Schema to Pretty Printer

The Pretty.make function is used to create pretty printers that generate a formatted string representation of values based on a schema.

Example (Pretty Printer for a Struct Schema)

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)@since ― 3.10.0
Struct({
4
  
name: typeof Schema.String
name: 
import Schema
Schema.
class String
export String@since ― 3.10.0
String,
5
  
age: typeof Schema.Number
age: 
import Schema
Schema.
class Number
export Number@since ― 3.10.0
Number
6
})
7

8
// Create a pretty printer for the schema
9
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@since ― 3.10.0
make(
const Person: Schema.Struct<{
    name: typeof Schema.String;
    age: typeof Schema.Number;
}>
Person)
10

11
// Format and print a Person object
12
var console: Console
The 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 and
process.stderr. 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 for
more information.
Example using the global console:
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:
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
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void
Prints 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)
(the arguments are all passed to util.format()).
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() for more information.
@since ― v0.1.100
log(
const PersonPretty: (a: {
    readonly name: string;
    readonly age: number;
}) => string
PersonPretty({ 
name: string
name: "Alice", 
age: number
age: 30 }))
13
/*
14
Output:
15
'{ "name": "Alice", "age": 30 }'
16
*/

Customizing Pretty Printer Generation

You can customize how the pretty printer formats output by using the pretty annotation within your schema definition.

The pretty annotation takes any type parameters provided (typeParameters) and formats the value into a string.

Example (Custom Pretty Printer for Numbers)

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

3
// Define a schema with a custom pretty annotation
4
const 
const schema: Schema.SchemaClass<number, number, never>
schema = 
import Schema
Schema.
class Number
export Number@since ― 3.10.0
Number.
Annotable<SchemaClass<number, number, never>, number, number, never>.annotations(annotations: Schema.Annotations.GenericSchema<number>): Schema.SchemaClass<number, number, never>
Merges a set of new annotations with existing ones, potentially overwriting
any duplicates.
annotations({
5
  
Annotations.GenericSchema<number>.pretty?: (..._: any) => Pretty.Pretty<number>
pretty: (/**typeParameters**/) => (
value: number
value) => `my format: ${
value: number
value}`
6
})
7

8
// Create the pretty printer
9
const 
const customPrettyPrinter: (a: number) => string
customPrettyPrinter = 
import Pretty
Pretty.
const make: <number, number, never>(schema: Schema.Schema<number, number, never>) => (a: number) => string@since ― 3.10.0
make(
const schema: Schema.SchemaClass<number, number, never>
schema)
10

11
// Format and print a value
12
var console: Console
The 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 and
process.stderr. 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 for
more information.
Example using the global console:
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:
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
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void
Prints 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)
(the arguments are all passed to util.format()).
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() for more information.
@since ― v0.1.100
log(
const customPrettyPrinter: (a: number) => string
customPrettyPrinter(1))
13
// Output: "my format: 1"