[Copying Tim and Ian Lynagh who might be interested.]
| I noticed that Template Haskell support is included only in | Stage 2 builds and that it depends on the availability of | non-"base" libraries (in particular, "haskell-src"). Both true. | This | seems to imply that Template Haskell features can neither be | used inside GHC (in the same way, as eg RULES are used to | simplify some optimisations inside GHC, such as constructor | specialisation) You mean, can you use TH stuff in the GHC source code? Yes, of course you can. You just need to compile that source code with at least a stage-2 compiler. Aha. That means that we'd need to change the bootstrap process though. At the moment we 1 Compile STAGE-1 with existing GHC (call it EXISTING) 2 Compile STAGE-2 with STAGE-1 3 Compile STAGE-3 with STAGE-2 But if you use TH in the GHC source code, step 2 won't work. Instead we'd have to 1 Compile STAGE-1 with EXISTING 2 Compile STAGE-2 with EXISTING ...aha... I see what you mean. This won't work either. The point of the restriction to a stage2 compiler for GHCi and TH is this. Consider a data structure built by running code compiled by stage2 (e.g. as a result of running a top-level splice). This data structure will be taken apart by the stage2 compiler itself, which was compiled by stage1. So that's fine, because stage1 and stage2 are going to agree on the layout of data structures, because they are the same compiler. But EXISTING might have a different data structure layout. So there must be a stage in which a compiler X, compiled by EXISTING, is compiling GHC. There is no guarantee that X and EXISTING share data structure layouts, so it follows that GHC can't require TH extensions. Interesting point! You go on to say: | and worse TH stuff can't be used inside the standard | libraries (unless we want to introduce a third stage). Can't be used in the 'base' package, but *only* base is needed to compile GHC I think, so you can use TH in other packages (incl parallel arrays). Just don't compile those libraries in STAGE1. Simon _______________________________________________ Cvs-ghc mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/cvs-ghc
