Re: question about Exercise 5.3.7

From: Assaf Kfoury (kfoury@cs.bu.edu)
Date: Fri Sep 24 2004 - 19:35:13 EDT


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Date: Fri, 24 Sep 2004 19:35:13 -0400
From: Assaf Kfoury <kfoury@cs.bu.edu>
Organization: Boston University
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To: Quan <Yuan@cs.bu.edu>, cs520@cs.bu.edu
Subject: Re: question about Exercise 5.3.7
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You are referring to a syntactic error, not an evaluation error. A
expression of the form "if true then" is not a legal term, and neither
are expressions of the form "if true", or "then false", or "else true",
etc., all of which should be caught by a syntactic analysis, before they
are evaluated.

The special value "wrong" is introduced to handle differently semantic
(or evaluation) errors.

Assaf

Quan wrote:

>Prof. Kfoury,
> In the Exercise 3.5.16, I am not clear how it handles error like "if true then". When the "if_then_else" statement is not complete, it seems no rules can apply.
> Thanks,
>
>Quan
>
>
>



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