[Haskell-cafe] map (-2) [1..5]

[Brian Hulley]

Jared Updike wrote:
>> I'd also argue that in maths the necessary brackets are implied by
>> the superscripting syntax
>
> ASCII text parsing issues aside, in math,
>
>    2
> -4           =    ?
>
> (No you cannot ask if there is space between the 4 and the - symbol,
> or if I "meant" (-4)^2   or -(4^2), or if I wrote a negative sign or a
> subtract sign. I believe there is only one standard interpretation
> here.)

Yes but my point is that -4^2 is not the same as

                2
            -4

because the latter by convention means - (4^2).

In other words, superscripts bind tighter than prefix ops but prefix ops 
bind tighter than infix.

>
>> they can only get in through the "back door" of evaluation
>> which just doesn't seem right.
>
> Constant folding can eliminate any runtime cost, so effectively 0 - 2
> ==> negative 2 at compile time. No problem.

An Int8 has the range -128 to +127 inclusive, so I'd have expected a problem 
with the expression

    negate (128 :: Int8)

However I see from 
http://en.wikipedia.org/wiki/Two's_complement#The_weird_number that this 
works because -128 === +128 ie

               negate (128::Int8)
    ===    negate (-128)    -- literal to typed value
    ===    (+128)              -- negation
    ===    (-128)               -- overflow ignored

Regards, Brian.
-- 
Logic empowers us and Love gives us purpose.
Yet still phantoms restless for eras long past,
congealed in the present in unthought forms,
strive mightily unseen to destroy us.

http://www.metamilk.com