|
|
|
# Notes From a Beginning GHC Hacker
|
|
|
|
|
|
|
|
## General notes (some just for Windows)
|
|
|
|
|
|
|
|
1. [The Building Guide](http://www.haskell.org/ghc/docs/latest/html/building/index.html) is very good, read the appropriate parts.
|
|
|
|
1. Optimize your set up for build speed. Having to wait 10 minutes to compile because you added an export to a critical module is no fun.
|
|
|
|
|
|
|
|
1. Use MSYS, not cygwin. MSYS is **much** faster.
|
|
|
|
1. Do not use -O to compile GHC while you are making heavy changes. Once things compile smoothly and you want to test it, compile with optimization (on my machine, adding -O triples the compile time for a fresh 'make').
|
|
|
|
1. If you do a 'make tags' then you can go right to the definition of a function (from any module) using alt-. in emacs.
|
|
|
|
1. If you need to add or delete modules, use 'make boot' to fix up the dependencies.
|
|
|
|
|
|
|
|
## Notes on the type system (and its interactions)
|
|
|
|
|
|
|
|
|
|
|
|
The compiler is, of course, found in the fptools/compiler directory. Important subdirectories for hacking on the type system include:
|
|
|
|
|
|
|
|
- basicTypes (Name, Var, OccName)
|
|
|
|
- prelude (PrelNames, TysWiredIn)
|
|
|
|
- types
|
|
|
|
- typecheck
|
|
|
|
- iface (IfaceType, BinIface)
|
|
|
|
- parser (ParserCore)
|
|
|
|
|
|
|
|
|
|
|
|
The critical parts dealing with types are in the 'types' and 'typecheck' directories:
|
|
|
|
|
|
|
|
**types**
|
|
|
|
|
|
|
|
- TypeRep.lhs
|
|
|
|
|
|
|
|
- The representation of types, the Type datatype, is defined here and exported concretely
|
|
|
|
- A few crucial type constructors (like -\>) are defined here in order to avoid excessive module loops
|
|
|
|
- TyCon.lhs
|
|
|
|
|
|
|
|
- The representation of type constructors, TyCon, is defined here and exported abstractly
|
|
|
|
- Construction and manipulation functions for type constructors are here
|
|
|
|
- Type.lhs
|
|
|
|
|
|
|
|
- Contains the bulk of the type system, imports the concrete representation from TypeRep, and re-exports Type abstractly
|
|
|
|
|
|
|
|
|
|
|
|
(more to come)
|
|
|
|
|
|
|
|
## Debugging the compiler
|
|
|
|
|
|
|
|
1. Make good use of `ASSERT ( booleanCondition )`, or better yet, `ASSERT2 ( booleanCondition, msg )`
|
|
|
|
1. You can add typecheking status messages with `!traceTc sDoc`
|
|
|
|
1. Read about the [GHC Debugging Options](http://www.haskell.org/ghc/docs/latest/html/users_guide/options-debugging.html); the following debugging options are particularly useful:
|
|
|
|
|
|
|
|
- -ddump-tc-trace : shows the typechecking status messages inserted by `traceTc`
|
|
|
|
- -ddump-simpl : shows the Core code after simplification
|
|
|
|
- -dppr-debug : makes the debugging dumps more noisy (and useful); among other things, shows kinds for type variables
|
|
|
|
|
|
|
|
## Running the testsuite
|
|
|
|
|
|
|
|
|
|
|
|
To run the testsuite:
|
|
|
|
|
|
|
|
1. darcs get --partial http://darcs.haskell.org/testsuite
|
|
|
|
1. make the compiler **and** libraries
|
|
|
|
1. cd testsuite/tests/ghc-regress; make |
