December 2016 - Glasgow-haskell-users

Stack traces in ghci
by Dominic Steinitz 08 Dec '16

08 Dec '16

I am trying to debug a package in which there is a divide by 0 error and attempting to use Simon Marlow’s stack traces: https://simonmar.github.io/posts/2016-02-12-Stack-traces-in-GHCi.html. However ghci is complaining about missing symbols. What do I need to add to the command line to coax ghci into giving me a stack trace? > ~/Dropbox/Private/Stochastic/demo $ ghci -fexternal-interpreter -prof fe-handling-example.o -i../../monad-bayes/src -package-db=.cabal-sandbox/x86_64-osx-ghc-8.0.1-packages.conf.d > GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help > Prelude> :l app/Main.hs > [ 1 of 16] Compiling Control.Monad.Bayes.LogDomain ( ../../monad-bayes/src/Control/Monad/Bayes/LogDomain.hs, interpreted ) > [ 2 of 16] Compiling Control.Monad.Bayes.Primitive ( ../../monad-bayes/src/Control/Monad/Bayes/Primitive.hs, interpreted ) > [ 3 of 16] Compiling Control.Monad.Bayes.Class ( ../../monad-bayes/src/Control/Monad/Bayes/Class.hs, interpreted ) > [ 4 of 16] Compiling Control.Monad.Bayes.Sampler ( ../../monad-bayes/src/Control/Monad/Bayes/Sampler.hs, interpreted ) > [ 5 of 16] Compiling Control.Monad.Bayes.Sequential ( ../../monad-bayes/src/Control/Monad/Bayes/Sequential.hs, interpreted ) > [ 6 of 16] Compiling Control.Monad.Bayes.Prior ( ../../monad-bayes/src/Control/Monad/Bayes/Prior.hs, interpreted ) > [ 7 of 16] Compiling Control.Monad.Bayes.Rejection ( ../../monad-bayes/src/Control/Monad/Bayes/Rejection.hs, interpreted ) > [ 8 of 16] Compiling Control.Monad.Bayes.Weighted ( ../../monad-bayes/src/Control/Monad/Bayes/Weighted.hs, interpreted ) > [ 9 of 16] Compiling Control.Monad.Bayes.Population ( ../../monad-bayes/src/Control/Monad/Bayes/Population.hs, interpreted ) > [10 of 16] Compiling Control.Monad.Bayes.Deterministic ( ../../monad-bayes/src/Control/Monad/Bayes/Deterministic.hs, interpreted ) > [11 of 16] Compiling Control.Monad.Bayes.Conditional ( ../../monad-bayes/src/Control/Monad/Bayes/Conditional.hs, interpreted ) > [12 of 16] Compiling Control.Monad.Bayes.Dist ( ../../monad-bayes/src/Control/Monad/Bayes/Dist.hs, interpreted ) > [13 of 16] Compiling Control.Monad.Bayes.Coprimitive ( ../../monad-bayes/src/Control/Monad/Bayes/Coprimitive.hs, interpreted ) > [14 of 16] Compiling Control.Monad.Bayes.Trace ( ../../monad-bayes/src/Control/Monad/Bayes/Trace.hs, interpreted ) > [15 of 16] Compiling Control.Monad.Bayes.Inference ( ../../monad-bayes/src/Control/Monad/Bayes/Inference.hs, interpreted ) > [16 of 16] Compiling Main ( app/Main.hs, interpreted ) > > app/Main.hs:92:7: warning: [-Wunused-matches] > Defined but not used: ‘a’ > > app/Main.hs:92:9: warning: [-Wunused-matches] > Defined but not used: ‘prevP’ > > app/Main.hs:92:15: warning: [-Wunused-matches] > Defined but not used: ‘prevZ’ > > app/Main.hs:106:5: warning: [-Wunused-do-bind] > A do-notation statement discarded a result of type ‘GHC.Prim.Any’ > Suppress this warning by saying > ‘_ <- ($) > error (++) "You are here " (++) show state (++) " " show p_obs’ > Ok, modules loaded: Main, Control.Monad.Bayes.LogDomain, Control.Monad.Bayes.Primitive, Control.Monad.Bayes.Class, Control.Monad.Bayes.Population, Control.Monad.Bayes.Conditional, Control.Monad.Bayes.Inference, Control.Monad.Bayes.Sampler, Control.Monad.Bayes.Rejection, Control.Monad.Bayes.Weighted, Control.Monad.Bayes.Sequential, Control.Monad.Bayes.Trace, Control.Monad.Bayes.Dist, Control.Monad.Bayes.Prior, Control.Monad.Bayes.Deterministic, Control.Monad.Bayes.Coprimitive. > *Main> main > ghc-iserv-prof: > lookupSymbol failed in relocateSection (relocate external) > /Users/dom/Dropbox/Private/Stochastic/demo/.cabal-sandbox/lib/x86_64-osx-ghc-8.0.1/hmatrix-0.18.0.0-7aYEqJARQEvKYNyM4UGAPZ/libHShmatrix-0.18.0.0-7aYEqJARQEvKYNyM4UGAPZ_p.a: unknown symbol `___ieee_divdc3' > ghc-iserv-prof: Could not on-demand load symbol '_vectorScan' > > ghc-iserv-prof: > lookupSymbol failed in relocateSection (relocate external) > /Users/dom/Dropbox/Private/Stochastic/demo/.cabal-sandbox/lib/x86_64-osx-ghc-8.0.1/hmatrix-0.18.0.0-7aYEqJARQEvKYNyM4UGAPZ/libHShmatrix-0.18.0.0-7aYEqJARQEvKYNyM4UGAPZ_p.a: unknown symbol `_vectorScan' > ghc-iserv-prof: Could not on-demand load symbol '_hmatrixzm0zi18zi0zi0zm7aYEqJARQEvKYNyM4UGAPZZ_InternalziVectorizzed_constantAux_closure' > > ghc-iserv-prof: > lookupSymbol failed in relocateSection (relocate external) > /Users/dom/Dropbox/Private/Stochastic/demo/.cabal-sandbox/lib/x86_64-osx-ghc-8.0.1/hmatrix-0.18.0.0-7aYEqJARQEvKYNyM4UGAPZ/libHShmatrix-0.18.0.0-7aYEqJARQEvKYNyM4UGAPZ_p.a: unknown symbol `_hmatrixzm0zi18zi0zi0zm7aYEqJARQEvKYNyM4UGAPZZ_InternalziVectorizzed_constantAux_closure' > ghc-iserv-prof: Could not on-demand load symbol '_hmatrixzm0zi18zi0zi0zm7aYEqJARQEvKYNyM4UGAPZZ_InternalziMatrix_Matrix_con_info' > > ghc-iserv-prof: > lookupSymbol failed in relocateSection (relocate external) > /Users/dom/Dropbox/Private/Stochastic/demo/.cabal-sandbox/lib/x86_64-osx-ghc-8.0.1/hmatrix-0.18.0.0-7aYEqJARQEvKYNyM4UGAPZ/libHShmatrix-0.18.0.0-7aYEqJARQEvKYNyM4UGAPZ_p.a: unknown symbol `_hmatrixzm0zi18zi0zi0zm7aYEqJARQEvKYNyM4UGAPZZ_InternalziMatrix_Matrix_con_info' > ghc-iserv-prof: Could not on-demand load symbol '_hmatrixzm0zi18zi0zi0zm7aYEqJARQEvKYNyM4UGAPZZ_InternalziElement_zgzl_info' > > ghc-iserv-prof: > lookupSymbol failed in relocateSection (relocate external) > /Users/dom/Dropbox/Private/Stochastic/demo/.cabal-sandbox/lib/x86_64-osx-ghc-8.0.1/hmatrix-0.18.0.0-7aYEqJARQEvKYNyM4UGAPZ/libHShmatrix-0.18.0.0-7aYEqJARQEvKYNyM4UGAPZ_p.a: unknown symbol `_hmatrixzm0zi18zi0zi0zm7aYEqJARQEvKYNyM4UGAPZZ_InternalziElement_zgzl_info' > ghc-iserv-prof: Could not on-demand load symbol '_hmatrixzm0zi18zi0zi0zm7aYEqJARQEvKYNyM4UGAPZZ_InternalziUtil_zdfIndexableVectorDouble_closure' > > > ByteCodeLink.lookupCE > During interactive linking, GHCi couldn't find the following symbol: > hmatrixzm0zi18zi0zi0zm7aYEqJARQEvKYNyM4UGAPZZ_InternalziUtil_zdfIndexableVectorDouble_closure > This may be due to you not asking GHCi to load extra object files, > archives or DLLs needed by your current session. Restart GHCi, specifying > the missing library using the -L/path/to/object/dir and -lmissinglibname > flags, or simply by naming the relevant files on the GHCi command line. > Alternatively, this link failure might indicate a bug in GHCi. > If you suspect the latter, please send a bug report to: > glasgow-haskell-bugs(a)haskell.org Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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Floating Point Exceptions
by Dominic Steinitz 07 Dec '16

07 Dec '16

Hello again, I removed my dependency on hmatrix and enabled floating point exceptions via `feenableexcept` hoping to get a call stack showing me where the exception was being raised but alas all I get is > *Main> main > ghc: ghc-iserv terminated (-8) > Leaving GHCi. My googling didn’t turn up much but as far as I can tell ghc does *not* handle sigfpe (googling "haskell sigfpe” turns up blog posts on Haskell by someone called “sigfpe”). I think it would be jolly useful to be able to get stack traces of floating point exceptions. How much work would this be? I’d be happy to have a go at it if someone could provide help and guidance. There seems to have been some discussion of it on the ghc-devs mailing list in September (https://mail.haskell.org/pipermail/ghc-devs/2016-September/date.html) but not much in the way of write up. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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"instrumenting" functions
by Ranjit Jhala 01 Dec '16

01 Dec '16

Hi all, Given a module with top-level (functions) f1 ... fn, I would like to generate/compile an "instrumented" version where, say, each function prints the string "hello", every time it is called. Can anyone suggest some ways of doing this? One option is a core-to-core transform with an unsafePerformIO (print "hello") stuck into the appropriate places. But perhaps there are better ways? Ideally I'd like to instrument each "App" to log every function application. Are other libraries or tools that use the GHC API to do this sort of thing? Thanks in advance! Ranjit.

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