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diff --git a/compat/README b/compat/README new file mode 100644 index 0000000000..8d0697beb4 --- /dev/null +++ b/compat/README @@ -0,0 +1,32 @@ +GHC compatibiliy library: libghccompat.a +---------------------------------------- + +This library contains interfaces that are available in recent versions +of GHC, but may or may not be available in older versions. The idea +is to provide an abstraction layer and reduce the amount of #ifdefery +and code duplication in GHC and its tools. Furthermore, we can add +modules to the main library and start using them right away in GHC, by +adding a stub to this compat library. + +There are two types of modules in here: + +(a) a module with the same name as a module in the main library + (eg. Distribution.Package). If the module is available in + the main library, then we don't include it in libghccompat. + Otherwise, we have a stub module here that just #includes + the source from the real location under libraries/. Go look + at Distribution/Package.hs for example. + +(b) a module that doesn't exist in another library. For example, + Compat.RawSystem. These modules are used to provide functions + that are available in newer versions of the main libraries. + +BIG NOTE: when building stage 2 of GHC, libghccompat is not used, +because we would have to build another version of it. Instead, we +just use the appropriate libraries directly. For (a)-type modules, +just import the module directly. For (b)-type modules, a single +#ifdef will be required to choose between the Compat version and +the real version. + +In stage 1 of GHC, and tools (eg. ghc-pkg, runghc), libghccompat.a +is linked in, so all its libraries will be accessible. |