haskell-debug parse error

[dschrempf]

Hello,

I tried to debug qsort with haskell-debug (cf. ghci debugger). When I try to step through qsort.hs I get a parse error after about 5 to 10 steps:

Debugger entered--Lisp error: (error "Unable to parse history entry: -1  : qsort:(...) (/home/dominik/Dropbox/programming/haskell/myqsort.hs:3:24-56)")
  signal(error ("Unable to parse history entry: -1  : qsort:(...) (/home/dominik/Dropbox/programming/haskell/myqsort.hs:3:24-56)"))
  error("Unable to parse history entry: %s" "-1  : qsort:(...) (/home/dominik/Dropbox/programming/haskell/myqsort.hs:3:24-56)")
  haskell-debug-parse-history-entry("-1  : qsort:(...) (/home/dominik/Dropbox/programming/haskell/myqsort.hs:3:24-56)")
  mapcar(haskell-debug-parse-history-entry ("-1  : qsort:(...) (/home/dominik/Dropbox/programming/haskell/myqsort.hs:3:24-56)" "-2  : qsort (/home/dominik/Dropbox/programming/haskell/myqsort.hs:(1,1)-(3,56))" "-3  : qsort (/home/dominik/Dropbox/programming/haskell/myqsort.hs:2:16-25)" "-4  : qsort (/home/dominik/Dropbox/programming/haskell/myqsort.hs:2:16-47)" "-5  : qsort (/home/dominik/Dropbox/programming/haskell/myqsort.hs:(1,1)-(3,56))" "-6  : main (/home/dominik/Dropbox/programming/haskell/myqsort.hs:5:15-47)" "-7  : main (/home/dominik/Dropbox/programming/haskell/myqsort.hs:5:8-48)"))
  haskell-debug-get-history()
  haskell-debug/refresh()
  haskell-debug-start(((name . "haskell") (next-error-region #<marker at 1 in *haskell*> . #<marker (moves after insertion) at 362 in *haskell*>) (next-error-locus) (interactive-buffer . #<buffer *haskell*>) (current-dir . "/home/dominik/Dropbox/programming/haskell/") (cabal-checksum) (cabal-dir . "/home/dominik/Dropbox/programming/haskell/") (process (name . "haskell") (current-response-cursor . 0) (current-response . "") (command-queue) (inferior-process . #<process haskell>) (is-restarting) (current-command) (suggested-imported) (sent-stdin) (evaluating) (session (name . "haskell") (next-error-region #<marker at 1 in *haskell*> . #<marker (moves after insertion) at 362 in *haskell*>) (next-error-locus) (interactive-buffer . #<buffer *haskell*>) (current-dir . "/home/dominik/Dropbox/programming/haskell/") (cabal-checksum) (cabal-dir . "/home/dominik/Dropbox/programming/haskell/") #1))))
  haskell-debug()
  call-interactively(haskell-debug record nil)
  command-execute(haskell-debug record)
  execute-extended-command(nil "haskell-debug")
  call-interactively(execute-extended-command nil nil)
  command-execute(execute-extended-command)

The file qsort.hs:

qsort [] = []
qsort (a:as) = qsort left ++ [a] ++ qsort right
  where (left,right) = (filter (<=a) as, filter (>a) as)

main = print (qsort [8, 4, 0, 3, 1, 23, 11, 18])

Best,
Dominik

[gracjan]

I tried to reproduce this, but failed.
@fazky : can you tell your version of GHCi, GHC, and just copy and paste what your session looks like?

[chrisdone]

For what it's worth after implementing this and using GHCi some, I've found the ghci debugger to be drastically useless. Setting a breakpoint almost always results in a no-op which GHCi simply ignores. It's a pity because the mode I made is nice. But it's a real stab in the dark whether GHCi underneath will behave in a predictable manner, otherwise I'd be using this all the time.

[gracjan]

True and sad.
Lets wait till end of Feb 2015 so that @fazky can provide more info. If not close this as 'cannot reproduce'.

[dschrempf]

Hello,

the error is still there; maybe I got something wrong in my configuration. I can reproduce it with:

1. Open myqsort.hs (given above) in haskell-mode.
2. Start interpreter: C-c C-z y RET RET
3. Load myqsort.hs in interpreter: :l myqsort.hs.
4. Switch back to the myqsort.hs buffer and open M-x haskell-debug.
5. Insert a breakpoint at function main with hotkey b.
6. Step into expression main with hotkey s.
7. At the 8th step the error happens.

My ghci session (version 7.8.4):

The lambdas must flow.
If I break, you can:
  1. Restart:           M-x haskell-process-restart
  2. Configure logging: C-h v haskell-process-log (useful for debugging)
  3. General config:    M-x customize-mode
  4. Hide these tips:   C-h v haskell-process-show-debug-tips
Changed directory: /home/dominik/Dropbox/programming/haskell/
λ> :l myqsort.hs
[1 of 1] Compiling Main             ( myqsort.hs, interpreted )
Ok, modules loaded: Main.
λ> 

My haskell-debug session one step before the error happens:

Debugging haskell

s - step into an expression, b - breakpoint
d - delete breakpoint, a - abandon context, c - continue
p - previous step, n - next step
g - refresh

Context

main - myqsort.hs (stopped)

(filter (<=a) as, filter (>a) as)

_result :: ([Integer], [Integer]) = _
a :: Integer = 8
as :: [Integer] = [4,0,3,1,23,....]

   6 qsort [] = [] qsort (a:as) = qsort left ++ [a] ++ qsort right where (left,right) = (filter (<=a) as, filter (>a) as)
   5 qsort left
   4 qsort left ++ [a] ++ qsort right
   3 qsort [] = [] qsort (a:as) = qsort left ++ [a] ++ qsort right where (left,right) = (filter (<=a) as, filter (>a) as)
   2 qsort [8, 4, 0, 3, 1, 23, 11, 18]
   1 print (qsort [8, 4, 0, 3, 1, 23, 11, 18])

breakpoints

0 - Main (5:8)

Modules

Main - myqsort.hs

I hope this helps,
Dominik

Edit: I use haskell-mode from MELPA version 20150108.346

[gracjan]

Thanks, that should help to reproduce the problem!

[abbradar]

I have probably somewhat related bug -- haskell-debug cannot parse operator <|> (maybe others, haven't studied it better). I can provide more info if it can't be reproduced. I have haskell-mode-20150331.1140.

[gracjan]

Closing as old. If somebody would like to take case of haskell-debug.el then we can talk again.