On 28 May 2008, at 09:34, PR Stanley wrote:
Hi (16 :: Float) is a perfectly legitimate statement although I'm surprised that it's allowed in a type strong language such as Haskell. It's a bit like casting in good old C. What's going on here?
It's not a coercion -- it happens at compile time. In a coercion, 16 starts off it's runtime life as an integer, gets a couple of things done to it, and then is coerced into a floating point number. What's happening here is you are telling the compiler "I would like the number 16, but a floating point version of it please". That instance of 16 always will have type Float. Slightly more detail: numeric literals like this normally have the type Int, but get pre-processed by the compiler. Whenever you write 16, the compiler writes (fromInteger 16). This has the effect that instead of having the type Int, your literal has the type Num a => a. You adding the type signature constrains it to being a Float again. Bob