The reduced case is:
h((x1::Int64,x2::Int64)...) = x1+1
Which doesn't work, because the "..." conflicts with the vararg syntax (the
error message is admittedly not very good).
I would suggest to generate the entire function from your macro, in which
case you can just splice the tuple in and everything should work.
ps: using eval inside a macro, and parsing concatenated strings like that,
can and should be avoided. Build Expr objects instead.
On Thu, Apr 30, 2015 at 5:19 PM, David Gold <david.gol...@gmail.com> wrote:
> I'm working (in 3.7) on a function that takes two functions f and g as
> inputs, merges all non-conflicting methods of f and g into one function h,
> and returns h. I'm trying to use macros to generate the signatures of each
> method for h:
>
> macro argsgen(typle, n::Int64)
> y = eval(:($typle))
> xn = symbol("x$n")
> return :( $xn :: $(y[n]) )
> end
>
> macro repper(typle, n::Int64)
> ex = "@argsgen($typle, 1)"
> for i in 2:n
> ex = string(ex, ", @argsgen($typle, $n)")
> end
>
> return parse(ex)
> end
>
> So, if f has a method with signature (x::Int64), then I can feed the
> 1-tuple '(Int64,)' to @argsgen, which generates the proper signature:
>
> julia> ex1 = macroexpand( :(@argsgen((Int64,), 1) ))
> :(x1::Int64)
>
> and I can thereby define a method for h:
>
>
> julia> h(@argsgen((Int64,), 1)) = x1 + 1
> foobar (generic function with 1 method)
>
> julia> h(1)
> 2
>
> The problem is when I try to do this for a signature of more than one
> argument, say (Int64, Int64). Above I've tried implementing a macro that
> generates an expression of repeated '@argsgen' calls with the appropriate
> second argument:
>
> ex = macroexpand( :( @repper (Int64, Int64) 2 ) )
> :((x1::Int64,x2::Int64))
>
> which doesn't quite work when I attempt to use it for a signature:
>
> julia> h(@repper (Int64, Int64) 2) = x1 + x2
> ERROR: syntax: "(x1::Int64,x2::Int64)" is not a valid function argument
> name
>
> How can I get @repper to return an expression that isn't a tuple, but also
> has two @argsgen calls separated by a comma? I've tried a couple of other
> ways of doing this, but each expression wants to be returned as a tuple.
> And I can't find out how to make the tuple splat in such a way that works
> as a signature for h. Any thoughts? (Also, I imagine the tupocalypse will
> break this, but I can deal with that later.)
>
> Thank you all!
> David
>
