Honestly, I just need a cheat sheet for how to read the symbols using english words. I understand the concepts of the logical application of typing, but I don't read computer science dissertations regularly enough to make them the mapping of symbols to meaning stick.
> Honestly, I just need a cheat sheet for how to read the symbols using english words.
Amen… however I believe the existence of such a cheat sheet would represent an existential economic risk for PLT researchers, and they’d be incentivized to add more Greek (and, eventually, Cyrillic, then Czech, then eventually Xhosa and probably Klingon) symbols in order to retain access to funding. It’s only a matter of time before someone reinvents the paper town inside of PLT papers, if they haven’t already.*
* the above is meant to be taken facetiously
> I understand the concepts of the logical application of typing, but I don't read computer science dissertations regularly enough to make them the mapping of symbols to meaning stick.
I just wish CS (and, indeed, mathematics) was even remotely internally consistent… cross the boundaries between any two extremely narrow domains and ω can mean anything. It’s (very) vaguely consistent within PLT, but even there getting lowercase omega “stuck” in your head as having one English translation is just a pathway to pain.
I read `A |- x : t` as "In context A, x has type t". An entire inference rule (i.e. the horizontal bar separating some premises from a conclusion) is read as as "if P, Q, ... hold, then R holds"; or, sometimes, "We obtain R if we have P, Q, ...".
That works if typing rules are unambiguous. But you might have |- x : t1, as well as |- x :t2 (for example, numeric literals in Haskell can have several types).
Instead of saying "x has type t", one could think of it as "x can be inferred to be of type t" or "we can derive/prove that x has type t". The latter mirrors the usage in formal logic where the turnstyle symbol generally is used to mean "is provable".
This is all true, although nothing about the reading "x has type t" implies that "x" can only have one type. It is a separate metatheorem about your system of inference rules that terms have unique types -- and not even one that is always true, e.g. in the presence of subtyping.
> for example, numeric literals in Haskell can have several types
Technically, numeric literals in Haskell have precisely one type: `(Num a) => a`. The literal `42` is actually interpreted as the expression `fromInteger (42 :: Integer)`, where `fromInteger` is a function on the `Num` typeclass. In turn, the `Num` typeclass constraint desugars to a function taking a dictionary of functions, `NumDict a -> a`. The typeclass machinery just means GHC will infer the appropriate instance whose dictionary should be provided.
(technically technically, GHC can be even cleverer if it knows statically which dictionary will be used, avoiding using the dictionary entirely; but this desugaring to dictionaries is ground truth, semantically.)