local variables

4 files changed, 25 insertions, 3 deletions

diff --git a/src/ast.c b/src/ast.c
index 5460c87..83a55c6 100644
--- a/src/ast.c
+++ b/src/ast.c
@@ -88,6 +88,15 @@ ASTNode *ast_rop(ROp rop, ASTNode *aexp1, ASTNode *aexp2) {
   return node;
 }
 
+ASTNode *ast_let(ASTNode *var, ASTNode *aexp, ASTNode *stm) {
+  ASTNode *node = new_node(NT_LET);
+  node->u.d_let.var = var;
+  node->u.d_let.aexp = aexp;
+  node->u.d_let.stm = stm;
+  return node;
+}
+
+
 void ast_free(ASTNode *node) {
   if (!node) return;
   switch (node->type) {
diff --git a/src/interpreter.c b/src/interpreter.c
index 93b1bdb..4449847 100644
--- a/src/interpreter.c
+++ b/src/interpreter.c
@@ -76,9 +76,9 @@ void exec_stmt(hashmap_t context, ASTNode *node) {
       case NT_SKIP:
         return;
       case NT_ASSIGN: {
-        char *var = node->u.d_assign.var->u.d_var.name;
+        char *name = node->u.d_assign.var->u.d_var.name;
         int val = eval_aexpr(context, node->u.d_assign.aexp);
-        context_set(context, var, val);
+        context_set(context, name, val);
         return;
       }
       case NT_SEQ:
@@ -96,6 +96,15 @@ void exec_stmt(hashmap_t context, ASTNode *node) {
           exec_stmt(context, node->u.d_while.stm);
         }
         return;
+      case NT_LET: {
+        char *name = node->u.d_let.var->u.d_var.name;
+        int old_val = context_get(context, name);
+        int new_val = eval_aexpr(context, node->u.d_let.aexp);
+        context_set(context, name, new_val);
+        exec_stmt(context, node->u.d_let.stm);
+        context_set(context, name, old_val);
+        return;
+      }
       default:
         fprintf(stderr, "Bad stmt node %d\n", node->type);
         exit(EXIT_FAILURE);
diff --git a/src/lexer.l b/src/lexer.l
index c9aaff0..26ac229 100644
--- a/src/lexer.l
+++ b/src/lexer.l
@@ -17,6 +17,8 @@ WHITESPACE  [ \t\r\n]+
 "end"           { return TOKEN_END; }
 "while"         { return TOKEN_WHILE; }
 "do"            { return TOKEN_DO; }
+"var"           { return TOKEN_VAR; }
+"in"            { return TOKEN_IN; }
 
 "("             { return TOKEN_LEFT_PARENTHESIS; }
 ")"             { return TOKEN_RIGHT_PARENTHESIS; }
diff --git a/src/parser.y b/src/parser.y
index 9a94480..cb3544e 100644
--- a/src/parser.y
+++ b/src/parser.y
@@ -29,7 +29,7 @@ void yyerror(const char *s) {
 %token       TOKEN_LEFT_PARENTHESIS TOKEN_RIGHT_PARENTHESIS
 %token       TOKEN_SEMICOLON
 %token       TOKEN_SKIP
-%token       TOKEN_IF TOKEN_THEN TOKEN_ELSE TOKEN_END TOKEN_WHILE TOKEN_DO
+%token       TOKEN_IF TOKEN_THEN TOKEN_ELSE TOKEN_END TOKEN_WHILE TOKEN_DO TOKEN_VAR TOKEN_IN
 %token       TOKEN_PLUS TOKEN_MINUS TOKEN_MULTIPLY
 %token       TOKEN_NOT TOKEN_OR TOKEN_AND
 %token       TOKEN_EQUALS TOKEN_NOT_EQUALS TOKEN_LESS_THAN TOKEN_LESS_EQUAL TOKEN_GREATER_THAN TOKEN_GREATER_EQUAL
@@ -54,6 +54,8 @@ statement             : TOKEN_SKIP
                         { $$ = ast_if($2, $4, $6); }
                       | TOKEN_WHILE boolean_expression TOKEN_DO statement TOKEN_END
                         { $$ = ast_while($2, $4); }
+                      | TOKEN_VAR variable TOKEN_ASSIGN arithmetic_expression TOKEN_IN statement TOKEN_END
+                        { $$ = ast_let($2, $4, $6); }
                       ;
 
 variable              : TOKEN_IDENTIFIER