Pattern matching for expressions

[albop]

For the preliminary implementation, a pattern is an expression, with some wildcards.
Wildcards are valid identifiers starting by one underscore.

For instance, _a + _b*_a is supposed to match p + b*p but not p + b*c.

We can use that to define the elements of syntax that we want, for instance to define _x[_inds](_t) as the generic form of a timed and index variable (like v_{i,t+1})

There is a crude python implementation in https://github.com/EconForge/dolang/blob/master/dolang/pattern.py.

Some questions:

• are there available libraries which do it efficiently ?
• we probably want to "type" the wildcard so that, in the above example, _t could stand for a signed integer and _inds would be expected to be a list of indices
• would we be better of by defining the expression parser ourselve instead of operating on the syntax tree ?

[sglyon]

Cool idea. I like it.

On the Julia side we have the @match macro in MacroTools.jl