On Tue, Feb 13, 2018 at 10:31 PM, Tim Leonard <Tim@timleonard.us> wrote:
[...]
type my_record = { field1 : bool; field2 : int };;
let f x = { field1 = match x with _ -> true ; field2 = 2 };; (* this fails *)
This fails because OCaml overloads ';' in a few different ways, significantly: (1) as a field separator in a record, and (2) as a sequencing operator between two expressions. In case of ambiguity OCaml parses as the latter, but you really meant the former.
(2) 'sequencing operator' means that something like:
let x = print_endline "Hi!"; 1
... will evaluate whatever is on the left of the ';', throw away its value (in this case 'unit'), then evaluate whatever is on the right of the ';' and return its value as the final value of the compound expression.