#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 osa1):
The literal 1e100 means fromRational (100...000 :: Rational), as specified in Haskell report
Where is this specified in the report? I can see the syntax in section 2.5 which links to sections 3.4 and 6.4.1 but I can't see this rule in any of those linked sections. Can't find where the semantics for this literal is defined.
It's not surprising it crashes badly when the exponent has 10 digits or more.
Wait, are you saying that typing `1e1234111111111111111111111` to take minutes and use up more than 20G of memory (residence, not allocation!) not surprising? Perhaps I'm completely lost then. Could you elaborate on how is this not surprising? FWIW I just typed in that expression in Python REPL and it gave me an answer in an instant.
With -XNumDecimals, we need to process the literal before we can tell its type: 1.234e3 is a valid Integer but 1.234e2 is not.
I'm still not convinced that we can't do better but OK. At the very least we should be able to type those expressions quickly when `-XNumDecimals` is not enabled (which is the default). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15646#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler