scope, truthy_scope, if_->body);
+            add_closed_vars(closed_vars, enclosing_scope, env, if_->else_body);
+        }
+        break;
+    }
+    case When: {
+        DeclareMatch(when, ast, When);
+        add_closed_vars(closed_vars, enclosing_scope, env, when->subject);
+        type_t *subject_t = get_type(env, when->subject);
+
+        if (subject_t->tag != EnumType) {
+            for (when_clause_t *clause = when->clauses; clause; clause = clause->next) {
+                add_closed_vars(closed_vars, enclosing_scope, env, clause->pattern);
+                add_closed_vars(closed_vars, enclosing_scope, env, clause->body);
+            }
+
+            if (when->else_body) add_closed_vars(closed_vars, enclosing_scope, env, when->else_body);
+            return;
+        }
+
+        DeclareMatch(enum_t, subject_t, EnumType);
+        for (when_clause_t *clause = when->clauses; clause; clause = clause->next) {
+            const char *clause_tag_name;
+            if (clause->pattern->tag == Var) clause_tag_name = Match(clause->pattern, Var)->name;
+            else if (clause->pattern->tag == FunctionCall && Match(clause->pattern, FunctionCall)->fn->tag == Var)
+                clause_tag_name = Match(Match(clause->pattern, FunctionCall)->fn, Var)->name;
+            else code_err(clause->pattern, "This is not a valid pattern for a ", type_to_str(subject_t), " enum");
+
+            type_t *tag_type = NULL;
+            for (tag_t *tag = enum_t->tags; tag; tag = tag->next) {
+                if (streq(tag->name, clause_tag_name)) {
+                    tag_type = tag->type;
+                    break;
+                }
+            }
+            assert(tag_type);
+            env_t *scope = when_clause_scope(env, subject_t, clause);
+            add_closed_vars(closed_vars, enclosing_scope, scope, clause->body);
+        }
+        if (when->else_body) add_closed_vars(closed_vars, enclosing_scope, env, when->else_body);
+        break;
+    }
+    case Repeat: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Repeat)->body);
+        break;
+    }
+    case Reduction: {
+        DeclareMatch(reduction, ast, Reduction);
+        static int64_t next_id = 1;
+        ast_t *item = FakeAST(Var, String("$it", next_id++));
+        ast_t *loop =
+            FakeAST(For, .vars = new (ast_list_t, .ast = item), .iter = reduction->iter, .body = FakeAST(Pass));
+        env_t *scope = for_scope(env, loop);
+        add_closed_vars(closed_vars, enclosing_scope, scope, reduction->key ? reduction->key : item);
+        break;
+    }
+    case Defer: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Defer)->body);
+        break;
+    }
+    case Return: {
+        ast_t *ret = Match(ast, Return)->value;
+        if (ret) add_closed_vars(closed_vars, enclosing_scope, env, ret);
+        break;
+    }
+    case Index: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Index)->indexed);
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Index)->index);
+        break;
+    }
+    case FieldAccess: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, FieldAccess)->fielded);
+        break;
+    }
+    case Optional: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Optional)->value);
+        break;
+    }
+    case NonOptional: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, NonOptional)->value);
+        break;
+    }
+    case DocTest: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, DocTest)->expr);
+        break;
+    }
+    case Assert: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Assert)->expr);
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Assert)->message);
+        break;
+    }
+    case Deserialize: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, Deserialize)->value);
+        break;
+    }
+    case ExplicitlyTyped: {
+        add_closed_vars(closed_vars, enclosing_scope, env, Match(ast, ExplicitlyTyped)->ast);
+        break;
+    }
+    case Use:
+    case FunctionDef:
+    case ConvertDef:
+    case StructDef:
+    case EnumDef:
+    case LangDef:
+    case Extend: {
+        errx(1, "Definitions should not be reachable in a closure.");
+    }
+    default: break;
+    }
+}
+
+public
+Table_t get_closed_vars(env_t *env, arg_ast_t *args, ast_t *block) {
+    env_t *body_scope = fresh_scope(env);
+    for (arg_ast_t *arg = args; arg; arg = arg->next) {
+        type_t *arg_type = get_arg_ast_type(env, arg);
+        set_binding(body_scope, arg->name, arg_type, Texts("_$", arg->name));
+    }
+
+    Table_t closed_vars = {};
+    add_closed_vars(&closed_vars, env, body_scope, block);
+    return closed_vars;
+}
diff --git a/src/compile/functions.h b/src/compile/functions.h
index fdab495f..f7edd2aa 100644
--- a/src/compile/functions.h
+++ b/src/compile/functions.h
@@ -5,3 +5,5 @@
 
 Text_t compile_function_call(env_t *env, ast_t *ast);
 Text_t compile_arguments(env_t *env, ast_t *call_ast, arg_t *spec_args, arg_ast_t *call_args);
+Text_t compile_lambda(env_t *env, ast_t *ast);
+Table_t get_closed_vars(env_t *env, arg_ast_t *args, ast_t *block);