!import "base" !Local
!import "list" !Local
!import "io"   !Local

-- Transform an IO result.
--   mapIO applies a pure function to the value produced by an action.
--   Run with --allow-read PATH or --unsafe-io.

safeRead = (path :
  bind (readFile path)
    (result :
      matchResult
        (err rest : pure "missing")
        (contents rest : pure contents)
        result))

shout = (path :
  mapIO (safeRead path)
    (text : append text "!!!"))

main = io (bind 
    (shout "demos/interactionTrees/greet.tri")
    (text : putStrLn text))