From e3d8e031c6f20c68f2227028ee8b3e73cd9b8161 Mon Sep 17 00:00:00 2001
From: Johnny Richard <johnny@johnnyrichard.com>
Date: Mon, 1 May 2023 01:57:22 +0200
Subject: parser: Implement variable assignment

This commit introduces variable assignment making it possible to
change a variable value. Example:

  myvar: i32 = 1;
  myvar = 2;

Signed-off-by: Johnny Richard <johnny@johnnyrichard.com>
Co-authored-by: Carlos Maniero <carlos@maniero.me>
---
 src/parser.c | 94 +++++++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 81 insertions(+), 13 deletions(-)

(limited to 'src/parser.c')

diff --git a/src/parser.c b/src/parser.c
index af372fb..ad0fdc9 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -235,6 +235,40 @@ parser_parse_return_stmt(parser_t *parser, ast_node_t *node)
   return true;
 }
 
+static bool
+parser_parse_variable_assignment(parser_t *parser, token_t variable_token, ast_node_t *node)
+{
+  if (!drop_expected_token(parser, TOKEN_EQUAL))
+    return false;
+
+  ast_node_t *expression = ast_node_new();
+
+  if (!parser_parse_expression(parser, expression) || !drop_expected_token(parser, TOKEN_SEMICOLON)) {
+    ast_node_destroy(expression);
+    return false;
+  }
+
+  ast_node_t *variable_declaration_node = scope_get(parser->scope, variable_token.value);
+
+  if (variable_declaration_node == NULL) {
+    parser_error_t error;
+    error.token = variable_token;
+
+    sprintf(error.message, "trying to assign '" SVFMT "' before defining it.", SVARG(&variable_token.value));
+
+    parser->errors[parser->errors_len++] = error;
+    return false;
+  }
+
+  assert(variable_declaration_node->kind == AST_VARIABLE_DECLARATION);
+
+  node->kind = AST_VARIABLE_ASSIGNMENT;
+  node->data = (ast_node_data_t){ .variable_assignment = {
+                                    .identifier = &variable_declaration_node->data.variable_declaration.identifier,
+                                    .expression = expression } };
+  return true;
+}
+
 static bool
 parser_parse_variable_definition(parser_t *parser, string_view_t variable_name, ast_node_t *node)
 {
@@ -268,9 +302,12 @@ parser_parse_block_declarations(parser_t *parser, vector_t *body)
   token_t current_token;
   lexer_next_token(parser->lexer, &current_token);
 
+  scope_enter(parser->scope);
+
   while (current_token.kind != TOKEN_CCURLY && current_token.kind != TOKEN_EOF) {
     if (current_token.kind != TOKEN_NAME) {
       parser_error_push_unexpected_kind(parser, &current_token, TOKEN_NAME);
+      scope_leave(parser->scope);
       return false;
     }
 
@@ -280,20 +317,53 @@ parser_parse_block_declarations(parser_t *parser, vector_t *body)
 
       if (!parsed_return) {
         ast_node_destroy(return_node);
+        scope_leave(parser->scope);
         return false;
       }
 
       vector_push_back(body, return_node);
     } else {
-      ast_node_t *variable_node = ast_node_new();
-      bool parsed_variable = parser_parse_variable_definition(parser, current_token.value, variable_node);
-
-      if (!parsed_variable) {
-        ast_node_destroy(variable_node);
-        return false;
+      token_t token;
+      lexer_peek_next_token(parser->lexer, &token);
+
+      switch (token.kind) {
+        case TOKEN_COLON: {
+          ast_node_t *variable_node = ast_node_new();
+
+          if (!parser_parse_variable_definition(parser, current_token.value, variable_node)) {
+            ast_node_destroy(variable_node);
+            return false;
+          }
+
+          vector_push_back(body, variable_node);
+          break;
+        }
+        case TOKEN_EQUAL: {
+          ast_node_t *variable_assignment = ast_node_new();
+
+          if (!parser_parse_variable_assignment(parser, current_token, variable_assignment)) {
+            ast_node_destroy(variable_assignment);
+            return false;
+          }
+
+          vector_push_back(body, variable_assignment);
+          break;
+        }
+        case TOKEN_NAME:
+        case TOKEN_OPAREN:
+        case TOKEN_CPAREN:
+        case TOKEN_SEMICOLON:
+        case TOKEN_OCURLY:
+        case TOKEN_CCURLY:
+        case TOKEN_NUMBER:
+        case TOKEN_PLUS:
+        case TOKEN_MINUS:
+        case TOKEN_STAR:
+        case TOKEN_SLASH:
+        case TOKEN_EOF:
+        case TOKEN_UNKNOWN:
+          break;
       }
-
-      vector_push_back(body, variable_node);
     }
 
     lexer_next_token(parser->lexer, &current_token);
@@ -301,6 +371,7 @@ parser_parse_block_declarations(parser_t *parser, vector_t *body)
 
   if (current_token.kind != TOKEN_CCURLY) {
     parser_error_push_unexpected_kind(parser, &current_token, TOKEN_CCURLY);
+    scope_leave(parser->scope);
     return false;
   }
 
@@ -313,8 +384,10 @@ parser_parse_block_declarations(parser_t *parser, vector_t *body)
     sprintf(error.message, "expected 'return' keyword.");
 
     parser->errors[parser->errors_len++] = error;
+    scope_leave(parser->scope);
     return false;
   }
+  scope_leave(parser->scope);
   return true;
 }
 
@@ -347,14 +420,9 @@ parser_parse_function_declaration(parser_t *parser, ast_node_t *node)
   ast_node_init_function_declaration(node, func_name_token.value, return_type, body);
   scope_push(parser->scope, &node->data.function.identifier, node);
 
-  scope_enter(parser->scope);
-
   if (!parser_parse_block_declarations(parser, body)) {
-    scope_leave(parser->scope);
     return false;
   }
 
-  scope_leave(parser->scope);
-
   return true;
 }
-- 
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