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Re: Prefix, not postfix
Date: Tue, 11 Apr 2006 18:22:37 -0400
From: Marc Feeley <email@example.com>
I'm not sure I understand your point. I'm advocating for a colon
suffix. SRFI 42 uses a colon prefix on identifiers (which by the way
is illegal in R5RS except for a lone colon). So keyword objects
using a colon suffix syntax do not hinder in any way SRFI 42 or any
R5RS compliant code, but a colon prefix syntax does.
My point is just that changing the meaning of a colon as either a
prefix or a suffix will break some existing R5RS-compliant code.
According to R5RS section 7.1.1, a trailing colon is most certainly
allowed in identifiers:
<identifier> ---> <initial> <subsequent>* | <peculiar identifier>
<initial> ---> <letter> | <special initial>
<special initial> ---> ... | `:' | ...
<subsequent> ---> <initial> | <digit> | <special subsequent>
Since `:' is a special initial, it is also an initial, and
transitively also a subsequent; it may therefore be used at the end of
an identifier, according to the rule for <identifier>.
I know that some code has used colon suffixes on identifiers (for
example the withdrawn iota: function in SRFI 1), but there are very
few uses of this and it is not portable anyway so I don't think this
argument has much weight.
Not portable? Only to Scheme systems that are already non-compliant.
Of the Schemes I use regularly, all allow colon suffixes in