I have defined a macro called @m.trial which simply escapes its argument and feeds into the @identity macro. The @identity macro is defined as (not escaped at the moment intentionally): macro identity(x) x end @m.trial a doesn’t work as expected. Lets define a=0 in the Main module. @m.trial @identity a gives the error that a is not defined. An inspection with @macroexpand shows that it looks a in the module m. I would assume that since @identity doesn’t escape its argument, one would get Main.a. If I define the unhygienic_identity macro: macro unhygienic_identity(x) esc(x) end Now modified trial macro @m.unhygienic_trial works. Now @m.foreach @unhygienic_identity a works. How exactly macro expansion happens ? I think this question is also related to the fact that escape expressions are not resolved before all macros are expanded. That is, @identity sees :($(Expr(:escape, :a))). module m macro trial(x) quote @Main.identity $(esc(x)) end end macro unhygienic_trial(x) quote @Main.unhygienic_identity $(esc(x)) end end end

Your hypothesis for the order of macro expansion expand @outer expand @inner apply hygiene for @inner apply hygiene for @outer agrees with my experiments. Have you noticed any inconsistencies with this hypothesis ?

Calling a macro within a macro

General Usage

johnmyleswhite March 24, 2021, 1:36am 2

One previous discussion of some issues involved here: Nested macros and esc

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Calling a macro within a macro

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