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This module is inspired by
Roshan James' "call/cc based implementation of Yield the Magnificent for Scheme".
Iterators are implemented with the macro lambda-yield and accessed with the macro iterate. Both are unhygienic by design.
They are then packaged into a coroutine record.
- iterators #!optional symprocedure
documentation-procedure; returns the list of exported symbols if called with no symbol, otherwise the signature of that exported symbol sym.
- (lambda-yield args xpr . xprs)syntax
A curried lambda, which can yield a value in its body. Not hygienic because of yield.
- (define-iterator (name . args) xpr . xprs)syntax
Defines a procedure, name, with lambda-yield instead of lambda. Not hygienic because of yield.
- (iterate iterator xpr . xprs)syntax
invokes xpr . xprs whenever the iterator yields. Not hygienic, exports 'break' and 'it'; 'it' is the result of a yield and 'break' an escape-procedure.
- (yield-all iterator)syntax
yield all values of an interator, equivalent to (iterate iterator (yield it)), not hygienic because of yield.
A coroutine wraps an iterator into a coroutine object.
- coroutine iteratorprocedure
packages the iterator, i.e. a unary procedure of the yield argument, into a coroutine and does a first move, so that the coroutine object contains an escape-procedure
- coroutine? xprprocedure
- co-move coprocedure
iterates internal iterator till it yields or till it returns; returns new coroutine
- co-value coprocedure
returns the value of a coroutine.
- co-finished? coprocedure
has coroutine finished execution?
- co-not-finished? coprocedure
is coroutine's iterator still running?
- co-return val coprocedure
sets a return value into the coroutine and returns the new coroutine. This return value can be yielded by the internal iterator
- coroutines #!rest itersprocedure
equivalent to (map coroutine iters), hence returns many coroutines.
- co-all-finished? cosprocedure
did all internal iterators finish?
- co-any-finished? cosprocedure
did some internal iterator finish?
- co-none-finished? cosprocedure
are all internal iterators still running?
- co-values cosprocedure
equivalent to (map co-value cos).
- co-move-all cosprocedure
equivalent to (map co-move cos).
- co-return-all ret cosprocedure
equivalent to (map (lambda (co) (co-return ret co)) cos).
(import iterators) (define-iterator (evens) (let loop ((i 0)) (loop (+ (yield i) 2)))) (iterate (evens) (print "it = " it) (if (>= it 20) (break #f) it)) ;;; tree-walking (define-iterator (walk-tree tree) (cond ((pair? tree) (yield-all (walk-tree (car tree))) (yield-all (walk-tree (cdr tree)))) ((null? tree) '()) (else (yield tree)))) (iterate (walk-tree '(1 2 3 (5 6 7) (4 5) 8)) (print "value " it))) (define (same-fringe? t1 t2) (let loop ((c1 (coroutine (walk-tree t1))) (c2 (coroutine (walk-tree t2)))) ;(print "XXX " (co-value c1) " " (co-value c2)) (if (and (co-finished? c1) (co-finished? c2)) #t (if (or (co-finished? c1) (co-finished? c2)) #f (if (eq? (co-value c1) (co-value c2)) (loop (co-move c1) (co-move c2)) #f))))) (define (Same-fringe? t1 t2) (let loop ((cs (coroutines (walk-tree t1) (walk-tree t2)))) ;(print "YYY " (co-values cs)) (cond ((co-all-finished? cs) #t) ((co-any-finished? cs) #f) ((eq? (co-value (car cs)) (co-value (cadr cs))) (loop (co-move-all cs))) (else #f)))) (define-iterator (ping) (let loop () (yield 'ping) (loop))) (define-iterator (pong) (let loop () (yield 'pong) (loop))) (define (ping-pong n) (let loop ((k 0) (ci (coroutine (ping))) (co (coroutine (pong)))) (cond ((= k n) (print 'Finish)) ((< k n) (print (co-value ci) " " (co-value co)) (loop (+ k 1) (co-move ci) (co-move co)))))) (ping-pong 20)
Oct 11, 2019
Copyright (c) 2019, Juergen Lorenz All rights reserved.
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- initial version