Re: [Caml-list] a question about syntax

[Kenneth Adam Miller <kennethadammiller@gmail.com>]

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No, it's keywords "in" that assigns the terminus to the current phrase so
to speak.

The first would look like this, if I understand you correctly:

let f x = { field1 = match x with _ -> true | field2 = 2} in

But there are several problems with the above statement. First, you used a
semicolon in place of a |, and a | expresses to the match statement what
the various cases are. As in,

match x with | case1 ... | case 2 | ...

Second, alternatively to that interpretation, you might want it to be that
you match within the assignment like this:

let f x = { field1 = (match x with ... ); field2 = ... } in

A problem is that you used match x with _ -> true | field2, but the _ is
the catchall keyword, so field2 is never going to get hit. What you've
expressed in the second let statement is equivalent to this:

let f1 = match x with _ -> true in
let f x = { field1 = f1; field2.... }

On Tue, Feb 13, 2018 at 10:31 PM, Tim Leonard <Tim@timleonard.us> wrote:

> A simple question of syntax: why does the first definition of function f
> cause a syntax error?
> Shouldn’t the semicolon syntactically terminate the match expression?
>
> type my_record = { field1 : bool; field2 : int };;
>
> let f x = { field1 =   match x with _ -> true  ; field2 = 2 };; (* this
> fails *)
>
> let f x = { field1 = ( match x with _ -> true ); field2 = 2 };; (* this is
> ok *)
>
>
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