match expressions

[lutzhamel]

Add match expressions a la Rust to Asteroid,

let p = (1,2).
let x = (match p
   with (x,y) if x > y do
      "GT"
   with (x,y) if x < y do
      "LT"
   with _ do
      throw Error("not a valid tuple"))
assert(x =="LT").

Since it is an expression it does not have an end keyword, the end keyword would look really weird in expressions, but therefore this expression is syntactically very ambiguous similarly to lambda functions and needs to be surrounded by parens in most cases.

[lutzhamel]

Match statements a la Python are much more amenable to our syntax

let p = (1,2).
match p
   with (x,y) if x > y do
      let x = "GT".
   with (x,y) if x < y do
      let x = "LT".
   with _ do
      throw Error("not a valid tuple").
end
assert(x =="LT").

So, we'll probably go with those.