On 08/16/2015 07:56 AM, John Cowan wrote:
> What do you think about using `!` instead of `set!` and `$` instead of
> `ref`?  They are very short, preserve the !-convention, fit in nicely
> with Gauche's `~`, and aren't much used in existing Schemes.  I ran them
> through my 47 Schemes, and found only these:
>
> Schemik excludes `$` from symbols, but doesn't seem to use it otherwise.
>
> Llava uses `!` as a synonym for `not`.
>
> Elk binds `!` to the value of the last expression evaluated at the REPL.
>
> Inlab has a procedure `!` which invokes an editor on the last expression
> typed at the REPL and evaluates it.
>
> Owl Lisp uses `!` for the factorial function.

Kawa uses '!' as (roughly) a synonym for define.  A separate operator
is needed to avoid ambiguity with the function-defining variants of define.
Also, 'let'/'let*'/''letrec' and 'define' are too verbose.

(! PATTERN VALUE)
Evaluate VALUE and bind against the PATTERN.  Most commonly PATTERN is
a simple identifier (in which case it's like a 'define'), but it can
include a type specifier or be a complex pattern.
'|' also implies the bound names are constant (non-assignable)
and local by default.  (I.e. a file-level name is not exported.)
'!' also disallows overriding definitions, to catch common errors,
though this feature may need some tweaking.

There is also:
(? PATTERN VALUE)
Can only be used in a conditional context (like an /if' or an 'and').
If the VALUE matches against the PATTERN then the bindings are available
if the 'then' clause of the 'if' (or in the case of an 'and', the
following sub-expressions), and the boolean value is true.

These extensions are relatively new: While the basic syntax was in the 2.0
release, it wasn't really documented, awaiting the more general pattern
framework, currently in the "invoke" Subversion branch.
--
	--Per Bothner
xxxxxx@bothner.com   http://per.bothner.com/