1 files changed, 13 insertions, 1 deletions
diff --git a/std.py b/std.py
index 1393acf..26c6793 100644
--- a/std.py
+++ b/std.py
@@ -66,6 +66,13 @@ def std_if(cond, t_branch, f_branch):
         ret = evaluate_expression(f_branch)
     return ret
 
+# type validation
+def std_is_string(arg):
+    if isinstance(arg, NebString):
+        return NebBool(True)
+    else:
+        return NebBool(False)
+
 def evaluate_expression(expr):
     if not expr.symbol.name in STD:
         raise Exception(f"no such symbol: {expr.symbol.name}")
@@ -83,6 +90,7 @@ def evaluate_expression(expr):
             if isinstance(in_sig[idx], sig[idx]):
                 validated += 1
         if validated == len(sig):
+            print(f"{value.func.args}")
             ret = value.impl(*(expr.args))
             return ret
 
@@ -122,7 +130,11 @@ def build_std():
     STD["concat"] = [concat_string_string]
 
     # flow control
-    if_bool_expr_expr = FuncImpl(NebFunction("if", [NebBool, NebExpression, NebExpression], NebType.ANY), std_if)
+    if_bool_expr_expr = FuncImpl(NebFunction("if", [NebBool, NebExpression, NebExpression], NebAny), std_if)
     STD["if"] = [if_bool_expr_expr]
 
+    # type checking
+    is_string = FuncImpl(NebFunction("string?", [NebAny], NebBool), std_is_string)
+    STD["string?"] = [is_string]
+
 build_std()