Re: Generalized parser without generation

James Moughan <moughanj@tcd.ie> wrote:
> A friend of mine has been given a final year project for which his
> supervisor wants the above; that is, a program which can read in a
> description of a grammar then parse a file using it directly. Users
> must be able to add new grammars at any time without compiling.


You can do this sort of thing with an Earley parser or a generalized
recursive descent parser (something like what boost::spirit does). An
Earley parser is a bit harder to write, but supports left-recursion
and ambiguity better than a recursive descent parser.


> James Moughan
> [Extensible parsers that could add new syntax on the fly were popular in
> the 1970s, but I haven't seen any lately. They turned out to be useful
> for writing code that nobody could read, but not for much else. -John]


What about Dylan? It places some limits on the kinds of things you can
define, but even with those in place you can create an awful lot of
new syntax.


    -- Jesse

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