type checking and error handling for builtins improved.

builtins/assert.go

@@ -1,6 +1,9 @@
 package builtins
 
-import "monkey/object"
+import (
+	"monkey/object"
+	"monkey/typing"
+)
 
 import (
 	"fmt"
@@ -9,17 +12,12 @@ import (
 
 // Assert ...
 func Assert(args ...object.Object) object.Object {
-	if len(args) != 2 {
-		return newError("wrong number of arguments. got=%d, want=2",
-			len(args))
-	}
-	if args[0].Type() != object.BOOLEAN_OBJ {
-		return newError("argument #1 to `assert` must be BOOLEAN, got %s",
-			args[0].Type())
-	}
-	if args[1].Type() != object.STRING_OBJ {
-		return newError("argument #2 to `assert` must be STRING, got %s",
-			args[0].Type())
+	if err := typing.Check(
+		"assert", args,
+		typing.ExactArgs(2),
+		typing.WithTypes(object.BOOLEAN_OBJ, object.STRING_OBJ),
+	); err != nil {
+		return newError(err.Error())
 	}
 
 	if !args[0].(*object.Boolean).Value {