A polynomial from a string

[sumiya11]

Hi. Is it possible to construct a polynomial from a string? Like this:

using Nemo
R, _ = QQ["x","y"]
R("x + y")

If possible, I would like to avoid eval, which is discussed in #781, because I have observed it to be quite slow.

[thofma]

Some time ago I added code in Oscar for doing this: https://github.com/oscar-system/Oscar.jl/blob/c0fadd1a7ff95ba76841972ba5ca5122f5a5aba0/experimental/FTheoryTools/src/auxiliary.jl#L389-L436

We could probably move it here. In the meantime, just steal it.

[sumiya11]

Thank you for the suggestion. I will use it at the moment.

However, let me mention: this approach with Meta.parse + custom_eval had not worked in the past for larger polynomials (say 100 MB). It either never finished or Meta.parse errored. So in the past I wrote my own parsers for polynomials to replace Meta.parse, in addition to custom_eval. Therefore, I think it could be a useful feature to provide a faster parser for polynomials out of the box in Nemo.

[thofma]

Ah yes, I remember the julia parser is really bad at this. I think this is very low priority for the main developers, but any contribution in this regard of course welcome.