haskell - state prepared at app startup and read from without parameters -

i'm finishing little gui app in haskell , right adding translations support. on linux it's easy, can use hgettext, , provides me with

gettext :: string -> io string 

and in fact authors even recommend use so:

__ :: string -> string __ = unsafeperformio . gettext 

it doesn't shock me, after texts displayed screen, it's side-effects, , don't change during runtime of application. without unsafeperformio think it's ok although never needed far in haskell.

however problem can't gettext work on windows , decided roll own system windows. should pretty easy moderate needs. want parse po files , make myself map string string , can have function translations. @ startup find out current language , read translation files... have pass map string string on place in program. every dialog , every little function that'll ask user whether he's sure delete item , on... wrapping entire program in reader monad absolutely overkill think.

i reading memoization, on top-level mutable state, solutions seem overkill. generate hashes @ build-time pretty serious template haskell magic sounds wrong...

i wouldn't shocked global state function sort of ioref (maybe should be...) i'm not sure how code it...

any clues on in particular case?

it's pretty common use standard idiom top-level mutable state:

translations :: ioref (map string string) {-# noinline translations #-} translations = unsafeperformio (newioref map.empty) 

the noinline pragma important make sure doesn't duplicated inlining.

in case type signature doesn't matter much, in other cases it's needed make sure it's monomorphic, otherwise duplicated @ each use site anyway.

you'd need make sure initialise useful data before might read it.

ideally make map string string without ioref , call unsafeperformio (read_translations ...) in definition, depend on whether parameters needed available @ point.