Hello Neil (cc Yhc), I am trying to run your catch on the HughesPJ prettyprinter. The serious reason for trying this is that I suspect that some parts of the HughesPJ module are actually never used. That is, certain definitions are impossible to reach using the exported definitions. And I guess (but I haven't progressed far enough to tell) that catch can be used for this, simply by modifying some definition that you suspect is never used to head [] or perhaps just error "Something" and then see if catch can find a case where this error is reported. Another reason is, of course, the expected entertainment value of such an experiment. In the latter, I was not disappointed, as I will now describe in some detail: 1. Catch (http://www.cs.york.ac.uk/fp/darcs/catch/catch.htm) requires me to use Yhc, so I decided to upgrade my Yhc installation. That didn't work out particularly well, as reported separately to yhc@haskell.org. But as a workaround, I am simply using the Yhc that gets built by the Yhc buildbot slave on my machine regularly. For some reason, this still works, even if I am unable to build an entirely fresh Yhc. 2. Trying the catch Risers example, I got this reaction:

$ catch Risers

Executing: /Users/thorkilnaur/tn/install/catch-0.1/share/catch-0.1/examples/Regress/Risers.hs

Compiling yhc: Could not parse cmd-line options: unrecognized option `-l'

catch: Failed to compile, /Users/thorkilnaur/tn/install/catch-0.1/share/catch-0.1/examples/Regress/Risers.hs $

To correct this:

src/Prepare/Compile.hs: res <- system $ "yhc --hide --linkcore \"" ++ file ++ "\" " ++ flags

(This is the http://hackage.haskell.org/packages/archive/catch/0.1.1/catch-0.1.1.tar.gz package that you recommend using). In addition:

Task: Overlay yhc: Could not parse cmd-line options: unrecognized option `-o'

unrecognized option `-r'

unrecognized option `-e'

catch: Failed to compile the overlay

was fixed by:

src/Prepare/Overlay.hs: res <- system $ "yhc --hide --core \"" ++ prim ++ "\""

3. Next on the agenda, we get

$ catch HughesPJ Executing: HughesPJ.hs Compiling Compiling Text.PrettyPrint.HughesPJ ( HughesPJ.hs ) -- during after type inference/checking Error: Type error type clash between Prelude.Int and Prelude.Bool when trying to apply function at 931:26 to its 2nd argument at 931:31-931:33.

catch: Failed to compile, HughesPJ.hs $

This is fixed by changing HughesPJ.hs as follows:

931c931 < lay1 k _ sl _ | k+sl `seq` False = undefined ---

...

lay1 k _ sl _ | (k+sl) `seq` False = undefined

$ catch HughesPJ Executing: HughesPJ.hs Compiling Compiling Text.PrettyPrint.HughesPJ ( HughesPJ.hs ) Loading Core for YHC.Internal ... Loading Core for PreludeAux Linking... catch: ycr/HughesPJ.yca: openBinaryFile: does not exist (No such file or

And this is, of course, rather interesting, since this type error (I cannot see it as anything else) is neither detected by Hugs nor GHC. But that is a matter for further work some other time. 4. Then I get this problem: directory)

$

I have earlier disagreed with yhc as to where it's output files were placed and I also reported a bug about this some time back. This seems to be related, although I must admit that I have not at the time of writing investigated further. The first part of this problem is that bare "yhc HughesPJ" seems to place its output .hi and .hbc files in "../../Text/PrettyPrint/" and this is, of course, somewhat OK if you are already in "$SOMEWHERE/Text/PrettyPrint/". But if you are not, I assure you that this is confusing. So, instead of working with "$SOMEWHERE/HughesPJ.hs", I created "$SOMEWHERE/Text/PrettyPrint/HughesPJ.hs" and started working from there. And thus, I was able to compile with "yhc HughesPJ" and find the output .hi and .hbc files in the same directory as HughesPJ.hs. However, catch HughesPJ still couldn't find its ycr/HughesPJ.yca file. Looking around again, I found the yhc output, as directed by catch, in "$SOMEWHERE/ycr/Text.PrettyPrint.HughesPJ.yca", etc. So because HughesPJ.hs has a module name Text.PrettyPrint.HughesPJ, the --hide option of yhc performs this massaging of the directory and output file name. And, apparently, catch is not able to match yhc in this. This was fixed by changing HughesPJ.hs as follows:

170c170 < module Text.PrettyPrint.HughesPJ ( ---

...

module HughesPJ (

5. And then catch starts to run. It is presently here:

$ catch HughesPJ Executing: HughesPJ.hs Compiling Compiling HughesPJ ( HughesPJ.hs ) Loading Core for YHC.Internal ... Loading Core for PreludeAux Linking... Transformations Task: Overlay Task: Firstify Warning: Failed in stage Firstify Task: LetElim Task: OneArg Task: UniqueVars Task: ShortCtors Analysing Checking [1/19]: Data.Ratio.% with zero as the second argument, bad person Partial: "Data.Ratio.%$142" Answer: _ Checking [2/19]: HughesPJ: Pattern match failure in function at 799:5-804:51. Partial: "HughesPJ.HughesPJ.Prelude.580.get" Partial: "HughesPJ.best"

and it's been there for about an hour, working. But I am sure that you have also noticed the ominous "Warning: Failed in stage Firstify" which may indicate that there is very little chance of getting a useful result anyway. So I will probably just interrupt it before long. I know you are probably busy with other things, so understand that this matter is not particularly critical for me. But if you have any comments to this situation, I would gladly hear about them. Thanks and best regards Thorkil