> define-syntax list-of
> syntax-rules (is in)
> ; base case
> \
> . list-of x
> . \ list x
> ; handle (var in x) clause
> \
> . list-of x
> . var in expr
> . clauses \ ...
> . \ concatenate
> . . map
> . . lambda (var)
> . . list-of x
> . . clauses \ ...
> . . expr
> ; handle (var is x) clause
> \
> . list-of x
> . var is expr
> . clauses \ ...
> . \ let ((var expr))
> . . list-of x
> . . clauses \ ...
> ; handle (pred? x) clause
> \
> . list-of x
> . pred?(args ...)
> . clauses \ ...
> . \ if pred?(args ...)
> . . list-of x
> . . clauses \ ...
> . . '()
As a first experiment, let's see if I can easily recreate what this
translates to:
(define-syntax list-of
(syntax-rules (is in)
((list-of x)
(list x))
((list-of x (var in expr) clauses ...)
(concatenate (map (lambda (var) (list-of x clauses ...))
expr)))
((list-of x (var is expr) clauses ...)
(let ((var expr))
(list-of x clauses ...)))
((list-of x (pred? args ...) (clauses ...))
(if (pred? args ...)
(list-of x (clauses ...))
'()))))
Observations:
a) If this is right, why do we need the period-backslash construct, say in
the base case? Wouldn't just indentation (two periods) suffice?
b) Should we really have to insert a backslash in empty lines? Wart just
applies the enter-enter rule at the repl, not in batch mode. Did y'all
consider that?
c) Are the periods for indentation optional? It's confusing/distracting to
mix spaces with periods in the same code.
d) I notice that avoiding parens is *much* more compact. It lets me see the
global structure at a glance. Let me see if I can reconstruct that property
by bringing back some parens:
define-syntax list-of
syntax-rules (is in)
\ list-of x
list x
\ list-of x (var in expr) clauses ...
concatenate
map (lambda (var) (list-of x clauses ...))
expr
\ list-of x (var is expr) clauses ...
let ((var expr))
list-of x clauses ...
\ list-of x pred?(args ...) (clauses ...)
if pred?(args ...)
list-of x (clauses ...)
'()
Ok, I see why you need GROUP support :) It's because common lisp and scheme
use more parens than arc. I also found myself missing arc's syntax for
compose, so that I could say:
concatenate:map (lambda (var) (list-of x clauses ...))
expr
Is this translation correct? I'm not sure which proposal this maps to. Is
it subsumed by one of the suggestions?
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