You could do
tmp = one(eltype(z))
@nexprs $N j->(tmp *= z[r, i_j])
out[r,ix] = tmp
Does that do what you want?
Alternatively, build up the expression outside the quote block:
args = [:(z[r, $i]) for i = 1:N]
ex = Expr(:call, :*, args...)
and then use $ex where your former @nexprs is.
--Tim
On Thursday, May 07, 2015 09:03:08 AM Spencer Lyon wrote:
> Consider the following expression:
>
> julia> macroexpand(:(@nexprs 3 j->(out[r, ix] *= z[r, i_{3-j+1}]) ))
> quote
> out[r,ix] *= z[r,i_3]
> out[r,ix] *= z[r,i_2]
> out[r,ix] *= z[r,i_1]
> end
>
>
> What I would really like to be able to do is have a macro generate the
> expression
>
> julia> ... some magic incantation here
> quote
> out[r,ix] = z[r,i_3]*z[r,i_2]*z[r,i_3]
> end
>
>
> Does anyone see an easy way to do this?
>
> For some context, this appears in the following block of code:
>
> immutable Degree{N} end
>
> function n_complete(n::Int, D::Int)
> out = 1
> for d=1:D
> tmp = 1
> for j=0:d-1
> tmp *= (n+j)
> end
> out += div(tmp, factorial(d))
> end
> out
> end
>
> @generated function complete_polynomial!{N}(z::Matrix, d::Degree{N},
> out::Matrix)
> complete_polynomial_impl!(z, d, out)
> end
>
> function complete_polynomial_impl!{T,N}(z::Type{Matrix{T}},
>
> ::Type{Degree{N}},
> ::
> ::Type{Matrix{T}})
>
> quote
> nobs, nvar = size(z, 1), size(z, 2)
> if size(out) != (nobs, n_complete(nvar, $N))
> error("z, out not compatible")
> end
> out[:, 1] = 1.0
> out[:, 2:nvar+1] = z
>
> # reset first column to ones
> @inbounds for i=1nobs
> out[i, 1] = 1.0
> end
>
> # set next nvar columns to input matrix
> @inbounds for n=2:nvar+1, i=1:nobs
> out[i, n] = z[i, n-1]
> end
>
> # reset all trailing columns to 1s
> @inbounds for n=nvar+2:size(out, 2), i=1:nobs
> out[i, n] = 1.0
> end
>
> ix = nvar+1
> @nloops($N, # number of loops
> i, # counter
> d->((d == $N ? 1 : i_{d+1}) : nvar), # ranges
> d->(d == $N ? nothing :
> (ix += 1 ; for r=1:nobs @nexprs $N-d+1 j->(out[r, ix]
> *= z[r, i_{$N-j+1}]) end)),
> Expr(:block, :nothing) # bodyexpr
> )
> out
> end
> end
>
> I would like to be able to generate the expression I mentioned before for
> two reasons: 1.) so I can avoid having to set all trailing columns to 1s
> before the @nloops and 2.) so I can only traverse out once in the prexpr
> part of the @nloops call.
>
> Any suggestions would be most welcome. Thanks!
