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From: ken@aiai.ed.ac.uk (Ken Johnson)
Newsgroups: comp.edu
Subject: Re: Which language to teach first?
Message-ID: <670@skye.ed.ac.uk>
Date: 3 Aug 89 10:28:48 GMT
References: <3876@shlump.nac.dec.com> <5407@ficc.uu.net>
Reply-To: ken@aiai.UUCP (Ken Johnson)
Organization: AIAI, University of Edinburgh, Scotland
Lines: 40

In article <5407@ficc.uu.net> peter@ficc.uu.net (Peter da Silva) writes:

>Some people swear by LOGO or some other very high level language. I think
>a wide variety of such languages should be presented to students, but
>only after they're familiar with conventional data and control structures.

I think this depends on what you are training the students to do.  There
is nothing you can do with conventional control structures that you
can't do with recursion: for example, printing numbers from 1 to N can
be done with

  to print_them :n
    if :n = 0 [stop]
    print_them :n - 1
    print :n
  end

On the other hand if you really want a WHILE statement you could
define

  to while :condition :command
    if run :condition [run :command while :condition :command]
  end

and then use that definition in a procedure:

  to print_them :n
    local "i
    make "i 1
    while [:i <= :n] [print :i make "i :i + 1]
  end

I happen to think the first print_them has a grace and beauty that the
looping version lacks, but that's my taste. 

-- 
Ken Johnson, AI Applications Institute, 80 South Bridge, Edinburgh EH1 1HN
E-mail ken@aiai.ed.ac.uk, phone 031-225 4464 extension 212
`I have read your article, Mr.  Johnson, and I am no wiser than when I
started.' -- `Possibly not, sir, but far better informed.'