GHC/Redesign

This page is a draft.

Goals:

• Separate the GHC specific logic from the library.
• Make better use of the type-system! A lot of GHC is written as if Haskell were dynamically typed.
• Cut down on global mutable variables.

Global mutable variables

SysTools.v_FilesToClean of type [String].

List of temporary files to remove. May contain wildcards [used by DriverPipeline.run_phase SplitMangle].

The other global mutable variables have to do with the linker, initDynFlags, ways and static flags.

Compilation interface

Current interface:

data LoadHowMuch
   = LoadAllTargets
   | LoadUpTo Module
   | LoadDependenciesOf Module
-- 'hscTarget' and 'ghcMode' governs the exact behaviour.
load :: Session -> LoadHowMuch -> IO SuccessFlag

However, there're many invalid combinations of 'hscTarget' and 'ghcMode'.

hscTarget \ ghcMode	Batch	OneShot	Interactive
Hard code (C,asm,etc)	+	+	-
Byte code	-	-	+
Nothing (type-check)	+	-	-

For example, if you set 'ghcMode' to Interactive without changing 'hscTarget' from its 'HscC' default, ghc will try to run 'gcc' on a non-existing file. I'd like to describe the behaviour of 'load' via function composition instead of mutable flags. Moreover, I'd like to remove the targets, module graph and interactive context from the HscEnv.

Alternative interface (pretty much just random ideas for now):

data HscTarget
   = HscC
   | HscAsm
   | HscJava
   | HscILX

compileToBytecode :: Session -> ModSummary -> IO SuccessFlag
compileToHardcode :: Session -> ModSummary -> HscTarget -> IO SuccessFlag
compileToNothing  :: Session -> ModSummary -> IO SuccessFlag

-- unload stable linkables, compile the files, don't link.
batchBytecode :: Session -> [Target] -> IO (SuccessFlag, [ModSummary])

-- compile the files, link.
batchHardcode :: Session -> [Target] -> HscTarget -> IO (SuccessFlag, [ModSummary])

-- typecheck and return CheckedModule's for the given targets.
batchTypecheck :: Session -> [Target] -> IO (SuccessFlag, [CheckedModule])

oneshotHardcode :: Session -> Target -> HscTarget -> IO (SuccessFlag, [ModSummary])
load :: Session - [Target] -> (ModSummary -> IO (Maybe

Clean up of temporary files

GHC is currently using a very ugly 'DriverPipeline.getOutputFilename' function for deciding the output file for a given phase. This is done while we're compiling instead of before, and is causing complications throughout the module. If we separate the file preprocessing (cpp) from the driver pipeline, we can get a complete view of all the output files before we write them. This allows us to abstract the file handling out of the inner pipeline loop.