GHCi debugger status

Daniil Elovkov daniil.elovkov at
Fri Nov 21 05:23:43 EST 2008

Hello folks

I'd like to know, how do ghc developers and users feel about the debugger?

I'm using it to some extent on ghc 6.8.2 and find it useful. But I'm getting an impression that it's not too stable. I'm not filing any bug report yet, just want to know how it feels for others.

I used to make it panic. I think, it was due to existential types.

Now I see it mess up the list of bindings in a funny way. For example, in a previous trace session I had a variable, say, prev. It was bound during pattern matching in a function, say, prevFunc. Now I'm having another trace session, actually stepping from the very beginning. A couple of steps after the beginning, prev suddenly appears in the bindings where prevFunc absolutely has not yet been invoked. It's completely unrelated. In 'show bindings' prev has a wrong type - SomeType (it's ADT). Its real type (when in scope) is [t]. I ask 'length prev' and get 0 :)

So, what is your impression of the debugger?

Daniil Elovkov

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