Mirrors iteration 101's parse-fun change inside parse-let's
parse-one!:
- same '(IDENT, ...)' detection on collect-params
- same __pat_N synth name for the function param
- same innermost-first match-wrapping
Difference: for inner-let the wrapping is applied to the rhs of the
let-binding (which is the function value), not directly to a fun
body.
let f (a, b) = a + b in f (3, 7) = 10
let g x (a, b) = x + a + b in g 1 (2, 3) = 6
let h (a, b) (c, d) = a * b + c * d
in h (1, 2) (3, 4) = 14