ML for the Working Programmer

Transcription

1 ML for the Working Programmer 2nd edition Lawrence C. Paulson University of Cambridge CAMBRIDGE UNIVERSITY PRESS

2 CONTENTS Preface to the Second Edition Preface xiii xv 1 Standard ML 1 Functional Programming Expressions versus commands Expressions in procedural programming languages Storage management Elements of a functional language The efficiency of functional programming 9 Standard ML The evolution of Standard ML The ML tradition of theorem proving The new standard library ML and the working programmer 15 2 Names, Functions and Types 17 Chapter outline 18 Value declarations Naming constants Declaring functions Identifiers in Standard ML 21 Numbers, character strings and truth values Arithmetic Strings and characters Truth values and conditional expressions 26 Pairs, tuples and records Vectors: an example of pairing Functions with multiple arguments and results Records 32

3 vi Contents 2.10 Infix operators The evaluation of expressions 2.11 Evaluation in ML: call-by-value 2.12 Recursive functions under call-by-value 2.13 Call-by-need, or lazy evaluation Writing recursive functions Local Raising to an integer power Fibonacci numbers Integer square roots declarations Example: real square roots Hiding declarations using local Simultaneous declarations Introduction to modules The complex numbers Structures. Signatures Polymorphic type checking 2.23 Type inference 2.24 Polymorphic function declarations Summary of main points Lists Chapter outline Introduction to lists 3.1 Building a list 3.2 Operating on a list Some fundamental list functions 3.3 Testing lists and taking them apart 3.4 List processing by numbers 3.5 Append and reverse 3.6 Lists of lists, lists of pairs Applications of lists Making change Binary arithmetic Matrix transpose Matrix multiplication Gaussian elimination Writing a number as the sum of two squares "

4 Contents vn 3.13 The problem of the next permutation 95 The equality test in polymorphic functions Equality types Polymorphic set operations Association lists Graph algorithms 102 Sorting: A case study Random numbers Insertion sort Quicksort Merge sort 111 Polynomial arithmetic Representing abstract data Representing polynomials Polynomial addition and multiplication The greatest common divisor 119 Summary of main points Trees and Concrete Data 123 Chapter outline 123 The datatype declaration The King and his subjects ; J Enumeration types Polymorphic datatypes Pattern-matching with val, as, case 130 Exceptions..: Introduction to exceptions Declaring exceptions - s Raising exceptions Handling exceptions Objections to exceptions 140 Trees : A type for binary trees Enumerating the contents of a tree ;, Building a tree from a list A structure for binary trees 148 Tree-based data structures Dictionaries '' ' Functional and flexible arrays 154

5 viii Contents 4.16 Priority queues, 159 A tautology checker Propositional Logic Negation normal form Conjunctive normal form 167 Summary of main points 170 Functions and Infinite Data 171 Chapter outline, 171 Functions as values Anonymous functions with fn notation ^ Curried functions, Functions in data structures Functions as arguments and results 177 General-purpose functionals Sections Combinators The list functionals map and filter The list functionals takewhile and dropwhile The list functionals exists and all The list functionals/<?w/ andfoldr More examples of recursive functionals 188 Sequences, or infinite lists A type of sequences Elementary sequence processing Elementary applications of sequences Numerical computing Interleaving and sequences of sequences 201 Search strategies and infinite lists Search strategies in ML Generating palindromes The Eight Queens problem Iterative deepening 210 Summary of main points 211 Reasoning About Functional Programs 213 Chapter outline 213 Some principles of mathematical proof T ML programs and mathematics 214

6 Contents 1X 6.2 Mathematical induction and complete induction Simple examples of program verification 220 Structural induction Structural induction on lists Structural induction on trees Function values and functionals 233 A general induction principle Computing normal forms Well-founded induction and recursion Recursive program schemes 246 Specification and verification An ordering predicate Expressing rearrangement through multisets The significance of verification 254 Summary of main points 256 Abstract Types and Functors 257 Chapter outline 258 Three representations of queues Representing queues as lists Representing queues as a new datatype Representing queues as pairs of lists 261 Signatures and abstraction The intended signature for queues Signature constraints The abstype declaration Inferred signatures for structures 269 Functors Testing the queue structures Generic matrix arithmetic Generic dictionaries and priority queues 280 Building large systems using modules Functors with multiple arguments Sharing constraints Fully-functorial programming The open declaration Signatures and substructures 305 Reference guide to modules The syntax of signatures and structures 309

7 Contents 7.17 The syntax of module declarations. 311 Summary of main points Imperative Programming in ML 313 Chapter outline 313 Reference types References and their operations Control structures Polymorphic references 321 References in data structures, Sequences, or lazy lists , Ring buffers Mutable and functional arrays 335 Input and output String processing ',, Text input/output Text processing examples A pretty printer 351 Summary of main points Writing Interpreters for the A-Calculus 357 Chapter outline 357 A functional parser Scanning, or lexical analysis A toolkit for top-down parsing The ML code of the parser Example: parsing and displaying types 367 Introducing the A,-calculus A,-terms and ^.-reductions Preventing variable capture in substitution 375 Representing X-terms in ML The fundamental operations Parsing X-terms Displaying A-terms 382 The ^.-calculus as a programming language Data structures in the A.-calculus Recursive definitions in the X-calculus The evaluation of X-terms Demonstrating the evaluators 393

8 Contents xi Summary of main points A Tactical Theorem Prover 397 Chapter outline 397 A sequent calculus for first-order logic The sequent calculus for propositional logic Proving theorems in the sequent calculus Sequent rules for the quantifiers Theorem proving with quantifiers 404 Processing terms and formulae in ML Representing terms and formulae Parsing and displaying formulae Unification 416 Tactics and the proof state The proof state The ML signature Tactics for basic sequents The propositional tactics The quantifier tactics 428 Searching for proofs Commands for transforming proof states Two sample proofs using tactics Tacticals Automatic tactics for first-order logic 440 Summary of main points 444 Project Suggestions 445 Bibliography 449 Syntax Charts 457 Index 469