Name: Anonymous 2010-01-07 20:36
Seibel: So how do you actually look at it?
Peyton Jones: GHC has flags that let you say, in rather a batch-dumpy kind of way, “Just print out various things.”
Seibel: Built-in print statement debugging?
Peyton Jones: Yes. And it’s aided by the fact that the structure is like most compilers: it has this top-level structure of a pipeline of things that happen.
If something’s gone wrong in the middle of one of these passes, then that could be a bit trickier. But I tend to use rather unsophisticated debugging techniques. Just show me the program before and after this pass. Aaah, I see what’s going wrong. Or sometimes I don’t see what’s going wrong so then I might scatter a few unsafe printfs around to show me what’s actually going on.
There are various debugging environments for Haskell—a summer student, Pepe Iborra, did a nice one earlier this year which now comes with GHC, which is an interactive debugger of some kind. Which I’ve not used very much yet. Partly because we haven’t had one for so long, because it’s less obvious how do you single-step a functional program.
It’s been a kind of interesting research question of how you go about debugging functional programs for some time. It’s a bit embarrassing that we can’t tick that box in a straightforward way, but that makes it an interesting
research problem.
That was the long way around of saying that I tend to use terribly crude debugging techniques with unsafe printfs. And I’m not very proud of that.
But for a long time we didn’t have anything else. At least as far as GHC is concerned, I’ve evolved mechanisms that mean that’s the shortest path to completion for me.
Peyton Jones: GHC has flags that let you say, in rather a batch-dumpy kind of way, “Just print out various things.”
Seibel: Built-in print statement debugging?
Peyton Jones: Yes. And it’s aided by the fact that the structure is like most compilers: it has this top-level structure of a pipeline of things that happen.
If something’s gone wrong in the middle of one of these passes, then that could be a bit trickier. But I tend to use rather unsophisticated debugging techniques. Just show me the program before and after this pass. Aaah, I see what’s going wrong. Or sometimes I don’t see what’s going wrong so then I might scatter a few unsafe printfs around to show me what’s actually going on.
There are various debugging environments for Haskell—a summer student, Pepe Iborra, did a nice one earlier this year which now comes with GHC, which is an interactive debugger of some kind. Which I’ve not used very much yet. Partly because we haven’t had one for so long, because it’s less obvious how do you single-step a functional program.
It’s been a kind of interesting research question of how you go about debugging functional programs for some time. It’s a bit embarrassing that we can’t tick that box in a straightforward way, but that makes it an interesting
research problem.
That was the long way around of saying that I tend to use terribly crude debugging techniques with unsafe printfs. And I’m not very proud of that.
But for a long time we didn’t have anything else. At least as far as GHC is concerned, I’ve evolved mechanisms that mean that’s the shortest path to completion for me.