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From: S.Clayman@cs.ucl.ac.uk
Newsgroups: comp.lang.functional
Subject: Re: concrete syntax (was: "off-side rule")
Message-ID: <1386@ucl-cs.uucp>
Date: 25 Jan 91 17:07:43 GMT
Sender: news@cs.ucl.ac.uk
Lines: 44


I have just read about 20 messages concerning off-side rules,
white space having meaning etc...

Firstly I would like to know how many of the people doing
the criticism have actually USED a language with off-side rules.

Secondly, languages aren't necessarily designed so that the compiler
writer's task is made easier.  Progamming language design should
consider the users of the language; ease of expressing abstract ideas
should be more important than how many minutes Eric Compiler-Writer
saved when doing the parser.

The most important thing I want to say is I have NEVER had a problem
with off-side rules and white space introducing bugs, but I have
introduced bugs in C programs by having single statements and then
adding another statement at the same indentation thinking thaey are
the same block of code. Having both lines indented to the same place
has caused the confusion.

I have just written a 2000 line Miranda program and off-side and white
space aided me in the expression of my ideas, helped avoid silly
errors, and made writing bug free code easier.

Indentation is used for local definitions; if the compiler complained
about things being off-side I went straight to them, and easily saw
what the problems were.

Also, i have been teaching students Miranda, they easily grasp the
concept of left hand-sides and right hand-sides of expressions
with local definitions to the right of the =.
These are 1st years, some of whom have never seen a computer before.
They can write working programs within a day, and have done complex
projects after 1 term (e.g. text formatters, symbolic differentiators,
stock control systems)
They are now learning C; whose layout and syntax is not so easily
learnt, and has a large syntactic overhead for the expressivness.
I cant imagine any of the writing similar projects after 1 term of C.

I would like to add that the Haskell approach of a formal translation
to a form with no off-side is a good idea, someone somewhere
is to be commended for that.

stuart