strategize about implementation for Type::TRelated

[mhuesch]

try to figure out what a good structure might look like.

relates to #6.

[mhuesch]

potential route 1

pub enum Type {
    TVar(TV),
    TCon(String),
    TList(Box<Type>),
    TRelated(RelatedOp, Box<Type>, Box<Type>),
}

pub enum RelatedOp {
    RArr,
    RPair,
    RDiv,
    RMul,
}

this adding this as a constructor to Type would allow us to combine types together.

this is perhaps overreaching, but we could refactor/normalize the constructors of TArr and TPair away into the (binary operation) TRelated, but adding them as constructors to RelatedOp. I included that above, just as a sketch.

anyways, back on topic

RDiv and RMul would represent the "multiplication" of two other types. it's possible this is too powerful: we would be able to have stuff like List Int * List (Bool -> Bool) - what would that really mean? a list of integers multiplied by a list of bool to bool functions...

we could also express more sensible things like "meters * seconds", this way.

potential route 2

it's possible we want to only allow TRelated inside of TCon.

that way we can restrict what pieces can get combined together. however we might want TV s inside of our TRelated, to have polymorphism?

so we could say a / sec where a might be Likes, or Claps, or meters...