feat(types): add reporter interface

types.ts

@@ -1,23 +1,41 @@
 // Copyright 2023-latest Tomoki Miyauchi. All rights reserved. MIT license.
 // This module is browser compatible.
 
+import { isString } from "./deps.ts";
+
 /** Validator API. */
-export interface Validator<In = unknown> {
+export interface Validator<In = unknown> extends Display {
   /** Validates the input and yield validation errors if exists. */
   validate: (input: In) => Iterable<ValidationError>;
 }
 
+export type Validation<In = unknown, In_ extends In = In> = In extends In_
+  ? Validator<In>
+  : AssertiveValidator<In, In_>;
+
+export interface Display {
+  toString(): string;
+}
+
+export interface Transformer<In = unknown, Out = In> {
+  transform: (input: In) => Out;
+}
+
+export interface Struct<In = unknown, In_ extends In = In, Out = unknown>
+  extends Iterable<Validator<In> | Transformer<In, Out>> {
+}
+
 /** Assert API for validated data type. */
-export interface Assert<In = unknown, Out extends In = In> {
-  [Assert.symbol]: Out;
+export interface Assert<T = unknown> {
+  [Assert.symbol]: T;
 }
 
 export class Assert {
-  static readonly symbol = Symbol("assert.type");
+  static readonly symbol: unique symbol;
 }
 
-export interface AssertiveValidator<In = unknown, Out extends In = In>
-  extends Assert<In, Out>, Validator<In> {}
+export interface AssertiveValidator<In = unknown, In_ extends In = In>
+  extends Validator<In>, Assert<In_> {}
 
 /** Validation error options. */
 export interface ValidationErrorOptions extends ErrorOptions {
@@ -41,8 +59,33 @@ export class ValidationError extends Error {
   }
 }
 
+export interface Reporter<T = unknown> {
+  report(context: T): string;
+
+  expect(message: string): this;
+  expect(report: Reporter["report"]): this;
+}
+
+export class Reporter<T = unknown> {
+  #messageFn?: Reporter<T>["report"];
+
+  report(context: T): string {
+    return this.#messageFn?.(context) ?? "";
+  }
+
+  expect(messageOrReport: string | Reporter<T>["report"]): this {
+    const fn = isString(messageOrReport)
+      ? (() => messageOrReport) as Reporter<T>["report"]
+      : messageOrReport;
+
+    this.#messageFn = fn;
+
+    return this;
+  }
+}
+
 /** Result of OK API. */
-export class Ok<T> {
+export class Ok<T = unknown> {
   /** Node type. */
   type: "ok" = "ok";
 
@@ -52,6 +95,16 @@ export class Ok<T> {
   constructor(data: T) {
     this.data = data;
   }
+
+  /** Whether the {@link Result} is {@link Ok} or not. */
+  isOk(): this is Ok<T> {
+    return true;
+  }
+
+  /** Whether the {@link Result} is {@link Err} or not. */
+  isErr(): this is Err {
+    return false;
+  }
 }
 
 /** Result of Error API. */
@@ -65,6 +118,16 @@ export class Err {
   constructor(errors: readonly ValidationError[]) {
     this.errors = errors;
   }
+
+  /** Whether the {@link Result} is {@link Ok} or not. */
+  isOk(): this is Ok {
+    return false;
+  }
+
+  /** Whether the {@link Result} is {@link Err} or not. */
+  isErr(): this is Err {
+    return true;
+  }
 }
 
 /** Represent {@link Ok} or {@link Err}.  */