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
