#15646: ghci takes super long time to find the type of large fractional number -------------------------------------+------------------------------------- Reporter: Johannkokos | Owner: | JulianLeviston Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: GHCi | Version: 8.4.3 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj):
Why not do the parsing in compile time generate Core for this instead:
Yes, I agree. That's what I meant in comment:14 with `fl_before` etc, but I expressed it badly. Let me try to do better. Accounting for monoidal's excellent point we could have {{{ data FractionalLit = FL { fl_text :: SourceText -- How the value was written in the source , fl_neg :: Bool -- See Note [Negative zero] , fl_mantissa, fl_exp :: Integer -- Denotes <mantissa>E<exp> } }}} So `1.077E400` would be represented with `fl_mantissa = 1077` and `fl_exp = 397`. Then we desugar to {{{ Var 'makeRational' `App` (Lit 1077) `App` (Lit 397) }}} where `makeRational` is a new library function defined thus {{{ makeRational :: Integer -> Integer -> Integer makeRational i e = (i % 1) * (10 ^^ e) }}} Probably we want it to inline, but that's a separate matter. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15646#comment:24 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler