On 10 feb 2010, at 10:40, Sebastian Fischer wrote:
On Feb 9, 2010, at 10:43 PM, S. Doaitse Swierstra wrote:
-- but if we now unfold the definition of one we get a parser error
in GHC
increment' = ( let x=1 in x + )
The GHC and Hugs parsers are trying so hard to adhere to the meta
rule that bodies of let-expressions
extend as far as possible when needed in order to avoid ambiguity,
that they even apply that rule when there is no ambiguity;
here we have only a single possible parse, i.e. interpreting the
offending expression as ((let x = 1 in ) +).
Despite the fact that there is a typo (second x is missing), I can
think of two possible parses. Actually, my mental parser produced
the second one:
((let x=1 in x)+)
let x=1 in (x+)
The Haskell report may exclude my mental parse because operator
sections need to be parenthesised.
Indeed, but it is not "may exclude", but "excludes".
Or are you arguing that in your example different possible parses
have the same semantics for an arguably obvious reason and that this
fact is relevant?
No,
Doaitse
Sebastian
--
Underestimating the novelty of the future is a time-honored tradition.
(D.G.)
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