Impressions on GHC debugger
Dear all, Yesterday I darcs-got the GHC HEAD to play with the debugger and I have the following impressions/bug/suggestions: * I would like to know whether I am debugging mode (i.e. in a breakpoint) or not. For example
*Main> -- normal prompt
and, for example,
*Main:[1] > -- in breakpoint 1
now, if I evaluate expression "e" via "seq e ()" and it happens to trigger breakpoint 2, I would like to see something like
*Main:[1]:[2] >
or some better notation, but you get my point. * The notation for printing a list is non-Haskell, consider the following evaluated head but unevaluated tail:
*Main> :print xs xs = [True | (_t2::[Bool])]
I would have expected "True : (_t2::[Bool])" * Consider the following code:
mymap f [] = [] mymap f (x:xs) = f x:mymap f xs
main = mapM_ putStrLn $ mymap ('a':) ["hello","bye"]
First, I set a breakpoint on line two. When I invoke "main", the breakpoint is triggered two times before "main" is done evaluating. Afterwards, If I type "main" at the ghci prompt again, the breakpoint is not triggered anymore! Even though ":show breaks" lists it. * Again considering the code above, if I break at line 2:
Stopped at FreeVar2.hs:2:17-19 x :: GHC.Base.Unknown f :: t -> a xs :: [GHC.Base.Unknown]
Now I type "f" and the following message appears:
*** Exception: No match in record selector Var.tcTyVarDetails
* I was wondering whether it would be nice to have a "break" function/ primitive, so that you can write:
mymap f [] = [] mymap f (x:xs) = (break (f x):mymap f xs)
with "break" having type "a -> a" and inserting a breakpoint around the argument expression. It is handy to not have to recalculate lines. However I am not so sure anymore. Using line numbers is not as bad as I thought. The debugger is a nice addition to GHC, and I look forward to the debugger being integrated into the Emacs Haskell mode! Cheers, Alexey
Thanks Alexey. I'm working on ironing out all the wrinkles at the moment. Some of the things you point out, like the prompt, are already on my ToDo list, and some others I didn't know about, but I'll look into them all in due course. Cheers, Simon Alexey Rodriguez Yakushev wrote:
Yesterday I darcs-got the GHC HEAD to play with the debugger and I have the following impressions/bug/suggestions:
* I would like to know whether I am debugging mode (i.e. in a breakpoint) or not. For example
*Main> -- normal prompt
and, for example,
*Main:[1] > -- in breakpoint 1
now, if I evaluate expression "e" via "seq e ()" and it happens to trigger breakpoint 2, I would like to see something like
*Main:[1]:[2] >
or some better notation, but you get my point.
* The notation for printing a list is non-Haskell, consider the following evaluated head but unevaluated tail:
*Main> :print xs xs = [True | (_t2::[Bool])]
I would have expected "True : (_t2::[Bool])"
* Consider the following code:
mymap f [] = [] mymap f (x:xs) = f x:mymap f xs
main = mapM_ putStrLn $ mymap ('a':) ["hello","bye"]
First, I set a breakpoint on line two. When I invoke "main", the breakpoint is triggered two times before "main" is done evaluating. Afterwards, If I type "main" at the ghci prompt again, the breakpoint is not triggered anymore! Even though ":show breaks" lists it.
* Again considering the code above, if I break at line 2:
Stopped at FreeVar2.hs:2:17-19 x :: GHC.Base.Unknown f :: t -> a xs :: [GHC.Base.Unknown]
Now I type "f" and the following message appears:
*** Exception: No match in record selector Var.tcTyVarDetails
* I was wondering whether it would be nice to have a "break" function/primitive, so that you can write:
mymap f [] = [] mymap f (x:xs) = (break (f x):mymap f xs)
with "break" having type "a -> a" and inserting a breakpoint around the argument expression. It is handy to not have to recalculate lines. However I am not so sure anymore. Using line numbers is not as bad as I thought.
The debugger is a nice addition to GHC, and I look forward to the debugger being integrated into the Emacs Haskell mode!
Cheers,
Alexey
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Thanks a lot for the feedback !
On 19/04/2007, at 15:59, Simon Marlow wrote:
> Thanks Alexey. I'm working on ironing out all the wrinkles at the
> moment. Some of the things you point out, like the prompt, are
> already on my ToDo list, and some others I didn't know about, but
> I'll look into them all in due course.
>
> Cheers,
> Simon
>
> Alexey Rodriguez Yakushev wrote:
>> Yesterday I darcs-got the GHC HEAD to play with the debugger and I
>> have the following impressions/bug/suggestions:
>> * I would like to know whether I am debugging mode (i.e. in a
>> breakpoint) or not. For example
>> > *Main> -- normal prompt
>> and, for example,
>> > *Main:[1] > -- in breakpoint 1
>> now, if I evaluate expression "e" via "seq e ()" and it happens to
>> trigger breakpoint 2, I would like to see something like
>> > *Main:[1]:[2] >
>> or some better notation, but you get my point.
>> * The notation for printing a list is non-Haskell, consider the
>> following evaluated head but unevaluated tail:
>> > *Main> :print xs
>> > xs = [True | (_t2::[Bool])]
>> I would have expected "True : (_t2::[Bool])"
I'm working mostly on :print now, while Simon and Bernie work on
breakpoints.
As agreed in #haskell, the pretty printer will be haskellized
promptly, and all Prolog traces will be eliminated :)
>> * Consider the following code:
>> > mymap f [] = []
>> > mymap f (x:xs) = f x:mymap f xs
>> >
>> > main = mapM_ putStrLn $ mymap ('a':) ["hello","bye"]
>> First, I set a breakpoint on line two. When I invoke "main", the
>> breakpoint is triggered two times before "main" is done
>> evaluating. Afterwards, If I type "main" at the ghci prompt again,
>> the breakpoint is not triggered anymore! Even though ":show
>> breaks" lists it.
>> * Again considering the code above, if I break at line 2:
>> > Stopped at FreeVar2.hs:2:17-19
>> > x :: GHC.Base.Unknown
>> > f :: t -> a
>> > xs :: [GHC.Base.Unknown]
>> Now I type "f" and the following message appears:
>> > *** Exception: No match in record selector Var.tcTyVarDetails
In this case the debugger does cannot know what the type of t is.
We still need a good plan for functions. But I totally agree it
shouldn't fail like that.
>> * I was wondering whether it would be nice to have a "break"
>> function/primitive, so that you can write:
>> > mymap f [] = []
>> > mymap f (x:xs) = (break (f x):mymap f xs)
>> with "break" having type "a -> a" and inserting a breakpoint
>> around the argument expression. It is handy to not have to
>> recalculate lines. However I am not so sure anymore. Using line
>> numbers is not as bad as I thought.
>> The debugger is a nice addition to GHC, and I look forward to the
>> debugger being integrated into the Emacs Haskell mode!
Take a look at Shim[1]. The debugger integration will be there soon
(well, sooner or later).
[1] http://shim.haskellco.de
Cheers
pepe
participants (3)
-
Alexey Rodriguez Yakushev -
Pepe Iborra -
Simon Marlow