This is the error message which started it all off: http://lpaste.net/104242 Then the following conversation happened: ============================================================================== --- JPMoresmau ------ First package to fail is exceptions. Just open a console and type in cabal install exceptions EclipseFP tries to put some parallel install flags that may make the errors less visible (a Cabal thing, not an EclipseFP thing). I really don't like the look of getting warnings in c code, though... --- haskell_beginner ------ $ cabal install exceptions Resolving dependencies... Configuring exceptions-0.6.1... /var/folders/3r/gvk584k50jb253024p4wxy3r0000gn/T/5187.c:1:12: warning: control reaches end of non-void function [-Wreturn-type] int foo() {} ^ 1 warning generated. Building exceptions-0.6.1... Preprocessing library exceptions-0.6.1... <command line>: cannot satisfy -package-id mtl-2.1.2-94c72af955e94b8d7b2f359dadd0cb62 (use -v for more information) Failed to install exceptions-0.6.1 cabal: Error: some packages failed to install: exceptions-0.6.1 failed during the building phase. The exception was: ExitFailure 1 $ What flags can I add to that to get a better error message? EDIT TO ADD: Again if there is another layer automatically adding flags to the above command, I know nothing about it. This includes if Haskell or cabal uses a config file. I am on a — to my knowledge — completely stock install of Haskell for Mac OS. --- JPMoresmau ------ cabal install -v exceptions May give more info about why the mtl package cannot be satisfied when it seems to have been installed. --- haskell_beginner ------ $ cabal install -v exceptions Reading available packages... Choosing modular solver. Resolving dependencies... Ready to install exceptions-0.6.1 Waiting for install task to finish... Extracting /Users/person/Library/Haskell/repo-cache/ hackage.haskell.org/exceptions/0.6.1/exceptions-0.6.1.tar.gz to /var/folders/3r/gvk584k50jb253024p4wxy3r0000gn/T/exceptions-0.6.1-5256... Updating exceptions.cabal with the latest revision from the index. Configuring exceptions-0.6.1... Dependency base ==4.6.0.1: using base-4.6.0.1 Dependency mtl ==2.1.2: using mtl-2.1.2 Dependency transformers ==0.3.0.0: using transformers-0.3.0.0 /var/folders/3r/gvk584k50jb253024p4wxy3r0000gn/T/5256.c:1:12: warning: control reaches end of non-void function [-Wreturn-type] int foo() {} ^ 1 warning generated. Using Cabal-1.16.0 compiled by ghc-7.6 Using compiler: ghc-7.6.3 Using install prefix: /Users/person/Library/Haskell/ghc-7.6.3/lib/exceptions-0.6.1 Binaries installed in: /Users/person/Library/Haskell/ghc-7.6.3/lib/exceptions-0.6.1/bin Libraries installed in: /Users/person/Library/Haskell/ghc-7.6.3/lib/exceptions-0.6.1/lib Private binaries installed in: /Users/person/Library/Haskell/ghc-7.6.3/lib/exceptions-0.6.1/libexec Data files installed in: /Users/person/Library/Haskell/ghc-7.6.3/lib/exceptions-0.6.1/share Documentation installed in: /Users/person/Library/Haskell/ghc-7.6.3/lib/exceptions-0.6.1/doc Using alex version 3.0.5 found on system at: /usr/bin/alex Using ar found on system at: /usr/bin/ar No c2hs found Using cpphs version 1.18.1 found on system at: /Users/person/Library/Haskell/bin/cpphs No ffihugs found Using gcc version 4.2.1 found on system at: /usr/bin/gcc Using ghc version 7.6.3 found on system at: /usr/bin/ghc Using ghc-pkg version 7.6.3 found on system at: /usr/bin/ghc-pkg No greencard found Using haddock version 2.13.2 found on system at: /usr/bin/haddock Using happy version 1.18.10 found on system at: /usr/bin/happy No hmake found Using hpc version 0.6 found on system at: /usr/bin/hpc Using hsc2hs version 0.67 found on system at: /usr/bin/hsc2hs Using hscolour version 1.20 found on system at: /Users/person/Library/Haskell/bin/HsColour No hugs found No jhc found Using ld found on system at: /usr/bin/ld No lhc found No lhc-pkg found No nhc98 found No pkg-config found Using ranlib found on system at: /usr/bin/ranlib Using strip found on system at: /usr/bin/strip Using tar found on system at: /usr/bin/tar No uhc found creating dist/build creating dist/build/autogen Building exceptions-0.6.1... Preprocessing library exceptions-0.6.1... Building library... creating dist/build /usr/bin/ghc --make -fbuilding-cabal-package -O -odir dist/build -hidir dist/build -stubdir dist/build -i -idist/build -isrc -idist/build/autogen -Idist/build/autogen -Idist/build -optP-include -optPdist/build/autogen/cabal_macros.h -package-name exceptions-0.6.1 -hide-all-packages -package-db dist/package.conf.inplace -package-id base-4.6.0.1-6c351d70a24d3e96f315cba68f3acf57 -package-id mtl-2.1.2-94c72af955e94b8d7b2f359dadd0cb62 -package-id transformers-0.3.0.0-ff2bb6ac67241ebb987351a3db564af0 -XHaskell98 Control.Monad.Catch Control.Monad.Catch.Pure -Wall -fwarn-tabs -O2 <command line>: cannot satisfy -package-id mtl-2.1.2-94c72af955e94b8d7b2f359dadd0cb62 (use -v for more information) Failed to install exceptions-0.6.1 World file is already up to date. cabal: Error: some packages failed to install: exceptions-0.6.1 failed during the building phase. The exception was: ExitFailure 1 $ Hope that helps. I don't know what to make of it. :-/ --- JPMoresmau ------ Neither do I! It seems cabal finds a mtl package to use, but when it passes the exact reference of the package (with a trailing hash to indicate the specifics of your install), ghc doesn't find it. At least it's nothing to do with EclipseFP, which is a relief (for me :-p). I suggest you post that to the Haskell-Cafe mailing list if nobody has any clue here. I know that MacOS is a bit weird sometimes with PATH and such. ============================================================================== Thus with the history of this error now told (TL;DR: read JPMoresmau's last comment above), the question I pose to this mailing list is: Why is ghc failing to find mtl? Thanks, ~Haskell Beginner