Flag to get information about the compiler and RTS

[igloo]

There should be a flag +RTS -foo that prints info including:

• The version of GHC used to compile the program
• The sort of RTS linked against
• What (canonicalised) platform it was built for, i.e., powerpc-apple-darwin8.10.0

There should also be a flag that can be given to the compiler that prints info including:

• Whether it has a NCG
• Whether or not it is registerised
• Whether it supports ghci/ghc -e
• What RTSs it has
• Whether it supports SMP

Ideally this would all be easily machine-parseable.

[dons]

• Whether it supports SMP

and how many cpus are available.

Very useful for working out what values of +RTS -Nn, and then what value of 'n' to use to fork the ideal number of threads.

[igloo]

I think "number of CPUs available" would be better in System.Info or similar.

[Isaac Dupree]

Well, "number of CPUs available" should have IO in its type, because there are systems where the number of CPUs can change while they're running. I am already suspicious about the rest of the things in System.Info not having IO types (especially if we consider the potential of portable interpreters similar to Yhc, where a running Haskell program could be moved from one system to another - or even be running concurrently on multiple machines at once (actually, then adding even IO to the types wouldn't make them fully make sense)).

[guest]

standard comments why getArgs has IO in its type is "because it may change from run to run". also, it's easy to use usafePerformIO if we need them in non-IO environment

[p_tanski]

machine-parseable: would one-liner's do? For example: compiled_with: ghc-6.4.1 platform: i386-unknown-mingw32 rts_ways: t, p (use build system codes) registerised: YES (or 1) supports_NCG: YES (or 1) supports_SMP: YES (or 1)

The idea is that all this can go directly from compiler/Makefile into Config.hs into the options. Doesn't need to be after +RTS; might be an argument to ghc --version (no arg means as before; arg with parameter you want returns value like sysctl -n var on Darwin).

[igloo]

I've (locally) fixed the first half.

[igloo]

This is mostly done, but there are a few more bits it would be nice to add to the output

[igloo]

Now done.