Suggestion: nix VALUES in favor of DOT
Alpha Petrofsky 16 May 2005 22:01 UTC
The current draft of the srfi says:
let-values suffers from "parenthesis complexity"
The proposed syntax fixes the parenthesis complexity for fixed-arity
cases, but it clearly still suffers from parenthesis complexity in the
variable-arity case. As proof of this, I offer the fact that the
syntax's own designer screwed up the parentheses in two out of three
of the examples given for variable-arity clauses:
The syntactic keyword values allows receiving all values as in (let
((values . xs) (foo x)) body). It also allows receiving no values at
all as in (let ((values) (for-each foo list)) body).
Those should be (let (((values . xs) (foo x))) body) and (let
(((values) (for-each foo list))) body), according to the specification
given later in the srfi.
To avoid that mentally taxing triple-open-paren, you could use a
keyword named DOT rather than VALUES, with a syntax like so:
(let ((a b dot c (unlist '(1 2 3 4)))) c) => (3 4)
(let ((dot x (unlist '(1 2 3 4)))) x) => (1 2 3 4)
I don't think you need a special case for exactly zero values, because
that's a fixed-arity case. Why not allow this?:
(let ((<zero-valued-expression>)) <body>)
Here's some BNF:
<binding spec> --> (<variable>* <expression>)
<binding spec> --> (<variable>* dot <variable> <expression>)
Whether or not DOT would be the best choice of identifier for this, I
don't know. Here are the identifiers I considered:
dot
rest
&rest
&
rest=>
stick-the-rest-of-the-values-into-this-variable-to-my-right=>
=>
-al
