[plt-scheme] Re: combinator-parser

From: Kathy Gray (kathryn.gray at cl.cam.ac.uk)
Date: Wed Mar 12 22:15:46 EDT 2008

On 3/12/08, Jon Zeppieri <zeppieri at gmail.com> wrote:
 > Does the combinator-parser library work?  The example (in
 > collects/combinator-parser/examples) doesn't, and I haven't been able
 > to make it work.

 > -Jon
Presently, while the parser combinator tools work, the documentation  
and examples are quite out of date and don't necessarily reflect what  
is required to build a working parser.

The primary change is that the current combinator is no longer in the  
lazy language; this impacts two factors that neither the current  
documentation, nor the example presents. First, the order now matters  
in linking and instantiating units; specifically in the example  
specification it is important that the link clause is the following  
(link combinator-parser-tools@ support lambda-calc). Second, some  
recursive grammar definitions now require the use of an eta expansion  
(using the provided eta operator to match the actual function  
signature of the combinators) to avoid additional undefined errors.  
The Java grammar specification (collects/profj/comb-parsers/parser- 
units.scm) is a more useful (although significantly more complex)  
example of a working parser specification.

(I can't recommend using the combinator-parser implementation from the  
non-svn-ed version; there are considerably more errors in the older  


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