Traditionally, GF_LIB_PATH points to something like
`.../share/ghc-8.0.2-x86_64/gf-3.9/lib`
and if you want prelude and alltenses and present, you add a
`--# -path=.:present`
compiler pragma to the top of your .gf file
But if you are developing some kind of application grammar
library or contrib of your own, you might find yourself
repeating your library path at the top of all your .gf files.
After painstakingly maintaining the same library path at the
top of all your .gf files, you might say, let's factor this
out into GF_LIB_PATH.
Then you might then find to your surprise that GF_LIB_PATH
doesn't accept the usual colon:separated:path notation
familiar from, say, unix PATH and MANPATH.
This patch allows you to define
`GF_LIB_PATH=gf-3.9.lib:$HOME/gf-contrib/whatever/lib`
in a more natural way.
If you are an RGL hacker and have your own version of the
RGL tree sitting somewhere, you should be able to have both
paths in the GF_LIB_PATH, for added convenience. This minor
convenience will probably lead to obscure bugs and great
frustration when you find that your changes are mysteriously
not being picked up by GF; so keep this in mind and use it
cautiously.
This caution should probably sit in the documentation
somewhere. A subsequent commit will do that.
If you use zsh, you can do this to quickly build up a big
GF_LIB_PATH:
% gf_lib_path=( $HOME/src/GF/lib/src/{api,abstract,common,english,api/libraryBrowser,prelude,..} )
% typeset -xT GF_LIB_PATH gf_lib_path
* In GHC 8.4.1, the operator <> has become a method of the Semigroup class
and is exported from the Prelude. This is unfortunate, since <> is also
exported from the standard library module Text.PrettyPrint, so in any
module that defines a pretty printer, there is likely to be an ambiguity.
This affects ~18 modules in GF. Solution:
import Prelude hiding (<>)
This works also in older versions of GHC, since GHC does't complain if
you hide something that doesn't exists.
* In GHC 8.4.1, Semigroup has become a superclass of Monoid. This means
that anywhere you define an instance of the Monoid class you also have to
define an instance in the Semigroup class.
This affects Data.Binary.Builder in GF. Solution: conditionally define
a Semigroup instance if compiling with base>=4.11 (ghc>=8.4.1)
