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Re: return

From: Stefan Monnier
Subject: Re: return
Date: Fri, 26 Nov 2010 09:59:51 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux)

> While debugging and fixing stuff, I often find myself in the situation
> of adding more if/cond statements to a function and pushing the original
> body further in.  I think this usually leads to less clear code.

If this is only "while debugging and fixing stuff", I don't think it's
a serious enough problem to warrant such a change.  Note that my
preference to stick with the current situation in his respect is not
just out of inertia but also because I like a more functional style
of programming: usually/often you can find a formulation that's just as
elegant without the need for an early exit.

> This isn't the only use case, of course.  A lot of functions in Emacs go
> through pretty awkward contortions to end loops when certain conditions
> occur.

I tend to agree that early exit from loops would be sometimes welcome.
Currently, people either use catch/throw, or contortions, or just decide
not to exit early.  Also our while loops have no way to return a value,
so a `return' from a while loop can make the code *more* functional.
In functional programming language early exit constructs are rarely
needed because loops are written using recursion, so it's easy to exit
early: just don't recurse.  One constructs which would improve the
situation (without adding early exits) would be to add an `until': it's
just like `while' except that the condition is reversed *and* that the
non-nil final condition is returned as value of the `until' expression.
Very often (until (progn foo bar) baz) works well.  But I'd be OK with
adding a `return' from while loops: after all `while' loops are
naturally imperative, so such a `return' would not make things
less imperative.


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