From a921acd83750a66bcb73179ce1581f3280197289 Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Sat, 30 Oct 2021 14:59:44 +0200
Subject: Add symbol declaration error checking

---
 src/parser.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 75 insertions(+), 6 deletions(-)

diff --git a/src/parser.c b/src/parser.c
index 2429f68..3e6abc2 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -313,13 +313,28 @@ parse_list(Parser *parser, Errors *errors) {
     root->head = NULL;
     root->tail = NULL;
     Object *current = root;
+    bool first = true;
     while (has_next_token(parser)) {
+        Token tok = peek_token(parser);
         current->head = parse_tree(parser, errors);
         if (errors->n != 0 || current->head == NULL) {
             return NULL;
         }
 
-        Token tok = peek_token(parser);
+        if (first) {
+            if (!IS_SYMBOL(current->head) && !IS_LAMBDA(current->head)) {
+                error_push(errors, (Error){
+                    .type = ERR_TYPE_PARSER,
+                    .value = ERR_NOT_CALLABLE,
+                    .line = tok.line,
+                    .col = tok.col,
+                });
+                return NULL;
+            }
+            first = false;
+        }
+
+        tok = peek_token(parser);
         if (tok.type == TOKEN_RPAREN) {
             next_token(parser);
             return root;
@@ -388,9 +403,60 @@ parse_tree(Parser *parser, Errors *errors) {
     return NULL;
 }
 
+bool
+symbol_in_env(Environment *env, Object *symbol) {
+    while (env != NULL) {
+        Object *found = ht_lookup(env->table, symbol);
+        if (found != NULL) {
+            return true;
+        }
+        env = env->parent;
+    }
+    return false;
+}
+
 void
-scope_check(Environment *env) {
-    // STUB
+check_object_scope(Environment *env, Object *obj, Errors *errors) {
+    if (obj == NULL) {
+        return;
+    }
+    switch (obj->type) {
+        case OBJ_TYPE_SYMBOL: {
+            if (!symbol_in_env(env, obj)) {
+                error_push(errors, (Error){
+                    .type = ERR_TYPE_PARSER,
+                    .value = ERR_SYMBOL_NOT_FOUND,
+                    .line = obj->line,
+                    .col = obj->col,
+                });
+            }
+        } break;
+        case OBJ_TYPE_PAIR: {
+            check_object_scope(env, obj->head, errors);
+            check_object_scope(env, obj->tail, errors);
+        } break;
+        case OBJ_TYPE_DEF: {
+            ht_insert(env->table, obj->var_name, obj->var_expr);
+            check_object_scope(env, obj->var_expr, errors);
+        } break;
+        case OBJ_TYPE_SET: {
+            check_object_scope(env, obj->var_name, errors);
+            check_object_scope(env, obj->var_expr, errors);
+        } break;
+        case OBJ_TYPE_IF: {
+            check_object_scope(env, obj->condition, errors);
+            check_object_scope(env, obj->expr_true, errors);
+            check_object_scope(env, obj->expr_false, errors);
+        } break;
+        case OBJ_TYPE_LAMBDA: {
+            Environment *new_env = env_alloc(env);
+            for (size_t i = 0; i < array_size(obj->body); i++) {
+                Object *expr = obj->body[i];
+                check_object_scope(new_env, expr, errors);
+            }
+        } break;
+        default: break;
+    }
 }
 
 Root *
@@ -428,9 +494,12 @@ parse(Token *tokens, Errors *errors) {
         ht_insert(global_env->table, symbol, symbol);
     }
 
-    // Perform semantic analysis.
-    scope_check(global_env);
-    // TODO: Check that symbols are defined before usage.
+    // Check that symbols are defined before usage.
+    for (size_t i = 0; i < array_size(roots); i++) {
+        Object *root = roots[i];
+        check_object_scope(global_env, root, errors);
+    }
+
     // TODO: Remove unnecessary statements.
     return roots;
 }
-- 
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