Proposal for @decimal macro

[michikawa07]

Would the following macros be useful?

julia> macro decimal(ex)
           trans!(e::Real) = :(Decimal($e))
           trans!(e::Expr) = begin
               for (i,a) in enumerate(e.args)
                   a isa Integer && continue
                   a isa Real && (e.args[i] = Decimal(a))
                   a isa Expr && trans!(a)
               end
               ex
           end
           :(number($(trans!(ex))))
       end
@decimal (macro with 1 method)

julia> 100 * 1.1576  
115.75999999999999                                                                                                                                                                                                          

julia> @decimal 100 * 1.1576
115.76  

[michikawa07]

This implementation is very rough, but it works well enough to explain my concept.
That is, I expect the expression to be decimalized simply by prefixing it with @decimal.

[barucden]

What is the motivation? Why is this:

@decimal 100 * 1.1567

better than this:

Decimal(100) * 1.1567

?

[michikawa07]

I think ... @decimal is more simple.
This is because, if the expression become more complex;
in the case of @decimal, we just add a macro at the front,
in the case of Decimal constructor, we must add everywhere it is needed.

[barucden]

I think this is a very rare use case to justify adding a macro to the library. Operations promote, so when computing, e.g., x + y, you only need to convert x to a Decimal and y will be promoted automatically.

Unless the demand for this feature grows (this issue has been here for almost a year and attracted no users), I don't think we should add this.