Effect Schema to Pretty Printer

Generating Pretty Printers

The Pretty.make function is designed for creating pretty printers that output a formatted string representation of values according to a given schema.

Example

1
import { import Pretty
Pretty, import Schema
Schema } from "effect"
2

3
const const Person: Schema.Struct<{
    name: typeof Schema.String;
    age: typeof Schema.Number;
}>
Person = import Schema
Schema.function Struct<{
    name: typeof Schema.String;
    age: typeof Schema.Number;
}>(fields: {
    name: typeof Schema.String;
    age: typeof Schema.Number;
}): Schema.Struct<{
    name: typeof Schema.String;
    age: typeof Schema.Number;
}> (+1 overload)
namespace Struct
Struct({
4
  (property) name: typeof Schema.String
name: import Schema
Schema.(alias) class String
export String
String,
5
  (property) age: typeof Schema.Number
age: import Schema
Schema.(alias) class Number
export Number
Number
6
})
7

8
const const PersonPretty: (a: {
    readonly name: string;
    readonly age: number;
}) => string
PersonPretty = import Pretty
Pretty.const make: <{
    readonly name: string;
    readonly age: number;
}, {
    readonly name: string;
    readonly age: number;
}, never>(schema: Schema.Schema<{
    readonly name: string;
    readonly age: number;
}, {
    readonly name: string;
    readonly age: number;
}, never>) => (a: {
    readonly name: string;
    readonly age: number;
}) => string
make(const Person: Schema.Struct<{
    name: typeof Schema.String;
    age: typeof Schema.Number;
}>
Person)
9

10
// returns a string representation of the object
11
namespace console
var console: ConsoleThe `console` module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.

The module exports two specific components:

* A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream.
* A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and
[`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module.

_**Warning**_: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for
more information.

Example using the global `console`:

```js
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
```

Example using the `Console` class:

```js
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
```
console.(method) Console.log(message?: any, ...optionalParams: any[]): voidPrints to `stdout` with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html)
(the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)).

```js
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
```

See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.
log(const PersonPretty: (a: {
    readonly name: string;
    readonly age: number;
}) => string
PersonPretty({ (property) name: string
name: "Alice", (property) age: number
age: 30 }))
12
/*
13
Output:
14
'{ "name": "Alice", "age": 30 }'
15
*/

Customizing Pretty Printer Generation

You can tailor the output of the pretty printer by using the pretty annotation within your schema definitions.

Example

1
import { import Pretty
Pretty, import Schema
Schema } from "effect"
2

3
const const schema: Schema.SchemaClass<number, number, never>
schema = import Schema
Schema.(alias) class Number
export Number
Number.(method) Annotable<SchemaClass<number, number, never>, number, number, never>.annotations(annotations: Schema.Annotations.Schema<number, readonly []>): Schema.SchemaClass<number, number, never>Merges a set of new annotations with existing ones, potentially overwriting
any duplicates.
annotations({
4
  (property) Annotations.Schema<number, readonly []>.pretty?: Pretty.PrettyAnnotation<number, readonly []>
pretty: (/**typeParameters**/) => ((parameter) value: number
value) => `my format: ${(parameter) value: number
value}`
5
})
6

7
namespace console
var console: ConsoleThe `console` module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.

The module exports two specific components:

* A `Console` class with methods such as `console.log()`, `console.error()` and `console.warn()` that can be used to write to any Node.js stream.
* A global `console` instance configured to write to [`process.stdout`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstdout) and
[`process.stderr`](https://nodejs.org/docs/latest-v22.x/api/process.html#processstderr). The global `console` can be used without importing the `node:console` module.

_**Warning**_: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the [`note on process I/O`](https://nodejs.org/docs/latest-v22.x/api/process.html#a-note-on-process-io) for
more information.

Example using the global `console`:

```js
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
```

Example using the `Console` class:

```js
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
```
console.(method) Console.log(message?: any, ...optionalParams: any[]): voidPrints to `stdout` with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to [`printf(3)`](http://man7.org/linux/man-pages/man3/printf.3.html)
(the arguments are all passed to [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args)).

```js
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
```

See [`util.format()`](https://nodejs.org/docs/latest-v22.x/api/util.html#utilformatformat-args) for more information.
log(import Pretty
Pretty.const make: <number, number, never>(schema: Schema.Schema<number, number, never>) => (a: number) => string
make(const schema: Schema.SchemaClass<number, number, never>
schema)(1)) // my format: 1

In this setup, the pretty annotation takes any type parameters provided (typeParameters) and formats the value into a string.