enum_type.md

EnumType

To create an enum instance using the EnumType constructor

const Type = EnumType([ 'SubType1', 'SubType2', 'SubType3' ]);

const Maybe = EnumType({
    Just: [ 'value' ],
    Nothing: [],
});

You can also specify and document the arguments for the constructor using enum-fp/types

import Enum, { T } from 'enum-fp';

const CanvasObject = EnumType({
    Point: [ T.Number('x'), T.Number('y') ], // Fixed types
    Circle: [ 'radius', 'x', 'y' ], // Dynamic types
    Text: [ T.String() ],
    Clear: [], // 0 arguments. For dynamic number of arguments, use null
});

API

• Constructor

EnumType :: Object Array | Array String -> EnumType

• #{SubType}

const point = Canvas.Point(20, 25);
const circle = Canvas.Circle(20, 50, 50);
const clearScreen = Canvas.Clear();

• #match

Pattern matching for the sub-types

match :: (SubType, Object ((...*) -> b)) ~> b

const circle = Canvas.Circle(20, 50, 50);

const result = Canvas.match(circle, {
    Circle: (radius, x, y) => drawCircle(radius, x, y),
    Point: (x, y) => drawPoint(x, y),
    Clear: () => clearCanvasScreen(),
});
// `result` is the result of the matched operation

• #cata

An alternate api for match. The arguments are flipped and curried for a nice, point-free experience.

cata :: Object ((...*) -> b) ~> SubType -> b

const draw = Canvas.cata({
    Circle: (radius, x, y) => drawCircle(radius, x, y),
    Point: (x, y) => drawPoint(x, y),
    Clear: () => clearCanvasScreen(),
});

draw(Canvas.Clear());
draw(Canvas.Circle(20, 50, 50));
draw(Canvas.Point(20, 25));

• #caseOf

Alias for cata. Same api as cata.

caseOf :: Object ((...*) -> b) ~> SubType -> b

const draw = Canvas.caseOf({
    Circle: (radius, x, y) => drawCircle(radius, x, y),
    Point: (x, y) => drawPoint(x, y),
    Clear: () => clearCanvasScreen(),
});

draw(Canvas.Clear());
draw(Canvas.Circle(20, 50, 50));
draw(Canvas.Point(20, 25));

• #reduce Alias for cata. Same api as cata.

reduce :: Object ((...*) -> b) ~> SubType -> b

const draw = Canvas.reduce({
    Circle: (radius, x, y) => drawCircle(radius, x, y),
    Point: (x, y) => drawPoint(x, y),
    Clear: () => clearCanvasScreen(),
});

draw(Canvas.Clear());
draw(Canvas.Circle(20, 50, 50));
draw(Canvas.Point(20, 25));

#### Explanation of sum-types

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