#13124: Template Haskell: Floating point literals that cannot be represented by rationals -------------------------------------+------------------------------------- Reporter: lerkok | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by rwbarton):
One can easily imagine doing a similar transformation via TH, and having access to arbitrary floating constants would be useful. There would be no easy way to write that in TH today as all the "magic" constants would have to be converted to rationals, thus having anomalies.
I wouldn't go as far as saying that this is a huge shortcoming, but I don't see why TH can't just use a good old double/float there instead of requiring a Rational? Is there a good reason for requiring a Rational
This doesn't make sense to me: any ordinary floating point value (i.e. not negative zero, infinity or NaN) can be exactly represented as a rational number. For those special floating point values, you could just generate an expression that evaluates to the `Double` you need, like `1.0 / 0.0`. Do you really need a literal specifically? In short, I don't see a real use case here. there? GHC doesn't use `Double` in any AST type. All floating point literals are represented internally as `Rational`. Considering the nasty and potentially platform-dependent semantics of `Double`, this is a good thing. Imagine cross-compiling to a hypothetical platform with 128-bit `Double`s on a platform that doesn't support that. (It's also certainly necessary to represent floating-point literals as `Rational` rather than `Double` or any other fixed-size data type, since `Rational` is itself a valid type for a floating-point literal!) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13124#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler