[Haskell-cafe] Unicode Haskell source -- Yippie!
daniel.is.fischer at googlemail.com
Wed Apr 30 09:03:45 UTC 2014
On Wednesday 30 April 2014, 13:51:38, Rustom Mody wrote:
> Without claiming to cover all cases, this is a 'principle'
> If we have:
> (⊞) :: a -> a -> b
> (⟐) :: b -> b -> c
> then ⊞'s precedence should be higher than ⟐.
But what if (⟐) :: b -> b -> a?
> This is what makes it natural to have the precedences of (+) (<) (&&) in
> decreasing order.
> This is also why the bitwise operators in C have the wrong precedence:
> x & 0xF == 0xF
> has only 1 meaningful interpretation; C chooses the other!
> The error comes (probably) from treating & as close to the logical
> operators like && whereas in fact it is more kin to arithmetic operators
> like +.
That comes from `&` and `|` being logical operators in B. Quoth Dennis Ritchie
(http://cm.bell-labs.com/who/dmr/chist.html in the section "Neonatal C"):
> to make the conversion less painful, we decided to keep the precedence of
> the & operator the same relative to ==, and merely split the precedence of
> && slightly from &. Today, it seems that it would have been preferable to
> move the relative precedences of & and ==, and thereby simplify a common C
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