[Chicken-users] Binding identifiers with set!

[Category 5]

In <address@hidden> on
comp.lang.scheme, Anton van Straaten pointed out that set! can be used
to introduce new bindings in Chicken:

% csi
; This is the CHICKEN interpreter.
; Version 1, Build 17 - netbsd-gnu-ultrasparc
; (c)2000-2003 Felix L. Winkelmann
>>> foo
Error: unbound variable: foo
>>> (set! foo 1)
>>> foo
1
>>>

This clearly doesn't jive with R5RS (5.2.1):

    At the top level of a program, a definition

    (define <variable> <expression>)

    has essentially the same effect as the assignment expression

    (set! <variable> <expression>)

    if <variable> is bound. If <variable> is not bound, however, then
    the definition will bind <variable> to a new location before
    performing the assignment, whereas it would be an error to perform a
    set! on an unbound variable.

How do people feel about this?  I find the behaviour a bit worrying, as
it amounts to the omission of a basic form of error checking supported
by R5RS as well as every other implementation I'm aware of.  I can
imagine situations where this would bite.

My first choice would be to see set! changed to support the more
restrictive semantics, but failing that, I think the current behaviour
should be explicitly documented in the "Deviations from the standard"
section of the manual.

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