How to define a macro via Package Extension?

General Usage
1

I thought that you’d define functions my extending the original package’s functions like MyPackage.myfunc(::SpecialExtensionType) = ...

The same however does not work for macros

macro MyPackage.mymacro()
end

throws error ERROR: syntax: invalid macro definition ...

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2

What if your macro definition in the main package just calls a function that returns the corresponding expression, and then you just create a method for that function in the extension?

Many macro definitions already internally just call a function for generating the expression

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3

I feel hesitant to do so because then I need to decide “ahead” on the arguments, and cannot use dispatch here.

4

I actually found that you can extend macros by importing them.
import MyPackage: @mymacro
you then can extend the method table of the macro by defining simply

macro mymacro(#= ... =#)
    # ...
end
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5

Nice, you could also do something a bit more ugly without directly importing but your solution does look cleaner:

julia> module TESTT
       macro asd end
       end

julia> import .TESTT

julia> TESTT.var"@asd"(__source__::LineNumberNode, __module__::Module, x) = 15

julia> TESTT.@asd 0
15
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6

Why isn’t this allowed though? I thought it’d be an issue somewhere but couldn’t find one, just these barely related ones

Macro Inconsistency using Module Qualification · Issue #32301 · JuliaLang/julia · GitHub

macro qualification inconsistency · Issue #1769 · JuliaLang/julia · GitHub

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7

It’s worth noting that for the definition that needs to be in the base package itself, much like you can do

function foo end

you can do

macro foo end
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8

wooooo!! I always thought that it would make sense to treat macros as functions with extra arguments, but never thought that it is already the case!

9

I am also surprised. Looks like an inconsistency for me.

Thanks for the research. I created a new issue now

10

If I have to guess, it’s because macros couldn’t be extended at all until late in the pre-v1 development: for a long time there could be a single method for macros, so extending them made little sense, let alone in a different module.

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