The following header lines retained to affect attribution: |Date: Sun, 2 Mar 1997 13:48:57 +0100 |From: Hans Aberg <[log in to unmask]> |Subject: Re: Shortref mechanism |Frank Mittelbach <[log in to unmask]> wrote: |>The above means that the shortref mechanism either has to be fully |>expandable or that one can't use it to produce glyphs that might play |>a part in ligature or kerning tables. | I cannot follow the details in your reasoning, but I can note that with |deterministic parsing, the method generally used in LaTeX, conditional ^^^^^^^^^^^^^ ^^^^^^^ ^^^^^^^^^^^ |parsing have such limits. ^^^^^^^ | But with non-deterministic parsing more general things can be done: ^^^^^^^^^^^^^^^^^ | For example, I just made a definition command that can produce commands |having optional arguments; in this general approach, I had to switch from |LaTeX style deterministic parsing to non-deterministic parsing. ^^^^^^^^^^^^^ ^^^^^^^ ^^^^^^^^^^^^^^^^^ ... | Hans Aberg To someone that has written several small compilers and has studied automata theory at the doctorate level, your word choice as high-lighted above is quite jarring. By using a power automaton, a non-deterministic automaton can be reduced to a deterministic automaton. Therefore, one does not gain any power of expression by using a non-deterministic automaton, rather one only gains compaction of the description. I believe that what you intended is the distinction of context free and context sensitive languages. From what I have read in the TeX book, the tokenizer of TeX is context sensitive with a single character look-ahead and the TeX language based on the recognized tokens is context free. It is a significant change in the behavior of the TeX language to change it from being context free to being context sensitive. But, it may be a necessary change. Most modern computer languages are context sensitive with a single token look ahead. A few look ahead two tokens in some situations. I imagine that some look ahead three tokens. Parser generators for single token look ahead readily are availed. What you are proposing is a change from zero token look ahead to one token look ahead. Randolph J. Herber, [log in to unmask], +1 630 840 2966, CD/OSS/CDF CDF-PK-149O Mail Stop 234 Fermilab, Kirk & Pine Rds., P.O. Box 500, Batavia, IL 60190-0500. (Speaking for myself and not for US, US DOE, FNAL nor URA.) (Product, trade, or service marks herein belong to their respective owners.) N 41 50 26.3 W 88 14 54.4 and altitude 700' approximately, WGS84 datum.