type checking and error handling for builtins improved.

typing/typing.go

@@ -0,0 +1,56 @@
+package typing
+
+import (
+	"fmt"
+	"monkey/object"
+)
+
+type CheckFunc func(name string, args []object.Object) error
+
+func Check(name string, args []object.Object, checks ...CheckFunc) error {
+	for _, check := range checks {
+		if err := check(name, args); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func ExactArgs(n int) CheckFunc {
+	return func(name string, args []object.Object) error {
+		if len(args) != n {
+			return fmt.Errorf("TypeError: %s() takes exactly %d argument (%d given)", name, n, len(args))
+		}
+		return nil
+	}
+}
+
+func MinimumArgs(n int) CheckFunc {
+	return func(name string, args []object.Object) error {
+		if len(args) < n {
+			return fmt.Errorf("TypeError: %s() takes a minimum %d arguments (%d given)", name, n, len(args))
+		}
+		return nil
+	}
+}
+
+func RangeOfArgs(n, m int) CheckFunc {
+	return func(name string, args []object.Object) error {
+		if len(args) < n || len(args) > m {
+			return fmt.Errorf("TypeError: %s() takes at least %d arguments at most %d (%d given)", name, n, m, len(args))
+		}
+		return nil
+	}
+}
+
+func WithTypes(types ...object.ObjectType) CheckFunc {
+	return func(name string, args []object.Object) error {
+		for i, t := range types {
+			if i < len(args) && args[i].Type() != t {
+				return fmt.Errorf("TypeError: %s() expected argument #%d to be `%s` got `%s`", name, i+1, t, args[i].Type())
+			}
+		}
+		return nil
+	}
+}