Many apologies for triple posting - short-circuit between ears.
Peri Hankey
--
http://languagemachine.sourceforge.net - The language machine
Dave Whipp wrote:
If I want to parse a language that is sensitive to whitespace
indentation (e.g. Python, Haskell), how do I do it using P6 rules/grammars?
The way I'd usually handle it is to have a lexer that examines leading
whitespace and converts it into "indent" and "unindent" tokens. The
Dave Whipp wrote:
If I want to parse a language that is sensitive to whitespace
indentation (e.g. Python, Haskell), how do I do it using P6
rules/grammars?
The way I'd usually handle it is to have a lexer that examines leading
whitespace and converts it into "indent" and "unindent" tokens. T
Dave Whipp wrote:
If I want to parse a language that is sensitive to whitespace
indentation (e.g. Python, Haskell), how do I do it using P6 rules/grammars?
The way I'd usually handle it is to have a lexer that examines leading
whitespace and converts it into "indent" and "unindent" tokens. The
Damian Conway wrote:
Alternatively, you could define separate rules for the three cases:
{
state @indents = 0;
rule indent {
^^ $:=(\h*)
{ $ = expand_tabs($).chars }
<( $ > @indents[-1] )>
{ let @indents = (@indents, $) }
On 9/8/05, Larry Wall <[EMAIL PROTECTED]> wrote:
> Okay, how do you tell the difference between
>
> if foo1
> bar1
> if foo2
> bar2
> if foo3
> bar3
> else
>
On Thu, Sep 08, 2005 at 07:57:43PM -0400, Collin Winter wrote:
: On 9/8/05, Larry Wall <[EMAIL PROTECTED]> wrote:
: > It seems to me you need a stack of levels so you know how many
: > indentation levels to pop off. Otherwise you can't parse this:
: >
: > if foo1
: > bar1
On 9/8/05, Larry Wall <[EMAIL PROTECTED]> wrote:
> It seems to me you need a stack of levels so you know how many
> indentation levels to pop off. Otherwise you can't parse this:
>
> if foo1
> bar1
> if foo2
> bar2
>
To solve Dave's particular problem, you don't need any new features. Just:
rule indentation {
^^ $:=(\h*)
{ state @indents = 0;
my $new_indent = expand_tabs($).chars;
let @indents = @indents;
pop @indents while @indents && $new_indent <= @
On Thu, 2005-09-08 at 14:59 -0700, Greg Woodhouse wrote:
> I agree that simply using terms like this means indentation grammars
> are problematic -- or does it? One thing that bothers me is that
> *people* don't seem to have a great deal of difficulty with them. Why
> not?
People can parse multi-
Come to think of it...I had in mind a sequence of "skip" statements,
that would back out of a level one at a time, until you finally reached
the desired level. But, I think maybe these "skip" statements
essentially play the role of what you called "positive unindent tokens"
(I like that term).
I a
What I had in mind is really no different from the stateful lexer
previously proposed. Unless I'm mistaken, an abstract model might be a
language over {0, 1, 2} where each 1 or 2 must be prececed by a run of
1 or more 0's, but each run differ in length from the preceding one by
0, 1 or -1. But that
On Thu, Sep 08, 2005 at 02:16:33PM -0700, Greg Woodhouse wrote:
: In the case of the
: "indentation grammar", then the (one) stack in a push-down automaton is
: basically used up keeping track of the indentation level. But you don't
: need a whole stack to keep track of indntation level, just a reg
That's something I've been thinking about, too. There are a lot of
"interesting" languages that cannot be described by context free
grammars (such as {empty, 012, 001122, 000111222, ...} but very simple
enhancements do make them easy to recognize. In the case of the
"indentation grammar", then the
On Thu, Sep 08, 2005 at 08:37:21AM -0700, Dave Whipp wrote:
: If I want to parse a language that is sensitive to whitespace
: indentation (e.g. Python, Haskell), how do I do it using P6 rules/grammars?
:
: The way I'd usually handle it is to have a lexer that examines leading
: whitespace and co
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