Node.Thunk is a library for PureScript which helps to interface with asynchronous Node.js code:

This simple example shows how to use Node.Thunk to wrap a part of Node.js's fs module:

import Node.Thunk

foreign import fs "var fs = require('fs');" :: {
  readFile :: ThunkFn1 String String
}

readFile = runThunkFn1 fs.readFile

The type ThunkFn1 a b means that a function takes a single argument of type a and produces a result of type b. To convert ThunkFn1 a b into a PureScript function a -> Thunk b we need to apply runThunkFn1 function.

Similarly to ThunkFn1 there exists ThunkFn2, ThunkFn3 for each arity up to 5.

This simple examples shows how to combine computations with thunks:

readFileAndWait = do
  contents <- readFile "./README.md"
  delay 1000
  return contents

delay is a computation which results into Unit value (nothing) after some milliseconds elapsed.

To execute computation you should use runThunk function:

main = runThunk readFileAndWait handle
    where
  handle (Left err) = -- handle error
  handle (Right result) = -- handle result

runThunk function thunk as first argument and handler as second argument. Handler is supplied with either an error or a result.

There's a function liftEff which can lift Eff action into Thunk:

readFileAndPrintContents = do
  contents <- readFile "./README.md"
  liftEff (print contents)