type checking and error handling for builtins improved.

builtins/bool.go

@@ -1,40 +1,18 @@
 package builtins
 
-import "monkey/object"
+import (
+	"monkey/object"
+	"monkey/typing"
+)
 
 // Bool ...
 func Bool(args ...object.Object) object.Object {
-	if len(args) != 1 {
-		return newError("wrong number of arguments. got=%d, want=1", len(args))
+	if err := typing.Check(
+		"bool", args,
+		typing.ExactArgs(1),
+	); err != nil {
+		return newError(err.Error())
 	}
 
-	switch arg := args[0].(type) {
-	case *object.Null:
-		return &object.Boolean{Value: false}
-	case *object.Boolean:
-		return arg
-	case *object.Integer:
-		if arg.Value == 0 {
-			return &object.Boolean{Value: false}
-		}
-		return &object.Boolean{Value: true}
-	case *object.String:
-		if len(arg.Value) > 0 {
-			return &object.Boolean{Value: true}
-		}
-		return &object.Boolean{Value: false}
-	case *object.Array:
-		if len(arg.Elements) > 0 {
-			return &object.Boolean{Value: true}
-		}
-		return &object.Boolean{Value: false}
-	case *object.Hash:
-		if len(arg.Pairs) > 0 {
-			return &object.Boolean{Value: true}
-		}
-		return &object.Boolean{Value: false}
-
-	default:
-		return newError("argument to `bool` not supported, got=%s", args[0].Type())
-	}
+	return &object.Boolean{Value: args[0].Bool()}
 }