How to dynamically call a function which defined in multiple modules in the same signature

Question

I've defined a lot of functions (say, 100+), each of which do a specific work but with the same signature. That is something like:

module R001 (run) where run = <do-...>
module R002 (run) where run = <do-...>

What I wanna do is to provide the actual 'run' as user input, such that:

main = do
         runWith $ read $ getLine
       where
         runWith :: Int -> IO ()
         runWith n = R<n-padded-with-0>.run

Currently, I import all modules qualified, and put all the run's into a list of [Maybe (IO())], so this works:

runWith n = case Rs !! (read $ getLine) of 
              Just run -> run
              Nothing -> undefined

But as the n grows, I have to continously maintain a big list.

Is there any way I can define the big list using TemplateHaskell, or just load the corresponding module as needed at runtime without having to seperate each module into different shared libraries.

---

Based on epsilonhalbe's answer, I did some research:

import R1 (run1)
import R2 (run2)

test = $(functionExtractor "^run")

main :: IO ()
main = do
         putStrLn $ show $ length $ test
         run1 -- remove on second attempt
         run2 -- remove on second attempt

This block of code prints 2 following the results of run1 and run2. If I remove the last two lines, it just prints 0. It seems that functions imported but not referenced won't be extracted ...

Answer 1

I once had a similar problem haskell load module in list maybe this helps.

You can create a list of functions with regexp and choose a function by userinput from that list. I don't know if you have to import all "runs" qualified by hand or if you can

import R*.hs (run)

i would rather write one file with run1 = …, run2 = … and generate a list of all runs and a function chooser function which takes a function from a list of functions with the same type signature.

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

main = do
     let listOfRuns = $(functionExtractor "^run")
     putStrLn "please choose a run"
     putStrLn $ show listOfRuns
     let run = runWith $ read $ getLine
     run
   where
     runWith n = listOfRuns !! n

Attention: I have not run this code this is just a stream of thought put in haskell syntax

i hope this is helpful

---

After edit:
In my example i wrote all run* in one file and there i generated the list of all run functions, which worked instantly - have a look at my Nucleotide Project especially the files Rules.hs and Nucleotide.hs.

Runs.hs

module Runs where
import Language.Haskell.Extract

listOfRuns = map snd $(functionExtractor "^run")

run1 = …
run2 = …

Main.hs

import Runs

main = do
     putStrLn "please choose a run"
     putStrLn $ show listOfRuns
     let run = runWith $ read $ getLine
     run
  where
    runWith n = listOfRuns !! n

happy to be helpful

Answer 2

Is it absolutely critical that the different run functions live in different modules? If you can put them all in one module, you could make run be a function of an Int (or Integer if you prefer).

module AllMyCircuits where
run 0 = {- do blah blah blah -}
run 1 = {- do blah blah blah -}
run 2 = {- do yikes -}

module Main where
import AllMyCircuits
main = readLn >>= run