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)