@jadesrochers/functionalmonads

Functionalmonads

An experiment in integrating monads with functional programming constructs.
Just to make it simple to add them into pipe/flow if you want.

Whats the Use?

To be able to use monads in the same way as fp in ramda/lodash
without needing to get into the implementation details each time.

installation

npm install @jadesrochers/functionalmonads
const fm = require('@jadesrochers/functionalmonads')

Usage

Four monads available: Maybe, Either, Ask, Reader There are some sub versions of these, and async/await support as well.

Use the Maybe monad to shortcircuit pipes -

You can pass a monad or a raw value, which will be converted
into a monad.
If the pipe encounters a value that changes the monad to None,
igores the rest of the functions.

Setup some test functions to use

const fm = require('@jadesrochers/functionalmonads')  
let retzero = n => 0
let retblank = n => ''
let retfalse = n => false
let retund = n => undefined
let retnull = n => null

let testfn1 = n => n+1
let testfn2 = n => n+2
let testprom1 = n => Promise.resolve(n+1)
let testprom2 = n => Promise.resolve(n+2)

pipeMayNull pipes functions using a maybe monad for null values

If there is a null, then the Monad gets switched to None
and no further functions in the pipe are used.

let maytest = fm.pipeMayNull(
   retzero,
   retblank,
   testfn2,
)(3)
let maytest2 = fm.pipeMayNull(
   testfn1,
   retnull,
   testfn2,
)(3)

maytest.some()
// 2
maytest2.some()
// Error, because it is a None
maytest2.isSome()
// false

pipeMayUnd pipes functions using a maybe monad for undefined values

If there is a null, then the Monad gets switched to None
and no further functions in the pipe are used.

let undtest = fm.pipeMayUnd(
     retblank,
     retfalse,
     testfn2,
 )(3)
let undtest2 = fm.pipeMayUnd(
   testfn1,
   retund,
   testfn2,
 )(3)

undtest.some()
// 2
undtest2.isSome()
// The second test is none because a fcn returned undefined

pipeMayfalsy pipes functions using a maybe monad for falsy values

If there is a falsy value (false, blank, empty, 0), then the Monad gets switched to None
and no further functions in the pipe are used.

let falsetest = fm.pipeMayFalsy(
   retzero,
   testfn1,
)(3)
let falsetest2 = fm.pipeMayFalsy(
   retfalse,
   testfn1,
)(3)
let falsetest3 = fm.pipeMayFalsy(
   retblank,
   testfn1,
)(3)

// All are false
falsetest.isSome()
falsetest2.isSome()
falsetest3.isSome()

Async version of Reader, Maybe

Unlike the Mayfalsy/und/null these do not lift and flatten so
the input determines some/none.
Reader is just for run later abilities.

var redtestAsync = fm.pipeAsyncReader(
   testprom1,
   testprom2,
)(0)
redtestAsync.run().then(n => console.log(n))
// 3

var maytestAsync = fm.pipeAsyncMaybe(
   testprom1,
   testprom2,
)(0)
maytestAsync.isSome()
maytestAsync.some().then(n => console.log(n))
// true, 3

pipeReader to use a reader monad in pipe

The Reader attaches funtions, but runs only when .run() is called.
It allows the setup to be run later.

let redtest = fm.pipeReader(
   testfn1,
   testfn2,
)(0)

redtest.run()
// 3

pipeEither to use a either monad in pipe

The Reader attaches funtions, but runs only when .run() is called.

const M = require('monet')
var eithtest = fm.pipeEither(
   testfn1,
   testfn2,
)(M.Either.left(0))
var eithtest2 = fm.pipeEither(
   testfn1,
   testfn2,
)(0)
eithtest.left()
// 0, because the left was ignored
eithtest2.right()
// 3

pipeAsk allows dependency injection via ask monad

Pass values at runtime to functions at various places in pipes.
Makes use of Reader.ask.

Define function that needs the injected value (second arg)

let testAsk1 = a => b => a + b

When calling them, use fm.chainAsk to inject the value
fm.chainAsk(n => testAsk1(n)),

// Define a sub-pipe that needs the injected value
var asktest = fm.pipeAsk(
   testfn1,
   fm.chainAsk(n => testAsk1(n)),
)
// Must add this to make sure the monad gets passed down.
asktest.needMonad = true

// Function calling the nested pipe, and use fm.chainAsk to allow the injection
var asktest2 = fm.pipeAsk(
   testfn1,
   fm.chainAsk(n => testAsk1(n)),
   asktest,
)(0)
// )(M.Reader.of(0))
asktest2.run(1)
// passes value 1 to testAsk1 in both locations
// 4 

pipeAsyncAsk

Same as above, but suppoers async functions

let testPromAsk1 = a => b => Promise.resolve(a + b)

Has its own helper to pass the value -
fm.chainPromAsk(n => testPromAsk1(n)),

var asktest = fm.pipeAsyncAsk(
   testprom1,
   fm.chainPromAsk(n => testPromAsk1(n)),
)
asktest.needMonad = true

var asktest2 = fm.pipeAsyncAsk(
   testprom1,
   fm.chainPromAsk(n => testPromAsk1(n)),
   asktest,
)(0)
asktest2.run(1).then(n => console.log(n))
// 4