Handle objects of type Symbol and Expr (Matching Julia expressions)

[gafter]

See also RelationalAI-oss/Rematch.jl#19

julia> @match :(5+5) begin
         :($_ + $_) => true
         _ => false
       end

This should print true

Slightly more generally, the pattern

• :(a + b) should match the expression :(a + b) and nothing else
• :($_ + $_) should match any binary addition
• :($a + $b) should match any binary addition, and define the pattern variables a and b.
• :($$a + $$b) should match an addition, where the left-hand-side corresponds to the value of the local variable a and the right-hand-side corresponds to the value of the local variable b. One $ is for escaping from the enclosing :, and the other is for escaping the pattern syntax.

See also JuliaServices/Rematch2.jl#6