module haskell
imports libstrategolib signatures/- util

signature
  constructors
    TopLevel: Ex -> Ex

rules
  /* Approach: Generate code from the bottom up.
     At every node, we create a pair of the implementation and
     necessary preamble of IO actions.
     We concatenate preambles as we go up.
     Finally, at the toplevel we emit the preamble before returning the
     final value.
   */

  hs: TopLevel((c,p)) -> $[import System.IO
  data IOStream = StdIO

  stdio :: IO IOStream
  stdio = return StdIO

  receives :: Show b => IO a -> b -> IO a
  receives s d = do
    temp <- s
    putStr(show d)
    return temp

  main = do
    [p]return [c]]

  hs: Stdio() -> ("stdio", "")
  hs: Int(x) -> (x, "")
  hs: Sum((c,p)) -> ($[sum [c]], p)
  hs: Receives((c, p), (d, s)) -> ($[[c] `receives` [d]], <conc-strings>(p,s))
  hs: Enters((c, p), (d, s)) -> <hsenter>(c,d,<conc-strings>(p,s),<newname>"fos")

  hsenter: (x, s, p, v) -> (v, <concat-strings>[$[[p]let [v] = [x]], "\n",
                               $[[s] `receives` [v]], "\n"])

  hslist: x -> (<map(Fst); join(|", "); brack>x, <map(Snd); concat-strings>x)
  brack: x -> $<[<x>]>

strategies
  // wrap expression in a toplevel and then apply code generation
  haskell = !TopLevel(<id>); bottomup(try(hs <+ hslist))

  // Interface haskell code generation with editor services and file system
  to-haskell: (selected, _, _, path, project-path) -> (filename, result)
    with filename := <guarantee-extension(|"hs")> path
       ; result   := <haskell> selected