That's quite a lot cleaner than what I came up with, and keeps as much of
the expression as possible in regular code-syntax. Thanks!
// T
On Tuesday, September 22, 2015 at 11:23:33 AM UTC+2, Tim Holy wrote:
>
> What you're trying isn't easy because the results of @ntuple, unless
> contained
> inside an Expr, will be eval'ed so you'll still create the tuple. And
> expression-tuples are not iterable, so you can't splat them.
>
> Manual construction:
>
> function foo(N)
> args = [symbol("xs_",k) for k = 1:N]
> :(gradient(A, $(args...)))
> end
>
> The Cartesian package had an `@ncall`, but I found that I so often wanted
> new
> combinations of arguments that it wasn't worth it so didn't port it over
> to
> Base.
>
> --Tim
>
> On Tuesday, September 22, 2015 12:11:05 AM Tomas Lycken wrote:
> > I’m having real difficulties grok-ing macro hygiene. I’ve read the
> manual
> > entry, but didn’t get much wiser, so I’m hoping the solution to my
> current
> > problem will be another data point I can use to understand (and I need
> this
> > to work :P).
> >
> > I have a utility function that builds an expression (which will later be
> > interpolated into the method body of a generated function, but that’s
> out
> > of scope for my current problem), something like this:
> >
> > julia> using Base.Cartesian
> >
> > julia> foo(N) = :(gradient(A, (@ntuple $N k->xs_k)...))
> > foo (generic function with 1 method)
> >
> > julia> macroexpand(foo(2))
> >
> > :(gradient(A,(xs_1,xs_2)...))
> >
> > Now, as you see, the generated tuple is splatted at run time. I’d like
> to
> > try to move that splatting to compile time, so that the generated
> > expression is rather :(gradient(A, xs_1, xs_2)). I’ve tried variants on
> the
> > following, but as you can see I haven’t had any success.
> >
> > I assume that I need to escape N somehow - but how?
> >
> > julia> foo(N) = :(gradient(A, $((@ntuple N k->xs_k)...)))
> > ERROR: MethodError: `_ntuple` has no method matching _ntuple(::Symbol,
> > ::Expr)
> >
> > julia> foo(N) = :(gradient(A, $((@ntuple $N k->xs_k)...)))
> > ERROR: MethodError: `_ntuple` has no method matching _ntuple(::Expr,
> ::Expr)
> >
> > julia> foo(N) = :(gradient(A, $(esc((@ntuple N k->xs_k)...))))
> > ERROR: MethodError: `_ntuple` has no method matching _ntuple(::Symbol,
> > ::Expr)
> >
> > julia> foo(N) = :(gradient(A, $(esc((@ntuple :N k->xs_k)...))))
> > ERROR: MethodError: `_ntuple` has no method matching _ntuple(::Expr,
> ::Expr)
> >
> > julia> foo(N) = :(gradient(A, $(@ntuple esc(N) k->xs_k)...))
> > ERROR: MethodError: `_ntuple` has no method matching _ntuple(::Expr,
> ::Expr)
> >
> > julia> foo(N) = :(gradient(A, $(@ntuple esc(:N) k->xs_k)...))
> > ERROR: MethodError: `_ntuple` has no method matching _ntuple(::Expr,
> ::Expr)
> >
> >
>
>
