[clean-list] True Uniqueness Typing Error or Compiler Bug ?

[Fabien Todescato]

Dear Cleaners,

I get the following uniqueness typing error from the 2.0.2 compiler :

Type error [uTypeBug.icl,14,nextSymbol] : specified type

  ( Char -> Int -> u:File -> u:File) (u:File->u:File) Int u:File -> u:File

conflicts with derived type 

  ( Char -> Int -> * File -> * File) (* File->* File) Int * File -> * File

which I find quite confusing since the former type can be unified with the
latter with the substitution u = '*'.

This arises when trying to compile the following code snippet :


module uTypeBug

import StdEnv

class
  nextSymbol context thread symbol
  :: ( symbol context .thread -> .thread )
     ( .thread -> .thread )
     context .thread -> .thread

instance
  nextSymbol Int File Char
where
  nextSymbol yes no index file
  # (ok,file) = fseek file index FSeekSet
  | not ok = no file
  # (ok,char,file) = freadc file
  | not ok = no file
  # index = index + 1
  = yes char index file

Start = "uTypeBug"


Any clue ?

Best regards, Fabien Todescato

PS.Happy new year to you all, and kudos to the Clean Team for bringing to us
a lot of improvement to an already great system.