[Haskell-beginners] using Shake to compile c++

[David McBride]

The easy option is to just use command instead of cmd.  Variadic
functions are always a little weird to type check.

command_ [] "pkg-config" ["glib-2.0","--cflags"]

That will *probably* solve the ambiguity in both lines, but I haven't tested.

On Sat, Jul 8, 2017 at 7:19 AM, Roger Mason <rmason at mun.ca> wrote:
> Hello,
>
> I am trying the Shake build system to compile some c++.  I would
> appreciate some advice on how to use the result of a call to pkg-config
> in constructing a compiler command.  This is what I have currently in Build.hs:
>
> import Development.Shake
> import Development.Shake.Command
> import Development.Shake.FilePath
> import Development.Shake.Util
>
> main :: IO ()
> main = shakeArgs shakeOptions{shakeFiles="bin"} $ do
>     want ["bin/makelist", "bin/makejpeg" <.> exe]
>
>     phony "clean" $ do
>         putNormal "Cleaning files in _build"
>         removeFilesAfter "bin" ["//*"]
>
>     "bin/makelist" <.> exe %> \out -> do
>         cs <- getDirectoryFiles "" ["src/MakeList.cxx"]
>         let os = ["objects" </> c -<.> "o" | c <- cs]
>         need os
>         cmd "c++ -o" [out] os
>
>     "bin/makejpeg" <.> exe %> \out -> do
>         cs <- getDirectoryFiles "" ["src/MakeJpeg.cxx"]
>         let os = ["objects" </> c -<.> "o" | c <- cs]
>         need os
>         cmd "c++ -o" [out] os
>
>     "objects//*.o" %> \out -> do
>         let c = dropDirectory1 $ out -<.> "cxx"
>         let m = out -<.> "m"
>         let i = cmd "pkg-config glib-2.0 --cflags"
>         () <- cmd "c++ -c" [c] "-o" [out] "-MMD -MF" [m] [i]
>         needMakefileDependencies m
>
> This is the output from 'stack runhaskell Build.sh':
>
> Build.hs:29:17: error:
>     * Ambiguous type variable `t0' arising from a use of `cmd'
>       prevents the constraint `(CmdArguments t0)' from being solved.
>       Relevant bindings include i :: t0 (bound at Build.hs:29:13)
>       Probable fix: use a type annotation to specify what `t0' should be.
>       These potential instances exist:
>         instance CmdResult r => CmdArguments (IO r)
>           -- Defined in `Development.Shake.Command'
>         instance CmdResult r => CmdArguments (Action r)
>           -- Defined in `Development.Shake.Command'
>         instance (Development.Shake.Command.Arg a, CmdArguments r) =>
>                  CmdArguments (a -> r)
>           -- Defined in `Development.Shake.Command'
>         ...plus one other
>         (use -fprint-potential-instances to see them all)
>     * In the expression: cmd "pkg-config glib-2.0 --cflags"
>       In an equation for `i': i = cmd "pkg-config glib-2.0 --cflags"
>       In the expression:
>         do { let c = dropDirectory1 $ out -<.> "cxx";
>              let m = out -<.> "m";
>              let i = cmd "pkg-config glib-2.0 --cflags";
>              () <- cmd "c++ -c" [c] "-o" [out] "-MMD -MF" [m] [i];
>              .... }
>
> Build.hs:30:15: error:
>     * Ambiguous type variable `t0' arising from a use of `cmd'
>       prevents the constraint `(Development.Shake.Command.Arg
>                                   [t0])' from being solved.
>       Relevant bindings include i :: t0 (bound at Build.hs:29:13)
>       Probable fix: use a type annotation to specify what `t0' should be.
>       These potential instances exist:
>         instance Development.Shake.Command.Arg [CmdOption]
>           -- Defined in `Development.Shake.Command'
>         instance Development.Shake.Command.Arg [String]
>           -- Defined in `Development.Shake.Command'
>         instance Development.Shake.Command.Arg String
>           -- Defined in `Development.Shake.Command'
>     * In a stmt of a 'do' block:
>         () <- cmd "c++ -c" [c] "-o" [out] "-MMD -MF" [m] [i]
>       In the expression:
>         do { let c = dropDirectory1 $ out -<.> "cxx";
>              let m = out -<.> "m";
>              let i = cmd "pkg-config glib-2.0 --cflags";
>              () <- cmd "c++ -c" [c] "-o" [out] "-MMD -MF" [m] [i];
>              .... }
>       In the second argument of `(%>)', namely
>         `\ out
>            -> do { let ...;
>                    let ...;
>                    .... }'
>
> I would appreciate any help in getting the output of the call to
> pkg-config into the compiler invocation.
>
> Thanks,
> Roger
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