#3560: Template Haskell attempts to load unnecessary packages
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Reporter: heatsink | Owner:
Type: bug | Status: new
Priority: normal | Component: Template Haskell
Version: 6.10.4 | Severity: normal
Keywords: | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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To run TH splices, GHC's interpreter loads all packages specified on the
command line, even if they are not needed. This causes compilation to
fail when an unused package works with the compiler, but not with the
interpreter.
Consider the one-line program {{{{-# LANGUAGE TemplateHaskell #-} main =
print $([|1|])}}}. I can compile it with {{{ghc --make Main.hs}}}. If I
add the extra command line parameter {{{-package WeakTest}}}, compilation
fails when attempting to load the WeakTest package. (This package
demonstrates a GHCi bug and is attached to #3333).
Why put a superfluous package on the command line? This may happen
because a build system uses the same set of flags to compile every file.
This is the current behavior of Cabal.
A possible solution would be for GHC to reuse the mechanism that GHC
--make uses for deciding which command line packages to actually load.
This way, extra packages won't prevent compilation. This would make it
easier to use TH in a project that relies on non-interpreted packages.
See also #3333. Possibly related #2555.
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3560>
GHC <http://www.haskell.org/ghc/>
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