Ocaml Pattern Matching

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OCaml pattern matching Tuples and lists CS235 Languages and Automata Department of Computer Science Wellesley College Lists in Java and OCaml Java OCaml empty() [] preprend(x, ys) x :: ys head(xs) List.hd(xs) tail(xs) List.tl(xs) isEmpty(xs) xs = [] *Note that [exp1; exp2; … ; expn] is an OCaml abbreviation for exp1 :: exp2 :: … :: expn :: []. Pattern matching 8-2 1 Summing an IntList in Java // Returns the integer sum of all element in ns public static int sumList (IntList ns) { if (IntList.isEmpty(ns) { return 0; } else { return IntList.head(ns) + sum(IntList.tail(ns));; } } s1 91 0 -22 Ø Pattern matching 8-3 Summing an integer list in OCaml # let rec sum ns = if ns = [] then 0 else List.hd(ns) + (sum (List.tl ns));; Pattern matching 8-4 2 Summing an integer list in OCaml # let rec sum ns = match ns with [] -> 0 | (n :: ns’) -> n + sum(ns’);; # sum [];; # sum [3];; # sum [3;2;7;5];; Pattern matching 8-5 range lo hi # range 3 7;; _: int list = [3;4;5;6;7] # range 5 5;; _: int list = [5] # range 6 5;; _: int list = [] *Returns a list of integers from lo up to hi, inclusive. The list is empty is lo > hi. Pattern matching 8-6 3 squares ns # squares [3;1;5;4;2];; _: int list = [9; 1; 25; 16; 4] # squares [5];; _: int list = [25] # squares [];; _: int list = [] # squares (range 3 6);; _: int list = [9; 16; 25; 36] Pattern matching 8-7 map f # let square x = x*x;; val square : int -> int = <fun> # square 3;; _: int = 9 # let rec map f = function [] -> [] | x :: xs -> f x :: map f xs;; val map : ('a -> 'b) -> 'a list -> 'b list = <fun> # map square (range 3 6);; - : int list = [9; 16; 25; 36] Pattern matching 8-8 4 isSorted xs # isSorted [];; _: bool = true # isSorted [3];; _: bool = true # isSorted [3;1;4;2];; _: bool = false # isSorted [1;2;3;4;5;6];; _: bool = true Pattern matching 8-9 Tuples # let t4 = (2 * 3, 4 < 5, "foo" ^ "bar", String.get "baz" 2);; # let w,x,y,z = t4;; # let first (x,_,_,_) = x;; # let last (_,_,_,z) = z;; Pattern matching 8-10 5 OCaml simplicity # let swap (a,b) = (b,a);; # swap (1+2,3=4);; # swap(swap(1+2,3=4));; Pattern matching 8-11 isMember (x,ys) # isMember(3, [5;2;3;1;4]);; _: bool = true # isMember(6, [5;2;3;1;4]);; _: bool = false # isMember(“be”, [“to”;”be”;”or”;”not”;”to”;”be”]);; _: bool = true # isMember((2,”too”),[(3,”three”);(1,”one”);(2,”two”)]);; _: bool = false Pattern matching 8-12 6.

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Pattern Matching Using Similarity Measures
Pattern matching using similarity measures Patroonvergelijking met behulp van gelijkenismaten (met een samenvatting in het Nederlands) PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van Rector Magnificus, Prof. Dr. H. O. Voorma, ingevolge het besluit van het College voor Promoties in het openbaar te verdedigen op maandag 18 september 2000 des morgens te 10:30 uur door Michiel Hagedoorn geboren op 13 juli 1972, te Renkum promotor: Prof. Dr. M. H. Overmars Faculteit Wiskunde & Informatica co-promotor: Dr. R. C. Veltkamp Faculteit Wiskunde & Informatica ISBN 90-393-2460-3 PHILIPS '$ The&&% research% described in this thesis has been made possible by financial support from Philips Research Laboratories. The work in this thesis has been carried out in the graduate school ASCI. Contents 1 Introduction 1 1.1Patternmatching.......................... 1 1.2Applications............................. 4 1.3Obtaininggeometricpatterns................... 7 1.4 Paradigms in geometric pattern matching . 8 1.5Similaritymeasurebasedpatternmatching........... 11 1.6Overviewofthisthesis....................... 16 2 A theory of similarity measures 21 2.1Pseudometricspaces........................ 22 2.2Pseudometricpatternspaces................... 30 2.3Embeddingpatternsinafunctionspace............. 40 2.4TheHausdorffmetric........................ 46 2.5Thevolumeofsymmetricdifference............... 54 2.6 Reflection visibility based distances . 60 2.7Summary.............................. 71 2.8Experimentalresults.......................
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CSCI 2041: Pattern Matching Basics
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Compiling Pattern Matching to Good Decision Trees
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Pattern Matching
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