Question

Hey haskellers and haskellettes,
is it possible to load a module functions in a list.
in my concrete case i have a list of functions all checked with or

checkRules :: [Nucleotide] -> Bool
checkRules nucs = or $ map ($ nucs) [checkRule1, checkRule2]

i do import checkRule1 and checkRule2 from a seperate module – i don’t know if i will need more of them in the future.

i’d like to have the same functionality look something like

-- import all functions from Rules as rules where
-- :t rules ~~> [([Nucleotide] -> Bool)]

checkRules :: [Nucleotide] -> Bool
checkRules nucs = or $ map ($ nucs) rules

the program sorts Pseudo Nucleotide Sequences in viable and nonviable squences according to given rules.
thanks in advance ε/2

---

Addendum:
So do i think right – i need:

genList :: File -> TypeSignature -> [TypeSignature]
chckfun :: (a->b) -> TypeSignature -> Bool

at compile time.
but i can’t generate a list of all functions in the module – as they most probably will have not the same type signature and hence not all fit in one list. so i cannot filter given list with chckfun.

• In order to do this i either want to check the written type signatures in the source file (?) or the inferenced types given by the compiler(?).

• another problem that comes to my mind is: not every function written in the source file might get exported ?

• Is this a problem a haskell beginner should try to solve after 5 months of learning – my brain is shaped like a klein’s bottle after all this “compile time thinking”.

Answer 1

There is a nice package on Hackage just for this: language-haskell-extract. In particular, the Template Haskell function functionExtractor takes a regular expression and returns a list of the matching top level bindings as (name, value) pairs. As long as they all have matching types, you’re good to go.

{-# LANGUAGE TemplateHaskell #-}
import Language.Haskell.Extract

myFoo = "Hello"
myBar = "World"

allMyStuff = $(functionExtractor "^my")

main = print allMyStuff

Output:

[("myFoo", "Hello"), ("myBar", "World")]