Macro design recommendations for `do-end` like semantics

General Usage
1

In Julia, there’s a function do block syntax like so:

foo() do x
  println(x)
end

where foo is defined like foo(f::Function)

I’m interested in writing a macro that affects a block. i.e. I want user facing code to look something like this:

foo() do x
  println(x)
end

but where foo is defined like this instead: foo(expr::Expr)

I’ve tried writing a macro but this following example doesn’t work (because @foo() is evaluated first):

julia> @foo() function(x)
  println(x)
end

ERROR: syntax: extra token "function" after end of expression
Stacktrace:
 [1] top-level scope
   @ none:1

And this would work but it is easy for users to accidentally remove the space between @foo and () and that leads to the previous structure which throws an error.

@foo () function(x)
  println(x)
end

I’m curious if anyone has suggestions for alternative designs here?

2

It’s not so clear to me what you want, but macros can certainly take do blocks:

julia> macro foo(exs...)
         @show exs; nothing
       end;

julia> @foo(y, 2, z=3) do x
         g(x)
       end
exs = (:((x,)->begin
          #= REPL[138]:2 =#
          g(x)
      end), :y, 2, :(z = 3))
3 Likes
3

Ah nice! I thought I tried this but must have messed up the number of arguments and failed to see the dispatch error. That helps! Thanks!!