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(define-library (csc loop)
(export loop return)
(import (scheme base))
(begin
(define-syntax initial-values
(syntax-rules (=
by
collect
do
for
from
in
into
then
to)
((initial-values loop-name (acc* ...) ((for _ in l temp-name) clause clause* ...) body)
(initial-values loop-name (acc* ... (temp-name l)) (clause clause* ...) body))
((initial-values loop-name (acc* ...) ((for x from start to _ by _) clause clause* ...) body)
(initial-values loop-name (acc* ... (x start)) (clause clause* ...) body))
((initial-values loop-name (acc* ...) ((for x = init then consequent) clause clause* ...) body)
(initial-values loop-name (acc* ... (x init)) (clause clause* ...) body))
((initial-values loop-name (acc* ...) ((collect _ into l last) clause clause* ...) body)
(initial-values loop-name (acc* ... (l '()) (last #f)) (clause clause* ...) body))
((initial-values loop-name (acc* ...) ((collect _ l last)) body)
(let loop-name (acc* ... (l '()) (last #f))
body))
((initial-values loop-name (acc* ...) ((do _)) body)
(let loop-name (acc* ...)
body))))
(define-syntax subsequent-values
(syntax-rules (=
by
collect
do
for
from
in
into
then
to)
((subsequent-values loop-name (acc* ...) (for _ in _ l) clause clause* ...)
(subsequent-values loop-name (acc* ... (cdr l)) clause clause* ...))
((subsequent-values loop-name (acc* ...) (for x from _ to _ by inc) clause clause* ...)
(subsequent-values loop-name (acc* ... (+ x inc)) clause clause* ...))
((subsequent-values loop-name (acc* ...) (for x = _ then consequent) clause clause* ...)
(subsequent-values loop-name (acc* ... consequent) clause clause* ...))
((subsequent-values loop-name (acc* ...) (collect expr into l last) clause clause* ...)
(if last
(begin
(set-cdr! last (list expr))
(subsequent-values loop-name (acc* ... l (cdr last)) clause clause* ...))
(begin
(set! l (list expr))
(subsequent-values loop-name (acc* ... l l) clause clause* ...))))
((subsequent-values loop-name (acc* ...) (collect expr l last))
(if last
(begin
(set-cdr! last (list expr))
(loop-name acc* ... l (cdr last)))
(begin
(set! l (list expr))
(loop-name acc* ... l l))))
((subsequent-values loop-name (acc* ...) (do expr))
(begin
expr
(loop-name acc* ...)))))
(define-syntax condition
(syntax-rules (=
by
collect
for
from
in
into
then
to)
((condition)
#t)
((condition (for _ in _ l) clause* ...)
(and (pair? l) (condition clause* ...)))
((condition (for x from _ to limit by _) clause* ...)
(and (<= x limit) (condition clause* ...)))
((condition (for _ = _ then _) clause* ...)
(condition clause* ...))
((condition (collect _ into _ _) clause* ...)
(condition clause* ...))))
(define-syntax result
(syntax-rules (collect)
((result (collect _ l _))
l)
((result (do _))
(if #f #f))))
(define-syntax bindings
(syntax-rules (=
by
collect
for
from
in
into
then
to)
((bindings () body)
body)
((bindings ((for x in _ l) clause* ...) body)
(let ((x (car l)))
(bindings (clause* ...)
body)))
((bindings ((for _ from _ to _ by _) clause* ...) body)
(bindings (clause* ...) body))
((bindings ((for _ = _ then _) clause* ...) body)
(bindings (clause* ...) body))
((bindings ((collect _ into _ _) clause* ...) body)
(bindings (clause* ...) body))))
(define (*current-loop-continuation* . args)
(error "Can't use return outside of a loop"))
(define-syntax loop-clauses
(syntax-rules ()
((loop-clauses (clause* ...) fin body)
(call/cc
(lambda (k)
(define prev-loop-continuation *current-loop-continuation*)
(dynamic-wind
(lambda ()
(set! *current-loop-continuation* k))
(lambda ()
(initial-values loop-name () (clause* ... body)
(if (condition clause* ...)
(bindings (clause* ...)
(subsequent-values loop-name () clause* ... body))
(begin
fin
(result body)))))
(lambda ()
(set! *current-loop-continuation* prev-loop-continuation))))))))
(define-syntax clause-collector
(syntax-rules (=
by
collect
do
finally
for
from
in
into
then
to)
((clause-collector (acc ...) fin for x in l clause clause* ...)
(clause-collector (acc ... (for x in l temp-name)) fin clause clause* ...))
((clause-collector (acc ...) fin for x from start to limit by step clause clause* ...)
(clause-collector (acc ... (for x from start to limit by step)) fin clause clause* ...))
((clause-collector (acc ...) fin for x from start to limit clause clause* ...)
(clause-collector (acc ... (for x from start to limit by 1)) fin clause clause* ...))
((clause-collector (acc ...) fin for x = init then subsequent clause clause* ...)
(clause-collector (acc ... (for x = init then subsequent)) fin clause clause* ...))
((clause-collector (acc ...) fin collect x into l clause clause* ...)
(clause-collector (acc ... (collect x into l temp-name)) fin clause clause* ...))
((clause-collector (acc ...) #f finally expr)
(loop-clauses (acc ...) expr (do (if #f #f))))
((clause-collector (acc ...) #f finally expr clause clause* ...)
(clause-collector (acc ...) expr clause clause* ...))
((clause-collector (acc ...) fin collect expr)
(loop-clauses (acc ...) fin (collect expr temp1 temp2)))
((clause-collector (acc ...) fin do body body* ...)
(loop-clauses (acc ...) fin (do (let () body body* ...))))))
; loop is a general purpose looping construct cribbed from CL.
(define-syntax loop
(syntax-rules ()
((loop clause clause* ...)
(clause-collector () #f clause clause* ...))))
(define-syntax return
(syntax-rules ()
((return expr)
(call-with-values (lambda () expr) *current-loop-continuation*))))))
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