Second draft of the Haskell 2010 report available

Simon Marlow marlowsd at
Wed Jul 7 15:32:25 EDT 2010

On 07/07/10 16:56, Christian Maeder wrote:
> Simon Marlow schrieb:
>> prefix negation should move to lexp to
>> be consistent with lpat
> prefix negation should not move to lexp, because this would rule out
> "- 1 ^ 2" as negated infix expression "- (1 ^ 2)",

It wouldn't - remember the grammar just parses infix expressions as a 
list, they get rearranged by fixity resolution.

I'm arguing that the current grammar is halfway between two consistent 
positions: one in which prefix negation is lexp, the other is your 
proposal to make the grammar ambiguous.  So we should do one or the other.

> whereas a negated
> infix pattern is impossible. Unary minus is no constructor and cannot be
> defined. The latter should be (or is already?) mentioned somewhere.
> You could move prefix negation to lexp, if you allow the fixity
> resolution to construct negated infix expression that are not covered by
> the grammar (as currently happens anyway).

Right, that's what I'm saying.  No change needed to fixity resolution, 
just move prefix negation into lexp.

> Moving prefix negation from lpat to pat to be consistent with infixexp
> would be overkill, though.



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