system-f / exitcode Goto Github PK

Anything that uses the ExitcodeT constructor should test that Left 0 never occurs.

TODO

• make _ExitSuccess more polymorphic 7454505
• Replicate System.Process module, with these differences
  • Write classy lenses for CreateProcess.
  • Write classy prisms for StdStream.
  • Write classy prisms for CmdSpec.
  • Export data types but not fields or functions.
  • Rewrite fields and functions with the same name, but:
    • polymorphic (i.e. use the classy lens) and using better ExitCode structure.
    • Use MaybeT instead of IO (Maybe X).

Since Left 0 is an invalid state, the ExitcodeT constructor needs to be hidden. This can be achieved with an expicit export list in the module.

Let's turn off Prelude and use Papa. This will require getting builds set up, etc.

• MonadReader
• MonadWriter
• MonadState
• MonadRWS
• MonadError
• MonadFix (would result in partial function)
• MonadFail (lacks a sensible instance because Either - see MonadFail proposal
• MonadCont
• Foldable1 (impossible due to Either)
• Traversable1 (impossible due to Either)
• MonadTrans
• MonadZip (would fail information preservation law)
• Eq1
• Ord1
• Show1