Ahh nice, thanks. Your macrocall suggestions reads cleanly too, I think
it'd look something like this:
julia> macro macrocall(mac,args...)
Expr(:macrocall,esc(mac),map(esc,args)...)
end
@macrocall (macro with 1 method)
julia> @macrocall idmacro 1+2
3
What's the problem with local variables you mention though? I can't think
of where this wouldn't work.
On Sunday, September 25, 2016 at 2:08:46 PM UTC+2, Yichao Yu wrote:
>
> On Sun, Sep 25, 2016 at 7:25 AM, Marius Millea <marius...@gmail.com
> <javascript:>> wrote:
> > I can store a macro to a variable (let use the identity macro "id" as an
> > example),
> >
> > julia> idmacro = macro id(ex)
> > :($(esc(ex)))
> > end
> > @id (macro with 1 method)
> >
> >
> > How can I use this macro now? I can *almost* do it by hand by passing an
> > expression as an argument and eval'ing the result, but it doesn't work
> > because there's esc's left,
>
> Assuming this is just for understanding how macros are implemented,
> you can just construct a microcall expression
>
> julia> idmacro = macro id(ex)
> esc(ex)
> end
> @id (macro with 1 method)
>
> julia> idmacro(:(1 + 2))
> :($(Expr(:escape, :(1 + 2))))
>
> julia> eval(Expr(:macrocall, :idmacro, :(1 + 2)))
> 3
>
> This is unlikely what you want to do in real code.
>
> Side notes,
>
> As shown above, you can just do `esc(ex)`, `:($foo)` is equivalent to
> `foo`
>
> You can also use a variable name starts with `@` since that's the
> syntax that triggers the parsing to a macrocall expression.
>
> julia> eval(:($(Symbol("@idmacro")) = idmacro))
> @id (macro with 1 method)
>
> julia> @idmacro 1 + 2
> 3
>
> julia> Meta.show_sexpr(:(@idmacro 1 + 2))
> (:macrocall, Symbol("@idmacro"), (:call, :+, 1, 2))
>
>
> You can do this transformation with a macro too (i.e. make @macrocall
> idmacro 1 + 2 construct a macrocall expression) but it's not really
> useful since you can't do this for a local variable, which is also why
> I said don't do this in real code.
>
> >
> > julia> @id 1+2
> > 3
> >
> >
> > julia> idmacro(:(1+2))
> > :($(Expr(:escape, :(1 + 2))))
> >
> >
> > julia> eval(idmacro(:(1+2)))
> > ERROR: syntax: unhandled expr (escape (call + 1 2))
> > in eval(::Module, ::Any) at ./boot.jl:234
> > in eval(::Any) at ./boot.jl:233
> >
> >
> >
> > Does Julia provide a way to use such macros stored in variables? Thanks!
>
