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by lispm 5719 days ago
Read tables existed before CL. CLOS for example not, it was developed for ANSI CL (based on experience with LOOPS and Flavors). See for example READTABLE in Maclisp:

http://maclisp.info/pitmanual/io.html#16.2.7

Also note that I wrote that the API is ancient. It is. It is old and could be easier to use.

'Named readtables' are related to 'syntaxes' on the Lisp Machine. For example source files have a syntax attribute in the header, which switches between the various Lisp dialects (or other languages), including using different readers. This is for example used by the file compiler and Zmacs.
1 comments
sedachv 5719 days ago
Cool, I didn't know readtables were in Maclisp, or about LM syntaxes.

"It is old and could be easier to use."

Aside from something like named-readtables, how would you design the lowest-level interface to readtables? Or you wouldn't do that, and just specify something like named-readtables to be the interface? I'm curious because this could be something for http://www.cliki.net/Proposed%20Extensions%20To%20ANSI

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lispm 5719 days ago
I haven't thought about it much, but the character level interface is very primitive. Second, what about things like symbols, numbers, etc.? There is no sane way to specify number syntax or symbol syntax. That might be useful. Currently the reader provides an interface on a character level, but not on the level of s-expressions components.
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sedachv 5719 days ago
What I think you're saying is that the reader should be customizable in terms of some DSL for a grammar. It would be nice, but I'm not sure how composable it would be (in the general case, I think it would come down to having the behavior of READ dependent upon a black-box current-parser procedure).

The nice thing about readtables is that it exposes what in essence are transition hooks for each character, so you really don't need to care about the grammar of stuff you're not interested in parsing.

OTOH like you said, extending the syntax for numbers or symbols becomes quite hairy. But even with a DSL grammar approach, you'd need to change major parts of the grammar (which means copying and modifying the normative grammar of CL syntax - not that different from grabbing a portable CL reader implementation today (http://twitter.com/vsedach/status/26484049015)).

The big downside is deciding on which class of grammars that will support, and how they will be represented.

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