Re: [Caml-list] a question about syntax

[Oliver Bandel <oliver@first.in-berlin.de>]

Zitat von Tim Leonard <Tim@timleonard.us> (Tue, 13 Feb 2018 22:31:14 -0500)

> 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?

No.
You can use semicolon to put more then one expression together.
So the "field2 = 2" is seen as part of the match.

If you have a pattern matching, this way you can put multiple  
commands/expressions in a row,
without the need to use begin/end or ( ) in any match-case.
It's the other way around: you need to put begin/end or ( ) around a  
match-statement.

This way you have to add one such enclosing around a match-statement,
instead of one such enclosing in any match-case of such a statement.


>
> type my_record = { field1 : bool; field2 : int };;
>
> let f x = { field1 =   match x with _ -> true  ; field2 = 2 };; (*  
> this fails *)

Here I get "Error: Unbound value field2",
which is, because the match-case reaches until the }.



>
> let f x = { field1 = ( match x with _ -> true ); field2 = 2 };; (*  
> this is ok *)

Here it works, because the match-statement is sorrounded / enclosed by  
( and ).

Ciao,
   Oliver