algesten/plift-pseq.md

## plift-pseq.md

      
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              plift-pseq.md
            
          
    Implemented in https://github.com/algesten/fnuc/blob/master/src/fnuc.coffee#L202
Case for plift

This example shows how plift can help to treat functions dealing with promises as regular functions.
N.B. This code is a "handler" it is not intended to be side effect free.

userToDevices is a function looking up devices from a user id in a database. It returns a promise for the result.
ex.publish publishes the result over AMQP. Our wrapper makes this also return a promise.

However, when writing the test code for these functions, we can simply ignore that there are any promises involved. Both ex and userToDevices can be mocked to return immediate function returns and we can still be confident it works for promises.
{firstfn, map, mixin, plift, sequence} = require 'fnuc'
Q = require 'q'

ppipe = (fs...) -> sequence (map(plift) fs)...  # sequence of plifted funcs

# mixin the message into the device specification
deviceWithMessage = (message) -> (d) -> mixin d, {message}

# check if given array has any promise
anyPromise = firstfn Q.isPromiseAlike

# wait for all promises in array to resolve or just return array
waitFor = (todo) -> if anyPromise(todo) then Q.all(todo) else todo

# {user:<userid>, message:{title:<title>, body:<body>}}
module.exports = (ex, userToDevices) ->

    # publish the message to exchange
    publish = (m) -> ex.publish 'device', m

    (user, message) ->
        ppipe(
            userToDevices,
            map(deviceWithMessage(message)),
            map(publish),
            waitFor
        ) user