module haskell
imports libstrategolib signatures/-

signature
  constructors
    TopLevel: Ex -> Ex

rules
  hs: TopLevel(x) -> $[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
    [<hs>x]]

  hs: Stdio() -> $[stdio]
  hs: Int(x) -> x
  hs: Sum(x) -> $[sum [<hs>x]]
  hs: Receives(x, y) -> $[[<hs>x] `receives` [<hs>y]]
  hs: [] -> $<[]>
  hs: [x | xs] -> $<[<<hs>x><<hstail>xs>]>

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

  // translate each element of a list, prepending each with ',', and concatenate
  hstail = foldr(!"", \ (x,y) -> $<, <<hs>x><y>> \)

  // 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