Path: utzoo!attcan!uunet!mcsun!hp4nl!eurtrx!euraiv1!reino
From: reino@cs.eur.nl (Reino de Boer)
Newsgroups: comp.software-eng
Subject: Re: Theory vs. Practice in CS Education
Message-ID: <1989Nov21.141820.5263@cs.eur.nl>
Date: 21 Nov 89 14:18:20 GMT
References: <4967@ae.sei.cmu.edu> <1989Nov17.090716.11068@cs.eur.nl> <4994@ae.sei.cmu.edu>
Organization: Erasmus Universiteit Rotterdam, dept. CS (Informatica)
Lines: 40

rsd@sei.cmu.edu (Richard S D'Ippolito) writes:

>In article <1989Nov17.090716.11068@cs.eur.nl> Reino de Boer writes:


>-Although a compiler course is relevant to software engineers, if only to
>-understand more about designing languages and their implementation.
>-Didn't someone once say:
>-	each program is in fact an interpreter for a language (where the
>-	language defines all legal input to the program, and the semantics
>-	of the various inputs)
>-If noone ever said it, how about your comments ?

>I'm sorry -- If this is directed to me, I am unable to answer you as I do
>not understand the point you are trying to make.

The point I'm trying to make is maybe best given in a simple example:

Suppose we need a program to take the sum of 5 numbers, where these 5
numbers are the only input to the program. Futhermore, let's assume we
want each input number to be positive and less than 1000.
Each number will be entered on a line by itself.

The program we will write can be viewed as an interpreter for a language
with the following syntax:
<input> ::= <numeral> <numeral> <numeral> <numeral> <numeral>
<numeral> ::= <digit> [ <digit> [ <digit> ] ] <nl> | 0 <nl>
<digit> ::= 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
<nl> ::= the representation of the terminating newline.

The (informal) semantics can then be described as follows:
The output of the interpreter consists of the sum of 
the numbers resulting from conversion of the numerals.

Hope this explains -- reino

-- 
Reino R. A. de Boer
Erasmus University Rotterdam ( Informatica )
e-mail: reino@cs.eur.nl