Re: [Haskell-beginners] Fwd: using Shake to compile c++

David McBride writes:

Sorry this should have been sent to the list.

---------- Forwarded message ---------- From: David McBride Date: Sat, Jul 8, 2017 at 8:49 AM Subject: Re: [Haskell-beginners] using Shake to compile c++ To: Roger Mason

There's three errors here. pkg-config is an IO action and thus in order to use its output, you must use <- instead of a let binding. Then you must choose what you want to save from that command. You could get the exit result, stderr or stdout or both stdout and stderr. We want stdout. And lastly, Stdout is parameterized over a type a, and you have to decide which.

You can either do the following

Stdout i <- cmd "pkg-config glib-2.0 --cflags" () <- cmd "c++ -c" [c] "-o" [out] "-MMD -MF" [m] [i :: String]

Or you can enable ScopedTypeVariables and go Stdout (i :: String) <- cmd "pkg-config glib-2.0 --cflags"

I don't really understand why Stdout is parameterized, rather than just being forced to be a string like Stdin, that's a question for the shake authors.

For the record, I have currently "objects//*.o" %> \out -> do let c = dropDirectory1 $ out -<.> "cxx" let m = out -<.> "m" Stdout i <- cmd "pkg-config glib-2.0 --cflags" need i () <- cmd "c++ -c" [c] "-o" [out] "-MMD -MF" [m] [i :: String] needMakefileDependencies m and get Build.hs:31:59: error: * Couldn't match type `[Char]' with `Char' Expected type: String Actual type: [FilePath] * In the expression: i :: String In the 7th argument of `cmd', namely `[i :: String]' In a stmt of a 'do' block: () <- cmd "c++ -c" [c] "-o" [out] "-MMD -MF" [m] [i :: String] I thank you very much for your help but it is clear that the use of Shake requires rather more Haskell knowledge than is implied by the docs. Given that this is just the easy part of the build the prospects for early success look scant so I will move on and try something else. Thanks again, Roger