Parsec-2 versus Parsec-3

[Christian Maeder]

Hi,

I had a look at parsec-3 and my (first) impression was a shock to see in
http://hackage.haskell.org/packages/archive/parsec/3.1.0/doc/html/src/Text-Parsec-Prim.html

<cite>
-- Portability :  portable
[...]
{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies,
FlexibleContexts,
             UndecidableInstances #-}
</cite>

whereas the (old) documentation at
http://legacy.cs.uu.nl/daan/download/parsec/parsec.html
says:

<cite>
Compatibility
The core library is written in Haskell98.
</cite>

This alone is a reason to prefer parsec-2 over parsec-3.

I don't mind more generality for a small speed penalty, but this
non-Haskell98 monad-transformer stuff (that I don't need, yet) and that
is only documented in a blog (without link from the sources) should be
in a separate module (if not package)!

I've tried out the compatibility layer. Compiling and parsing works
identical for my test cases, but some error messages are different
(differences below)!

This compatibility layer is useful for testing, but I would not mind to
change (or expand) my imports, therefore I think the compatibility layer
should also be a separate package. (For some reason I don't like modules
much that re-export functions from underlying modules.)

Cheers Christian

- parsec-2
+ parsec-3.1.0


 parse error at 2.2:

-unexpected "1"

-expecting "{", "[", __ or end of input

+unexpected '1'

+expecting end of input



 parse error at 3.2:

-unexpected "."

-expecting "{", "[", __ or end of input

+unexpected '.'

+expecting end of input



 parse error at 4.2:

 unexpected "'"

@@ -49,8 +49,8 @@

 expecting id



 parse error at 14.2:

-unexpected "b"

-expecting "{", "[", __ or end of input

+unexpected 'b'

+expecting end of input



 parse error at 15.1:

 unexpected "as"

@@ -64,9 +64,9 @@
 unexpected "_"
 expecting id

-parse error at 18.4-18.5:
-unexpected "_"
-expecting casl char, "{", "[", __ or end of input
+parse error at 18.4:
+unexpected '_'
+expecting end of input

 parse error at 19.3:
 unexpected end of input
@@ -141,24 +141,24 @@
 expecting id

 parse error at 37.15:
-unexpected "<"
-expecting __ or end of input
+unexpected '<'
+expecting end of input

 parse error at 38.4:
-unexpected "="
-expecting "{", "[", __ or end of input
+unexpected '='
+expecting end of input

 parse error at 39.6:
-unexpected "%"
-expecting __ or end of input
+unexpected '%'
+expecting end of input

 parse error at 40.1:
 unexpected "\""
 expecting id

 parse error at 41.8:
-unexpected ">"
-expecting __ or end of input
+unexpected '>'
+expecting end of input