RE: [Haskell-cafe] Parsec Expected Type
Thanks. reservedOp is a better fit; :+ should only be :+. I also overcame my type issues in an ad-hoc manner, adding return () whenever I needed to. -Original Message- From: Tillmann Rendel [mailto:[EMAIL PROTECTED] Sent: 30 March 2008 12:30 To: Paul Keir; haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] Parsec Expected Type Paul Keir wrote: What I'd like is to parse either the string parameter, or the string :. I'm using 'reserved' and 'symbol' because they seem to correspond well to the concepts in the language I'm parsing. You may consider using reservedOp for :, depending on how :+ should be parsed: for :+ use reservedOp for : + use symbol If you use reserved, then :name will be parsed as :name not : name as you probably expect. generally, reserved is for identifier-like keywords, and reservedOp for operator-like keywords. Perhaps I'd express my confusion better if I ask: Why are 'reserved' and 'symbol' different types? I have no idea. They aren't in the Parsec manual on Daans site: http://legacy.cs.uu.nl/daan/download/parsec/parsec.html You can fix this by defining reserved name = ParsecToken.reserved tokenParser name return name instead of reserved = ParsecToken.reserved tokenParser to import the reserved component from the tokenParser to the toplevel. Now, reserved :: String - CharParser st String Another option is to fix it the other way, by defining symbol name = ParsecToken.symbol tokenParser name return () or to fix it in a ad-hoc manner, by defining ignored = ( return ()) and using it in the approbiate places, like parameterOrColon = reserved parameter | ignored (symbol :) Tillmann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Parsec Expected Type
Paul Keir wrote: What I'd like is to parse either the string parameter, or the string :. I'm using 'reserved' and 'symbol' because they seem to correspond well to the concepts in the language I'm parsing. You may consider using reservedOp for :, depending on how :+ should be parsed: for :+ use reservedOp for : + use symbol If you use reserved, then :name will be parsed as :name not : name as you probably expect. generally, reserved is for identifier-like keywords, and reservedOp for operator-like keywords. Perhaps I'd express my confusion better if I ask: Why are 'reserved' and 'symbol' different types? I have no idea. They aren't in the Parsec manual on Daans site: http://legacy.cs.uu.nl/daan/download/parsec/parsec.html You can fix this by defining reserved name = ParsecToken.reserved tokenParser name return name instead of reserved = ParsecToken.reserved tokenParser to import the reserved component from the tokenParser to the toplevel. Now, reserved :: String - CharParser st String Another option is to fix it the other way, by defining symbol name = ParsecToken.symbol tokenParser name return () or to fix it in a ad-hoc manner, by defining ignored = ( return ()) and using it in the approbiate places, like parameterOrColon = reserved parameter | ignored (symbol :) Tillmann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Parsec Expected Type
Many thanks guys, you've really taught me how to catch a fish here!
Paul
-Original Message-
From: Brandon S. Allbery KF8NH [mailto:[EMAIL PROTECTED]
Sent: Sat 3/29/2008 1:41 AM
To: haskell-cafe@haskell.org Cafe
Cc: Paul Keir
Subject: Re: [Haskell-cafe] Parsec Expected Type
On Mar 28, 2008, at 21:12 , Ryan Ingram wrote:
On 3/28/08, Paul Keir [EMAIL PROTECTED] wrote:
What I'd like is to parse either the string parameter, or the
string :.
I'm using 'reserved' and 'symbol' because they seem to correspond
well to
the concepts in the language I'm parsing. I could try,
tester3 = reserved parameter | do { symbol :; return () }
Or you could factor this behavior out into a new combinator:
or_ :: Parser a - Parser b - Parser ()
or_ x y = (x return ()) | (y return ())
tester3 = reserved parameter `or_` symbol :
Or if you'd like to be inscrutable:
import Data.Function
or_ = ( return ()) `on` (|)
--
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED]
system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED]
electrical and computer engineering, carnegie mellon universityKF8NH
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RE: [Haskell-cafe] Parsec Expected Type
Thanks, I'd thought it was something to do with incompatible types. I can now
create a simpler problem:
tester2 = reserved parameter | symbol :
Certainly I could use reserved : instead of symbol, but where is my thinking
with symbol here going wrong? Surely the above example isn't so odd?
Paul
-Original Message-
From: Luke Palmer [mailto:[EMAIL PROTECTED]
Sent: Fri 3/28/2008 12:26 AM
To: Paul Keir
Cc: haskell-cafe@haskell.org
Subject: Re: [Haskell-cafe] Parsec Expected Type
Hi Paul,
2008/3/27 Paul Keir [EMAIL PROTECTED]:
Hi,
Does anyone know why this reduced Parsec production stops compilation, and
how I can fix it?
tester = reserved parameter
| do { reserved dimension; symbol : }
Look at the types of reserved and symbol (from
http://www.haskell.org/ghc/docs/latest/html/libraries/parsec/Text-ParserCombinators-Parsec-Token.html):
symbol :: String - CharParser st String
reserved :: String - CharParser st ()
The type of a do block is the same as the type of its last statement.
But (reserved parameter) and (symbol ;) do not have the same type.
Luke
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Re: [Haskell-cafe] Parsec Expected Type
On 28 Mar 2008, at 2:02 AM, Paul Keir wrote: Thanks, I'd thought it was something to do with incompatible types. I can now create a simpler problem: tester2 = reserved parameter | symbol : Certainly I could use reserved : instead of symbol, but where is my thinking with symbol here going wrong? Surely the above example isn't so odd? What type do you expect tester2 to return? jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Parsec Expected Type
Could tester2 return some kind of base type, which the two inherit from? I
don't know. I'm really only presenting the ugly tester2 function because I'm
looking for a Parsec-concordant solution to what appears a simple problem.
What I'd like is to parse either the string parameter, or the string :. I'm
using 'reserved' and 'symbol' because they seem to correspond well to the
concepts in the language I'm parsing. I could try,
tester3 = reserved parameter | do { symbol :; return () }
but that's feels a bit contrived; or I could use 'reserved' twice.
Perhaps I'd express my confusion better if I ask: Why are 'reserved' and
'symbol' different types?
Paul (Haskell Novice)
-Original Message-
From: Jonathan Cast [mailto:[EMAIL PROTECTED]
Sent: Fri 3/28/2008 2:05 PM
To: Paul Keir
Cc: Luke Palmer; haskell-cafe@haskell.org
Subject: Re: [Haskell-cafe] Parsec Expected Type
On 28 Mar 2008, at 2:02 AM, Paul Keir wrote:
Thanks, I'd thought it was something to do with incompatible types.
I can now create a simpler problem:
tester2 = reserved parameter | symbol :
Certainly I could use reserved : instead of symbol, but where is
my thinking with symbol here going wrong? Surely the above example
isn't so odd?
What type do you expect tester2 to return?
jcc
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Re: [Haskell-cafe] Parsec Expected Type
On 3/28/08, Paul Keir [EMAIL PROTECTED] wrote:
What I'd like is to parse either the string parameter, or the string :.
I'm using 'reserved' and 'symbol' because they seem to correspond well to
the concepts in the language I'm parsing. I could try,
tester3 = reserved parameter | do { symbol :; return () }
Actually this is exactly on the right track. But I agree, it looks a
bit contrived. Maybe this looks better to you?
tester3 = reserved parameter | (symbol : return ())
Or you could factor this behavior out into a new combinator:
or_ :: Parser a - Parser b - Parser ()
or_ x y = (x return ()) | (y return ())
tester3 = reserved parameter `or_` symbol :
-- ryan
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Re: [Haskell-cafe] Parsec Expected Type
On Mar 28, 2008, at 21:12 , Ryan Ingram wrote:
On 3/28/08, Paul Keir [EMAIL PROTECTED] wrote:
What I'd like is to parse either the string parameter, or the
string :.
I'm using 'reserved' and 'symbol' because they seem to correspond
well to
the concepts in the language I'm parsing. I could try,
tester3 = reserved parameter | do { symbol :; return () }
Or you could factor this behavior out into a new combinator:
or_ :: Parser a - Parser b - Parser ()
or_ x y = (x return ()) | (y return ())
tester3 = reserved parameter `or_` symbol :
Or if you'd like to be inscrutable:
import Data.Function
or_ = ( return ()) `on` (|)
--
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED]
system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED]
electrical and computer engineering, carnegie mellon universityKF8NH
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Re: [Haskell-cafe] Parsec Expected Type
Hi Paul,
2008/3/27 Paul Keir [EMAIL PROTECTED]:
Hi,
Does anyone know why this reduced Parsec production stops compilation, and
how I can fix it?
tester = reserved parameter
| do { reserved dimension; symbol : }
Look at the types of reserved and symbol (from
http://www.haskell.org/ghc/docs/latest/html/libraries/parsec/Text-ParserCombinators-Parsec-Token.html):
symbol :: String - CharParser st String
reserved :: String - CharParser st ()
The type of a do block is the same as the type of its last statement.
But (reserved parameter) and (symbol ;) do not have the same type.
Luke
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