type checking and error handling for builtins improved.

builtins/write.go

@@ -1,33 +1,27 @@
 package builtins
 
-import "monkey/object"
-
 import (
-	"os"
+	"io/ioutil"
+	"monkey/object"
+	"monkey/typing"
 )
 
 // Write ...
 func Write(args ...object.Object) object.Object {
-	if len(args) != 2 {
-		return newError("wrong number of arguments. got=%d, want=2",
-			len(args))
+	if err := typing.Check(
+		"write", args,
+		typing.ExactArgs(2),
+		typing.WithTypes(object.STRING_OBJ, object.STRING_OBJ),
+	); err != nil {
+		return newError(err.Error())
 	}
 
-	arg, ok := args[0].(*object.String)
-	if !ok {
-		return newError("argument #1 to `write` expected to be `str` got=%T", args[0].Type())
-	}
-	filename := arg.Value
+	filename := args[0].(*object.String).Value
+	data := []byte(args[1].(*object.String).Value)
 
-	arg, ok = args[1].(*object.String)
-	if !ok {
-		return newError("argument #2 to `write` expected to be `str` got=%T", args[1].Type())
-	}
-	data := []byte(arg.Value)
-
-	err := os.WriteFile(filename, data, 0755)
+	err := ioutil.WriteFile(filename, data, 0755)
 	if err != nil {
-		return newError("error writing file: %s", err)
+		return newError("IOError: error writing file %s: %s", filename, err)
 	}
 
 	return &object.Null{}