rearrange builtins

builtins/str.go

@@ -0,0 +1,21 @@
+package builtins
+
+import "monkey/object"
+
+import (
+	"fmt"
+)
+
+// Str ...
+func Str(args ...object.Object) object.Object {
+	if len(args) != 1 {
+		return newError("wrong number of arguments. got=%d, want=1", len(args))
+	}
+
+	arg, ok := args[0].(fmt.Stringer)
+	if !ok {
+		return newError("argument to `str` not supported, got %s", args[0].Type())
+	}
+
+	return &object.String{Value: arg.String()}
+}