======assoc.scm====== <code shell>#!/usr/bin/env racket #lang racket/base</code> viz [[racket>assoc]] assoc ((k1 . v1) (k2 . v2) ...) operace: (cons-assoc key val assoc) nastav nebo pridej [[PAPR1:L6#Asociativni_pole|assoc pole]] (assoc-key assoc key) hledej; racket: (assoc key alist) (assoc-del assoc key) zrus klic v rnrs je alist jako ((k v) (k v) ...) racket: (assoc key alist) -> (key ...) ;equal? racket: (assv key alist) -> (key ...) ;eqv? racket: (assq key alist) -> (key ...) ;eq? (exists pred list) (forall pred list) <code scheme> '(exists pomoci akumulace, foldl:) (define (exists p l) (foldl (lambda (e t) (if t ;uz nasli, vracej porad #t t (p e))) #f l)) (exists (lambda (x) (= x 1)) '(1 2 3)) (exists even? '(1 2 3)) (exists even? '(1 5 3)) </code> pomoci iterace lze jen and a or, viz [[PAPR1:L9]] <code scheme> '(exists pomoci iterace:) (define (exists-iter p l) (cond ((null? l) #f) ;prazdny seznam, nebo jsme na konci ((p (car l)) #t);nasli (else (exists-iter p (cdr l))))) (exists-iter (lambda (x) (= x 1)) '(1 2 3)) (exists-iter even? '(1 2 3)) (exists-iter even? '(1 5 3)) </code> pouzit exists str159, existuje? premapovat, jinak pridat (define (cons-assoc key val assoc) assoc) ;todo pomoci fold, iterace? sel by exist-iter inline jako letrec? NOTE: Lekce 6 jeste nezná akumulace, fold <code scheme> (define (cons-assoc key val assoc) (if (exists (lambda (x) (equal? key (car x))) assoc) ;existuje, najdeme a pre-map-ujeme (map (lambda (x) (if (equal? key (car x)) (cons key val) x)) assoc) ;nenasli, novy par (cons (cons key val) assoc))) (define al (cons-assoc 'a 1 '())) (cons-assoc 'a 2 al) (cons-assoc 'b 3 al);porad dva prvky!!! nemuze modifikovat al!!! (cons-assoc 'c 4 al);takze nabalovat se to muze rekurzi, fold-rem apod! (cons-assoc 'c 4 al) (cons-assoc 'd 5 '((d . 5))) </code> (collate: '(1 1 2 2 3 3 3) => ((1 . 1) (2 . 2) (3 . 3)) <code scheme> (define (collate l) ;vlastne upravene cons-assoc, reseni na urovni lekce 6 (foldl (lambda (e t) (if (exists (lambda (x) (equal? e (car x))) t) ;existuje, najdeme a inkrementujeme (map (lambda (x) (if (equal? e (car x)) (cons e (+ 1 (cdr x)));inkrementujeme x)) t) ;nenasli, novy par (cons (cons e 1) t))) '();term/kontext bude alist l)) (collate '(1 2 2 3 3 3)) ;=>((1 . 1) (2 . 2) (3 . 3)) (exit) </code> (sort lst less-than? [ #:key extract-key #:cache-keys? cache-keys?]) → list? lst : list? less-than? : (any/c any/c . -> . any/c) extract-key : (any/c . -> . any/c) = (lambda (x) x) cache-keys? : boolean? = #f <code scheme> (sort '(1 2 4 3) <) (sort '(1 2 4 3) >) (sort '((b . 2) (a . 1) (c . 3)) (lambda (x y) (< (cdr x) (cdr y)))) </code> prida nebo aktualizuje key val <code scheme> (define (cons-assoc-iter key val assoc) (if (null? assoc) (list (cons key val)) (foldl ;'rychlejsi' nez foldr, ale dela reverse! (lambda (e t) (if (equal? key (car e)) (cons (cons key val) t) ;#vymenime (cons-assoc-iter key val (cons e t))));#kopirujeme a hledame dal '() assoc))) '(cons-assoc-iter k v al) (cons-assoc-iter 1 1 '()) (cons-assoc-iter 1 2 '((1 . 1))) (cons-assoc-iter 2 2 '((1 . 1))) ; vim: syntax=racket </code>