pattern matching

[danilopedraza]

To start, I won't add a match-like expression, but to write patterns in let expressions. Something like this:

let fib(0) := 0
let fib(1) := 1
let fib(n) := fib(n - 1) + fib(n - 2)

[danilopedraza]

To set a start for PM, I will set some requirements:

• [x] Match constants
• [x] Match anything with the wildcard _
• [x] Match lists and prefixes (i.e. [first|most])
• [x] Check for equality using the same symbol in different places (f(a,_,a) matches f(1,0,1) but not f(1,2,3))

[danilopedraza]

This is naively implemented and decently tested now.