once

memoization for IO actions and functions https://gitlab.com/kaction/haskell-once

GPL-3.0-only licensed by Dmitry Bogatov

Maintained by KAction@debian.org

This version can be pinned in stack with:once-0.4@sha256:ce30b72cd90f6eb729f3ad77ac3daf8117d60b6be961b511b46ae1ce4872519c,2463

Package provides single polymorphic function once, that allows you to memoize IO actions and functions, evaluating them at most once.

let mkStamp = (putStrLn "stamping" >> writeFile "/tmp/stamp" "") :: IO ()

-- onceStamp :: IO ()

onceStamp <- once mkStamp

-- onceStamp actually evaluates mkStamp it wraps first time.

onceStamp

stamping

-- but second time result `()' is memoized, no action is performed.

onceStamp

-- we can memoize functions too

foo <- once $ \x -> print "foo" >> print (x :: Int)

-- action will be performed once for every distinct argument

foo 10

foo

foo 10

foo 4

foo

Depends on 5 packages(full list with versions):