Re: [CZT-Users] Logical operator ambiguity considered harmful

[Rob A. <rd...@le...>]

Ian,

Thanks - I was having a brainstorm. I note one oddity with the precedences. If you work at it, both ways of putting the brackets in something of the form %mu x: X | A /\ B can be type correct. The precedences give you the predicate conjunction (%mu x : X | A) /\ B, whereas I would have expected %mu x : X | (A /\ B). As Phil Clayton said on another forum, any reasonable Z style guide would strongly encourage people to bracket these weird cases. In retrospect, I wish the standard had been more restrictive about brackets. Having worked a lot with a large multi-author Z spec over the last few years, misplaced brackets are one of the most common causes of error.

Regards,

Rob.

On 19 Jul 2011, at 11:02, Ian Toyn wrote:

> Rob Arthan writes about parsing the following predicate.
> 
> {} = %lambda x: %Z @ [y: %Z | x < y] \/ [y:%Z  | y < x]
> 
> ISO Z assigns precedences to operators.
> Function construction binds tighter than relation operator application,
> which binds tighter than disjunction (whether predicate or expression).
> Those precedences have the effect of requiring the parse indicated below by parentheses.
> 
> ({} = (%lambda x: %Z @ [y: %Z | x < y])) \/ [y:%Z  | y < x]
> 
> Only then is any ambiguity in the use of logical operations considered.
> Since the left disjunct is a predicate, this disjunction is a predicate.
> 
> CZT (and also CADiZ) find the parse described above.
> 
> Does that work-around the issue, or did I miss something?
> 
> Regards,
> Ian
> 
> 
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