Changes between Initial Version and Version 3 of Ticket #7354


Ignore:
Timestamp:
Oct 26, 2012 4:03:55 PM (18 months ago)
Author:
simonpj
Comment:

Right. I can reproduce this failure with 7.6.1. Happily HEAD says:

$ ~/5builds/HEAD/inplace/bin/ghc-stage2 --interactive T7354.hs
GHCi, version 7.7: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling T7354            ( T7354.hs, interpreted )
Ok, modules loaded: T7354.
*T7354> ana alg

<interactive>:2:5:
    Occurs check: cannot construct the infinite type:
      a ~ Base t (Prim [a] a)
    Expected type: Prim [a] a -> Base t (Prim [a] a)
      Actual type: Prim [a] a -> a
    Relevant bindings include
      it :: Prim [a] a -> t (bound at <interactive>:2:1)
    In the first argument of `ana', namely `alg'
    In the expression: ana alg
    In an equation for `it': it = ana alg

which looks right.

Next is to try recursion-schemes with HEAD.

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  • Ticket #7354

    • Property Difficulty changed from to Unknown
  • Ticket #7354 – Description

    initial v3  
    331. Install GHC 7.6.1 and recursion-schemes ([http://hackage.haskell.org/package/recursion-schemes]) 
    442. Create a new .hs file with the following 
    5 -------------- 
     5{{{ 
    66import Data.Functor.Foldable 
    77 
    88foo = embed () 
    9 -------------- 
     9}}} 
    10103. Load the file into GHCI 
    11114. Evaluate foo 
    12  
     12{{{ 
    1313*Main> foo 
    1414 
     
    2626      Use -ddump-if-trace to get an idea of which file caused the error 
    2727    In the expression: foo 
    28  
    29 5. Evaluate ``embed ()'' directly at the REPL 
     28}}} 
     295. Evaluate `embed ()' directly at the REPL 
     30{{{ 
    3031*Main> embed () 
    3132ghc: panic! (the 'impossible' happened) 
     
    3334        nameModule 
    3435<<details unavailable>> 
     36}}} 
    3537 
    36 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug 
    37 -------------- 
    3838 
    3939System Information: 
    40  
     40{{{ 
    4141[andy@vanir ~]$ uname -a 
    4242Linux vanir 3.5.6-1-ARCH #1 SMP PREEMPT Sun Oct 7 19:30:49 CEST 2012 x86_64 GNU/Linux 
    4343[andy@vanir ~]$ ls asdf.hi # the would-be .hi file 
    4444ls: cannot access asdf.hi: No such file or directory 
     45}}}