Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!uunet!mcsun!ukc!edcastle!aiai!jeff
From: jeff@aiai.ed.ac.uk (Jeff Dalton)
Newsgroups: comp.lang.scheme
Subject: Re: Why macros impair readability
Message-ID: <4291@skye.ed.ac.uk>
Date: 9 Mar 91 21:49:19 GMT
References: <9103071300.aa28959@mc.lcs.mit.edu>
Reply-To: jeff@aiai.UUCP (Jeff Dalton)
Organization: AIAI, University of Edinburgh, Scotland
Lines: 36

In article <9103071300.aa28959@mc.lcs.mit.edu> lyn@altdorf.ai.mit.EDU (Franklyn Turbak) writes:

>I agree wholeheartedly; my definition of "readability" *is* weak and not
>very useful.  However, it's the only one I could think of at the time
>of writing that allowed me to raise the set of points I wanted to raise:
>that macros complicate reasoning about order of evaluation, static scope, 
>first-classness, and debugging. 

There was a much easier solution, namely to raise those points
without trying to tie them to the definition of readability.

>I'd rather have a much stronger notion of readability that more people
>find in tune with their intuitions.  From the discussions so far,
>there's a lot of people who *do* feel that macros can make programs
>hard to read.  My goal is to understand better *why* they feel this
>way.  

I'd agree with that.

But one reason is that macros are often written as fairly complex list
structure manipulations.  Backquote helps some, extend-syntax much more.
There are a number of simple reasons like this, that don't require a
deep analysis.

>I am working on an improved model of "readability" to better handle
>your objection.  The basic idea is that macros are harder than
>procedures for the reader to model behaviorally because of the various
>funky things that can be done in complex desugarings. 

N.B. _can_ be done.  The complaints ought to be about the funky
things. 

Note too that a desugaring can be complex without the macro being hard
to understand if it implements a well-defined, easy to manage abstraction.
For example, I can understand list comprehensons in Haskell more
easily than I can understand the desugaring.