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0 pointsmalisper11y ago0 comments

Well iterate[0], which is a lispy version of loop, is actually extendable through macros[1]. So what you are looking for is just a generic way to enable that for all macros? Iterate does it by having a code walker go over the code and macroexpand the extendable parts. It shouldn't be too hard to apply that method to new DSLs by specifying the syntax of the DSL to the code walker.

[0] https://common-lisp.net/project/iterate/

[1] https://common-lisp.net/project/iterate/doc/Rolling-Your-Own...

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rntz11y ago

Yup, I pretty much want it to be trivially easy for define macros that are themselves macro-extensible. It's definitely possible to do this in Lisp, but:

(a) it's not a well-known technique

(b) it's not in the standard library of any Lisp I know of

I hope this article will get folks thinking about these issues.

For example, walking the AST and calling macroexpand will work, but then you can't have a macro that expands differently in different contexts - when interpreted as an expression versus as a pattern, for example. I think this is an important feature.

malisperOP11y ago

> you can't have a macro that expands differently in different contexts

This[0] may be of some help. You could set it to expand macros differently according to the current context (some global variable).

You could also write your own macroexpand function which would default to the implementation's macroexpand.

This is definitely something interesting to think about. Thank you for the discussion.

[0] http://www.ai.mit.edu/projects/iiip/doc/CommonLISP/HyperSpec...

DalekBaldwin11y ago

The macroexpansion hook isn't nearly as powerful or useful as it could be because the process of macroexpansion is not recursive. Although expansion functions can access information about the lexical environment via an &environment parameter, the invocations of those expansion functions do not share any dynamic context with other invocations at nodes above or below them in the syntax tree.

Here's a more thorough summary of the problem: http://qiita.com/guicho271828/items/07ba4ff11bff494dc03f

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