Local macros

General Usage
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In CommonLisp one can define local macros using MACROLET. Julia doesn’t have local macros, but one can imagine that a given global macro could provide local macros for use wwithin its body using a code walker and rules that re-write :macrocall expressions.

Has anyone already implemented such a utility?

It seems straightforward enough, but I imagine there might be unforseen pitfalls.

What’s the problem I’m immediately trying to solve via local macros? I have a simple-minded expert system shell (Rete.jl) with an @rule macro. That macro implements an install method which will connect a new join node that implements the rule into a discrimination network. The body of a rule performs some conditionals and if all succeed then the rule will emit new facts to the network. Currently there are no diagnostics if a rule fails to make an expected conclusion if one of the conditionals fails because the join function just returns. I want there to be something (a local macro) that takes a predicate and logs when the predicate fails before the rule body exits.

This could be done with a closure but I want the log message to include the predicate expression and the source location.

I’m currently looking at both MacroTools and SymbolicUtils.

Any suggestions or insights?

Thanks.

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Macros are scoped to locally to modules in Julia.

I don’t understand why your @rule macro couldn’t do this — why can’t it pass the predicate expression and the source location to the closure or whatever data structure you are using?

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Perhaps I’m not being clear.

I’m proposing to walk the body of the @rule macro call and rewrite certain macrocall expressions like @rejectif, thus emulating a local macro mechanism.

I was wondering if someone had already implemented such a thing.

I’ve tried using MacroTools for the pattern matching, but the general method on match_inner removes line number nodes. I guess I’ll need to write my own matcher.

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I once did this inside out macro which seems related jkrumbiegel.com – Composing macros inside-out with Julia