Ross points out that this is really hard to parse:
| case x of y | ($ True) $ \ z - z :: Bool - Bool - y
because the parser doesn't know when to stop eating the type
and treat the arrow as the case-alternative arrow.
Carl reminds us that this is hard to parse too:
| do a == b == c
Simon Peyton-Jones [EMAIL PROTECTED] writes:
I didn't phrase it right. I meant that a let/lambda/if always
extends to the next relevant (not part of a smaller expression)
punctuation symbol; and if that phrase parses as an exp
that's fine, otherwise it's a parse error. So I should not
On Wed, Feb 27, 2002 at 06:45:45AM -0800, Simon Peyton-Jones wrote:
So I propose to say that 'let', 'lambda' and 'if' productions have
a side condition that (say)
let .. in exp
is syntactially valid only if the phrase is followed by one of the
punctuation symbols
) ] } | ;
On Tue, Feb 26, 2002 at 08:23:03AM -0800, Simon Peyton-Jones wrote:
I didn't phrase it right. I meant that a let/lambda/if always
extends to the next relevant (not part of a smaller expression)
punctuation symbol; and if that phrase parses as an exp
that's fine, otherwise it's a parse
PROTECTED]]
| Sent: 27 February 2002 10:43
| To: Simon Peyton-Jones
| Cc: [EMAIL PROTECTED]
| Subject: Re: H98 Report: expression syntax glitch
|
|
| On Tue, Feb 26, 2002 at 08:23:03AM -0800, Simon Peyton-Jones wrote:
| I didn't phrase it right. I meant that a let/lambda/if always
| extends
On Wed, Feb 27, 2002 at 04:00:39PM +0100, Arthur Baars wrote:
In the context-free grammar proposed by Ross Paterson
the following line:
expix - expi+1B [qop(n,i) expi+1x]
should be replaced by
expix - [expi+1B qop(n,i)] expi+1x
Yes. (In fact that's what I had in the revised hssource
On Mon, Feb 25, 2002 at 04:30:24PM +, Malcolm Wallace wrote:
Yes, but it reports type errors for the variants
f x = (\x - x*x .)
g x = (if x then 1 else 2 +)
and it accepts
h = (let op x y = y in 3 `op`)
so I suspect it's misparsing these as
f x = (\x - (x*x .))
On Mon, Feb 25, 2002 at 04:27:56PM -, Simon Marlow wrote:
This is a known problem with the Haskell grammar. Another example in
a similar vein is
let x = 3 in x == 4 == True
which should parse as
(let x = 3 in x == 4) == True
according to the extends as far to the
On Mon, Feb 25, 2002 at 05:07:35PM -, Simon Marlow wrote:
On the other hand, one way to fix this problem *is* to specify the
relative precedence of 'let' co. as compared to infix operators
(namely that 'let' should have a lower precedence). That would be a
reasonable fix for the
| Consider the following Haskell 98 expressions:
|
| (let x = 10 in x `div`)
| (let x = 10 in x `div` 3)
|
| To parse the first, a bottom-up parser should reduce the
| let-expression before the operator, while to parse the second
| it should shift. But it needs 4 tokens of
On Tue, Feb 26, 2002 at 07:30:44AM -0800, Simon Peyton-Jones wrote:
Replace The ambiguity is resolved by the meta rule that each of these
constructs extends as far to the right as possible by
The ambiguity is resolved by the meta rule that each
of these constructs extends to
| -Original Message-
| From: Ross Paterson [mailto:[EMAIL PROTECTED]]
| Sent: 26 February 2002 16:06
| To: Simon Peyton-Jones
| Cc: [EMAIL PROTECTED]
| Subject: Re: H98 Report: expression syntax glitch
|
|
| On Tue, Feb 26, 2002 at 07:30:44AM -0800, Simon Peyton-Jones wrote:
| Replace The ambiguity
On Mon, Feb 25, 2002 at 03:38:39PM +, Malcolm Wallace wrote:
nhc98 manages to parse and compile both expressions with ease, no doubt
because it uses parser combinators rather than a table-driven mechanism.
Yes, but it reports type errors for the variants
f x = (\x - x*x .)
In the table of precedence in the original Report (now deleted in
the revised Report), it makes it clear that a rightward-extending
let, if, or lambda has a lower precedence than an infix operator,
so for instance the parse
h = (let op x y = y in (3 `op`))
is correct and
On Mon, Feb 25, 2002 at 05:07:35PM -, Simon Marlow wrote:
On the other hand, one way to fix this problem *is* to specify the
relative precedence of 'let' co. as compared to infix operators
(namely that 'let' should have a lower precedence). That would be a
reasonable fix for the H98
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