Bug in 'as' processing in pattern matching? 3.0.4 and 3.0.6 #8024

vicuna · 2003-02-21T17:54:11Z

Original bug ID: 1552
Reporter: administrator
Status: closed
Resolution: not a bug
Priority: normal
Severity: minor
Category: ~DO NOT USE (was: OCaml general)

Bug description

Hello, I was using 'as' patterns and found behavior that seemed strange.

--
let ((a,b) as x ,(c,d) as y) as z = ((1,2),(3,4))
in
((a,b,c,d),(x,y,z));;

I'd expect x == (a,b) and y == (c,d), but I don't get that, I get
y == ((a,b),(c,d))

Invoke this and see what I mean:

let ((a,b) as x ,(c,d) as y) as z = ((1,2),(3,4))
in
y;;

: (int * int) * (int * int) = (1, 2), (3, 4)
--

Shouldn't it give me (3,4)?

However, if I insert an extra set of paremthesis, it works:

let ((a,b) as x ,((c,d) as y)) as z = ((1,2),(3,4))
in
y;;

: int * int = 3, 4
--

So is this a bug?

Scott

vicuna · 2003-02-23T13:41:29Z

Comment author: administrator

On Sun, 23 Feb 2003 15:29:14 +0100 (MET), Damien Doligez caml-bugs@pauillac.inria.fr writes:

Hello, I was using 'as' patterns and found behavior that seemed strange.

The answer to your question is found a bit further in your own mail...

Is SML-NJ the same? I don't remember it behaving the same way but
haven't used it in a while.

However, if I insert an extra set of paremthesis, it works:

So this is only a question of precedence. The "as" keyword has the lowest
precedence, so it binds everything to its left, unless you use parentheses.

Ah, I see. I had not realized that ',' is just another binary infix
operator. Now I see and understand. Thanks!

Scott

vicuna · 2003-02-23T14:29:15Z

Comment author: administrator

Hello, I was using 'as' patterns and found behavior that seemed strange.

The answer to your question is found a bit further in your own mail...

However, if I insert an extra set of paremthesis, it works:

So this is only a question of precedence. The "as" keyword has the lowest
precedence, so it binds everything to its left, unless you use parentheses.

So is this a bug?

No, since it is properly documented. The worst you can call it is "an
unfortunate design decision".

-- Damien

vicuna closed this as completed Feb 23, 2003

vicuna added the bug label Mar 19, 2019

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Bug in 'as' processing in pattern matching? 3.0.4 and 3.0.6 #8024

Bug in 'as' processing in pattern matching? 3.0.4 and 3.0.6 #8024

vicuna commented Feb 21, 2003

vicuna commented Feb 23, 2003

vicuna commented Feb 23, 2003

Bug in 'as' processing in pattern matching? 3.0.4 and 3.0.6 #8024

Bug in 'as' processing in pattern matching? 3.0.4 and 3.0.6 #8024

Comments

vicuna commented Feb 21, 2003

Bug description

-- let ((a,b) as x ,(c,d) as y) as z = ((1,2),(3,4)) in ((a,b,c,d),(x,y,z));;

Invoke this and see what I mean:

However, if I insert an extra set of paremthesis, it works:

vicuna commented Feb 23, 2003

vicuna commented Feb 23, 2003

--
let ((a,b) as x ,(c,d) as y) as z = ((1,2),(3,4))
in
((a,b,c,d),(x,y,z));;