Int-based lexer flag bitmask exhausted

Simon Peyton Jones simonpj at
Mon Jun 23 10:00:06 UTC 2014

I'm all for it. Just need to watch for performance regressions


| -----Original Message-----
| From: Herbert Valerio Riedel [mailto:hvriedel at]
| Sent: 21 June 2014 11:10
| To: Simon Peyton Jones
| Cc: ghc-devs
| Subject: Int-based lexer flag bitmask exhausted
| Hello Simon (et al.),
| While doing #9224[1] as a finger-exercise to extend the lexer to support
| base-2 integer literals, I got stuck on the lexer extension map being
| represented as an 'Int', which (in GHC) is only guaranteed to hold least
| 32bits.
| -- for reasons of efficiency, flags indicating language extensions (eg,
| -- -fglasgow-exts or -XParallelArrays) are represented by a bitmap
| -- stored in an unboxed Int
| However, as all 32bits are already taken up by language extensions, and
| I'd need a 33th bit, I'm wondering how to proceed. Can we replace the
| 'Int' by an 'Int64' (or even better a Word64, ideally with a newtype or
| at least a type-synonym around it?) which would give us a bit more
| headroom while being semantically sound even for 'bitSize Int == 32'?
|  [1]:
| Cheers,
|    hvr

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