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{ a, b }:
with import <nixpkgs> {};

let
  runHaskell = name: deps: code: pkgs.runCommand name { buildInputs = [ (pkgs.haskellPackages.ghcWithPackages deps) ]; } ''
    runhaskell ${pkgs.writeText "${name}.hs" code}
  '';
in runHaskell "do-da-math" (ps: []) ''
  {-# LANGUAGE OverloadedStrings #-}
  module Main (main) where

  import qualified Data.ByteString as BS
  import qualified Data.ByteString.Char8 as BSC
  import System.Environment

  main :: IO ()
  main = do
    let
      a :: Integer
      a = ${a}
      b :: Integer
      b = ${b}
    output <- getEnv "out"
    BS.writeFile output (BSC.pack $ show (a * b))
''

[clever@amd-nixos:~]$ nix-build math.nix --argstr a 4294967296 --argstr b 4294967296
these derivations will be built:
  /nix/store/dbjigm9n6nia5cmfbv9cnlnm240z78sy-do-da-math.hs.drv
  /nix/store/1yq4lh0wwy563jp8d7awii030makjxy8-do-da-math.drv
building path(s) ‘/nix/store/ph39dp1ffckjidhjyhgj4p1685vw8d4a-do-da-math.hs’
building path(s) ‘/nix/store/ab8m9ar1bg5p3h8bs2v8x5lk35mwjnmg-do-da-math’
/nix/store/ab8m9ar1bg5p3h8bs2v8x5lk35mwjnmg-do-da-math

[clever@amd-nixos:~]$ cat result
18446744073709551616