macro capture about mlstyle.jl

[thautwarm]

@Roger-luo Would this be sufficient?

https://thautwarm.github.io/MLStyle.jl/latest/tutorials/capture/

[thautwarm]

like this?

@capture ex begin
    f($x, y) => x  # AST pattern
   $(Expr(:meta, a)) => a # Expr pattern
end

Does it really make sense for we already have the following?

@match ex begin
  :(f($x, y)) => x
   Expr(:meta, a) => a
end

It seems that @capture just simplify AST pattern a little.

[Roger-luo]

Umm, it is just an eye candy of @match in MLStyle, and has similar interface of regex, e.g

@capture <template> <expr>

@capture :(1 + $x + $y) 1 + a + b

this will return a tuple: (:a, :b)

[thautwarm]

The problem is $ inside a Quote would be evaluated eagerly if it's not an argument of macrocall, so if you want to use such a @capture macro, you cannot share a common template with multiple callsites.

template = :(1 + $a + $b) # wrong! a, b would inserted here

So you cannt do these:

@capture $template ex1
@capture $template ex2

If we quote an Expr twice :(:($a)), the $ would then be preserved.