An easier way of demonstrating this issue:
Prelude> [3,7..22]::[Int]
[3,7,11,15,19]
Prelude> [3,7..22]::[Double]
[3.0,7.0,11.0,15.0,19.0,23.0]
/Jonas
On 8 May 2010 09:47, Malcolm Wallace
Hugs> [3,7..22] [3,7,11,15,19] <- OK
Hugs> map (* 1.0) [3,7..22] <- same spec as first but !!! when mapped to with a (*1.0) to coerce them to reals: [3.0,7.0,11.0,15.0,19.0,23.0] <- went one outside of range spec.
This is because the Enum instance for floating point numbers is screwy and shouldn't be used in general
I think the original poster is probably being confused by the fact that the first mention of [3,7..22] looks identical to the second mention, but they are given different types by Haskell. The literal '3', although it looks like an integer, is being given the type Double in the second list enumeration, because of the context of needing to multiply it by 1.0. The comment mentions coercion, as if the list is generated at type Integer, and then converted to Double, but that is not the case. It is generated at type Double, and no coercion happens.
Regards, Malcolm
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