Add syntax sugar for let.

src/parser.c

@@ -411,6 +411,47 @@ libab_result _parse_fun_param(struct parser_state* state, libab_tree** store_int
     return result;
 }
 
+libab_result _parse_def_fun(struct parser_state* state, libab_tree** store_into) {
+    libab_result result = LIBAB_SUCCESS;
+    libab_tree* temp;
+    if(_parser_is_type(state, TOKEN_KW_LET)) {
+        _parser_state_step(state);
+        if(!_parser_eof(state)) {
+            result = _parser_construct_node_both(state, state->current_match, store_into);
+        } else {
+            result = LIBAB_UNEXPECTED;
+        }
+    } else {
+        result = LIBAB_UNEXPECTED;
+    }
+
+    if(result == LIBAB_SUCCESS) {
+        _parser_state_step(state);
+        (*store_into)->parse_type = NULL;
+        (*store_into)->variant = TREE_FUN;
+        result = _parser_consume_char(state, ':');
+    }
+
+    if(result == LIBAB_SUCCESS) {
+        result = _parse_type(state, &(*store_into)->parse_type);
+    }
+
+    if(result == LIBAB_SUCCESS) {
+        result = _parser_consume_type(state, TOKEN_KW_BE);
+    }
+
+    if(result == LIBAB_SUCCESS) {
+        PARSE_CHILD(result, state, _parse_expression, temp, &(*store_into)->children);
+    }
+
+    if(result != LIBAB_SUCCESS && *store_into) {
+        libab_tree_free_recursive(*store_into);
+        *store_into = NULL;
+    }
+
+    return result;
+}
+
 libab_result _parse_fun(struct parser_state* state, libab_tree** store_into) {
     libab_result result = LIBAB_SUCCESS;
     int is_parenth, is_comma;
@@ -635,6 +676,8 @@ libab_result _parse_atom(struct parser_state* state, libab_tree** store_into) {
         result = _parse_braced_block(state, store_into);
     } else if(_parser_is_type(state, TOKEN_KW_FUN)) {
         result = _parse_fun(state, store_into);
+    } else if(_parser_is_type(state, TOKEN_KW_LET)) {
+        result = _parse_def_fun(state, store_into);
     } else if(_parser_is_type(state, TOKEN_KW_RETURN)) {
         result = _parse_return(state, store_into);
     } else {