From: Vladimir Konrad <v.konrad@...>
Date: 2007-01-30T06:20:48+09:00
Subject: Re: Working with the parse tree in Ruby?

> Martin, in addition to what Aaron has written, I'd like to ask you what
> you need this for. I've been playing with implementing macros in Ruby a
> few times, but I found no compelling reason to support them in Ruby.

well, i have a use case (but this is doable, i think, with existing ruby 
using code generation and eval).

i wanted to write a "universal netcdf dump" procedure for netcdf files 
(the netcdf library for ruby exists). the format i have has few 
dimensions and one multi-dimensional array. the problem is that the 
number of dimensions can vary - e.g. you can have value(dim1) or 
value(dim1,dim2,dim3...).

what i wanted was a general way to dump the multidimensional variable 
value + each related value in each dimension as a table for import to 
SQL. this translates to nested iterators (where number of iterators is 
the number of dimensions) e.g for 2 dimensions something like:

# this is pseudo code, dim1, dim2, value are arrays from netcdf

dim1[].length.times{|dim1_i|
  dim2[].length.times{|dim2_i|
    print dim1[dim1_i], dim2[dim2_i], value[dim1_i,dim2_i]
}}

i could not imagine to do this without a macro (or without code 
generation and eval).

vlad

ps: i have not done the "universal netcdf dump" procedure as i do not 
really need it for the import but it was an interesting thing to think 
about .

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