Re: Guile: What's wrong with this?

[Ian Price]

Mark H Weaver <address@hidden> writes:

> As I understand it, in the Scheme standards (at least before R6RS's
> immutable pairs) the rationale behind marking literal constants as
> immutable is solely to avoid needlessly making copies of those literals,
> while flagging accidental attempts to modify them, since that is almost
> certainly a mistake.
Erm, if you don't count literals, which were already immutable, then
R6RS doesn't have immutable pairs. It does move the mutators to a
separate module, but that is a not really equivalent, because even if
you don't import (rnrs mutable-pairs), another module may mutate pairs
returned by your library. Ditto for strings,etc.

To quote section 5.10
"Literal constants, the strings returned by symbol->string, records with
no mutable fields, and other values explicitly designated as immutable
are immutable objects, while all objects created by the other procedures
listed in this report are mutable."

-- 
Ian Price

"Programming is like pinball. The reward for doing it well is
the opportunity to do it again" - from "The Wizardy Compiled"