[ferret_users] referencing to datasets relative to current

[Marco van Hulten <marco.van-hulten@xxxxxxxxxxxx>]

Hello,

I have 2*N datasets loaded, N of the sort that contain variable A, and
N sets that contain B.  I want to combine these in certain variable
definitions,  like:

    let N = 5
    let myvar = A[d=1] + B[d=`N+1`]
     !-> DEFINE VARIABLE myvar = A[d=1] + B[d=6]
or
    set data 1
    let myvar = A + B[d=`N+1`]
     !-> DEFINE VARIABLE myvar = A + B[d=6]

My script always sets the data set to any of {1..N}, so it doesn't have
to be 1.  I can get the dataset number with the dsetnum return value
of A, but as the backtics below are immediately evaluated, the
definition is not updated after changing datasets:

    set data 1
    let dset_num = `A,return=dsetnum`
    let myvar = A + B[d=`N+dset_num`]
    sh var myvar
     MYVAR = A + B[D=6]
    set data 5
    sh var myvar
     MYVAR = A + B[D=6]

However, I want to to get the result

     MYVAR = A + B[D=10]

while not redefining dset_num.  I could make dset_num a symbol, so
that it is evaluated later on, but that results in embedded backtic
problems.

Is it at all possible what I want?

Marco

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