Programming Languages Thunks, Laziness, Streams, Memoization
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CSCI 2041: Lazy Evaluation
CSCI 2041: Lazy Evaluation Chris Kauffman Last Updated: Wed Dec 5 12:32:32 CST 2018 1 Logistics Reading Lab13: Lazy/Streams I Module Lazy on lazy Covers basics of delayed evaluation computation I Module Stream on streams A5: Calculon Lambdas/Closures I Arithmetic language Briefly discuss these as they interpreter pertain Calculon I 2X credit for assignment I 5 Required Problems 100pts Goals I 5 Option Problems 50pts I Eager Evaluation I Milestone due Wed 12/5 I Lazy Evaluation I Final submit Tue 12/11 I Streams 2 Evaluation Strategies Eager Evaluation Lazy Evaluation I Most languages employ I An alternative is lazy eager evaluation evaluation I Execute instructions as I Execute instructions only as control reaches associated expression results are needed code (call by need) I Corresponds closely to I Higher-level idea with actual machine execution advantages and disadvantages I In pure computations, evaluation strategy doesn’t matter: will produce the same results I With side-effects, when code is run matter, particular for I/O which may see different printing orders 3 Exercise: Side-Effects and Evaluation Strategy Most common place to see differences between Eager/Lazy eval is when functions are called I Eager eval: eval argument expressions, call functions with results I Lazy eval: call function with un-evaluated expressions, eval as results are needed Consider the following expression let print_it expr = printf "Printing it\n"; printf "%d\n" expr; ;; print_it (begin printf "Evaluating\n"; 5; end);; Predict results and output for both Eager and Lazy Eval strategies 4 Answers: Side-Effects and Evaluation Strategy let print_it expr = printf "Printing it\n"; printf "%d\n" expr; ;; print_it (begin printf "Evaluating\n"; 5; end);; Evaluation > ocamlc eager_v_lazy.ml > ./a.out Eager Eval # ocaml’s default Evaluating Printing it 5 Lazy Eval Printing it Evaluating 5 5 OCaml and explicit lazy Computations I OCaml’s default model is eager evaluation BUT. -
Introduction to Programming in Lisp
Introduction to Programming in Lisp Supplementary handout for 4th Year AI lectures · D W Murray · Hilary 1991 1 Background There are two widely used languages for AI, viz. Lisp and Prolog. The latter is the language for Logic Programming, but much of the remainder of the work is programmed in Lisp. Lisp is the general language for AI because it allows us to manipulate symbols and ideas in a commonsense manner. Lisp is an acronym for List Processing, a reference to the basic syntax of the language and aim of the language. The earliest list processing language was in fact IPL developed in the mid 1950’s by Simon, Newell and Shaw. Lisp itself was conceived by John McCarthy and students in the late 1950’s for use in the newly-named field of artificial intelligence. It caught on quickly in MIT’s AI Project, was implemented on the IBM 704 and by 1962 to spread through other AI groups. AI is still the largest application area for the language, but the removal of many of the flaws of early versions of the language have resulted in its gaining somewhat wider acceptance. One snag with Lisp is that although it started out as a very pure language based on mathematic logic, practical pressures mean that it has grown. There were many dialects which threaten the unity of the language, but recently there was a concerted effort to develop a more standard Lisp, viz. Common Lisp. Other Lisps you may hear of are FranzLisp, MacLisp, InterLisp, Cambridge Lisp, Le Lisp, ... Some good things about Lisp are: • Lisp is an early example of an interpreted language (though it can be compiled). -
PUB DAM Oct 67 CONTRACT N00014-83-6-0148; N00014-83-K-0655 NOTE 63P
DOCUMENT RESUME ED 290 438 IR 012 986 AUTHOR Cunningham, Robert E.; And Others TITLE Chips: A Tool for Developing Software Interfaces Interactively. INSTITUTION Pittsburgh Univ., Pa. Learning Research and Development Center. SPANS AGENCY Office of Naval Research, Arlington, Va. REPORT NO TR-LEP-4 PUB DAM Oct 67 CONTRACT N00014-83-6-0148; N00014-83-K-0655 NOTE 63p. PUB TYPE Reports - Research/Technical (143) EDRS PRICE MF01/PC03 Plus Postage. DESCRIPTORS *Computer Graphics; *Man Machine Systems; Menu Driven Software; Programing; *Programing Languages IDENTIF7ERS Direct Manipulation Interface' Interface Design Theory; *Learning Research and Development Center; LISP Programing Language; Object Oriented Programing ABSTRACT This report provides a detailed description of Chips, an interactive tool for developing software employing graphical/computer interfaces on Xerox Lisp machines. It is noted that Chips, which is implemented as a collection of customizable classes, provides the programmer with a rich graphical interface for the creation of rich graphical interfaces, and the end-user with classes for modeling the graphical relationships of objects on the screen and maintaining constraints between them. This description of the system is divided into five main sections: () the introduction, which provides background material and a general description of the system; (2) a brief overview of the report; (3) detailed explanations of the major features of Chips;(4) an in-depth discussion of the interactive aspects of the Chips development environment; and (5) an example session using Chips to develop and modify a small portion of an interface. Appended materials include descriptions of four programming techniques that have been sound useful in the development of Chips; descriptions of several systems developed at the Learning Research and Development Centel tsing Chips; and a glossary of key terms used in the report. -
Allegro CL User Guide
Allegro CL User Guide Volume 1 (of 2) version 4.3 March, 1996 Copyright and other notices: This is revision 6 of this manual. This manual has Franz Inc. document number D-U-00-000-01-60320-1-6. Copyright 1985-1996 by Franz Inc. All rights reserved. No part of this pub- lication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means electronic, mechanical, by photocopying or recording, or otherwise, without the prior and explicit written permission of Franz incorpo- rated. Restricted rights legend: Use, duplication, and disclosure by the United States Government are subject to Restricted Rights for Commercial Software devel- oped at private expense as specified in DOD FAR 52.227-7013 (c) (1) (ii). Allegro CL and Allegro Composer are registered trademarks of Franz Inc. Allegro Common Windows, Allegro Presto, Allegro Runtime, and Allegro Matrix are trademarks of Franz inc. Unix is a trademark of AT&T. The Allegro CL software as provided may contain material copyright Xerox Corp. and the Open Systems Foundation. All such material is used and distrib- uted with permission. Other, uncopyrighted material originally developed at MIT and at CMU is also included. Appendix B is a reproduction of chapters 5 and 6 of The Art of the Metaobject Protocol by G. Kiczales, J. des Rivieres, and D. Bobrow. All this material is used with permission and we thank the authors and their publishers for letting us reproduce their material. Contents Volume 1 Preface 1 Introduction 1.1 The language 1-1 1.2 History 1-1 1.3 Format -
Open WATCOM Programmer's Guide
this document downloaded from... Use of this document the wings of subject to the terms and conditions as flight in an age stated on the website. of adventure for more downloads visit our other sites Positive Infinity and vulcanhammer.net chet-aero.com Watcom FORTRAN 77 Programmer's Guide Version 1.8 Notice of Copyright Copyright 2002-2008 the Open Watcom Contributors. Portions Copyright 1984-2002 Sybase, Inc. and its subsidiaries. All rights reserved. Any part of this publication may be reproduced, transmitted, or translated in any form or by any means, electronic, mechanical, manual, optical, or otherwise, without the prior written permission of anyone. For more information please visit http://www.openwatcom.org/ Portions of this manual are reprinted with permission from Tenberry Software, Inc. ii Preface The Watcom FORTRAN 77 Programmer's Guide includes the following major components: · DOS Programming Guide · The DOS/4GW DOS Extender · Windows 3.x Programming Guide · Windows NT Programming Guide · OS/2 Programming Guide · Novell NLM Programming Guide · Mixed Language Programming · Common Problems Acknowledgements This book was produced with the Watcom GML electronic publishing system, a software tool developed by WATCOM. In this system, writers use an ASCII text editor to create source files containing text annotated with tags. These tags label the structural elements of the document, such as chapters, sections, paragraphs, and lists. The Watcom GML software, which runs on a variety of operating systems, interprets the tags to format the text into a form such as you see here. Writers can produce output for a variety of printers, including laser printers, using separately specified layout directives for such things as font selection, column width and height, number of columns, etc. -
COMPILING FUNCTIONAL PROGRAMMING CONSTRUCTS to a LOGIC ENGINE by Harvey Abramson and Peter Ludemann Technical Report 86-24 November 1986
COMPILING FUNCTIONAL PROGRAMMING CONSTRUCTS TO A LOGIC ENGINE by Harvey Abramson and Peter Ludemann Technical Report 86-24 November 1986 Compiling Functional Programming Constructs to a Logic Engine Harvey Abramson t and Peter Ltidemann:I: Department of Computer Science University of British Columbia Vancouver, B.C., Canada V6T 1W5 Copyright © 1986 Abstract In this paper we consider how various constructs used in functional programming can be efficiently translated to code for a Prolog engine (designed by Ltidemann) similar in spirit but not identical to the Warren machine. It turns out that this Prolog engine which contains a delay mechanism designed to permit co routining and sound implementation of negation is sufficient to handle all common functional programming constructs; indeed, such a machine has about the same efficiency as a machine designed specifically for a functional programming language. This machine has been fully implemented. t Present address: Department of Computer Science, Bristol University, Bristol, England . f Present address: IBM Canada Ltd., 1 Park Centre, 895 Don Mills Road, North York, Ontario, Canada M3C 1W3 The proposals for combining the two paradigms Compiling Functional Programming have been roughly classified in [BoGi86] as being Constructs to a Logic Engine either functional plus logic or logic plus functional. Harvey Abramson t and Peter Ltidemanni In the former approach, invertibility, nondeterminism Department of Computer Science and unification are added to some higher order functional language; in the latter approach, first-order University of British Columbia functions are added to a first-order logic with an Vancouver, B.C., Canada V6T lWS equality theory. We do not take any position as to Copyright© 1986 which approach is best, but since a logic machine already deals with unification, nondeterminism and invertibility, we have taken, from an implementation Abstract viewpoint, the logic plus functional approach. -
Parameter Passing, Generics, Exceptions
Lecture 9: Parameter Passing, Generics and Polymorphism, Exceptions COMP 524 Programming Language Concepts Stephen Olivier February 12, 2008 Based on notes by A. Block, N. Fisher, F. Hernandez-Campos, and D. Stotts The University of North Carolina at Chapel Hill Parameter Passing •Pass-by-value: Input parameter •Pass-by-result: Output parameter •Pass-by-value-result: Input/output parameter •Pass-by-reference: Input/output parameter, no copy •Pass-by-name: Effectively textual substitution The University of North Carolina at Chapel Hill 2 Pass-by-value int m=8, i=5; foo(m); print m; # print 8 proc foo(int b){ b = b+5; } The University of North Carolina at Chapel Hill 3 Pass-by-reference int m=8; foo(m); print m; # print 13 proc foo(int b){ b = b+5; } The University of North Carolina at Chapel Hill 4 Pass-by-value-result int m=8; foo(m); print m; # print 13 proc foo(int b){ b = b+5; } The University of North Carolina at Chapel Hill 5 Pass-by-name •Arguments passed by name are re-evaluated in the caller’s referencing environment every time they are used. •They are implemented using a hidden-subroutine, known as a thunk. •This is a costly parameter passing mechanism. •Think of it as an in-line substitution (subroutine code put in-line at point of call, with parameters substituted). •Or, actual parameters substituted textually in the subroutine body for the formulas. The University of North Carolina at Chapel Hill 6 Pass-by-name array A[1..100] of int; array A[1..100] of int; int i=5; int i=5; foo(A[i], i); foo(A[i]); print A[i]; #print A[6]=7 -
S Allegro Common Lisp Foreign Function Interface
Please do not remove this page Extensions to the Franz, Inc.'s Allegro Common Lisp foreign function interface Keane, John https://scholarship.libraries.rutgers.edu/discovery/delivery/01RUT_INST:ResearchRepository/12643408560004646?l#13643533500004646 Keane, J. (1996). Extensions to the Franz, Inc.’s Allegro Common Lisp foreign function interface. Rutgers University. https://doi.org/10.7282/t3-pqns-7h57 This work is protected by copyright. You are free to use this resource, with proper attribution, for research and educational purposes. Other uses, such as reproduction or publication, may require the permission of the copyright holder. Downloaded On 2021/09/29 22:58:32 -0400 Extensions to the Franz Incs Allegro Common Lisp Foreign Function Interface John Keane Department of Computer Science Rutgers University New Brunswick NJ keanecsrutgersedu January Abstract As provided by Franz Inc the foreign function interface of Allegro Com mon Lisp has a number of limitations This pap er describ es extensions to the interface that facilitate the inclusion of C and Fortran co de into Common Lisp systems In particular these extensions make it easy to utilize libraries of numerical subroutines such as those from Numerical Recip es in C from within ACL including those routines that take functions as arguments A mechanism for creating Lisplike dynamic runtime closures for C routines is also describ ed Acknowledgments The research presented in this do cument is supp orted in part by NASA grants NCC and NAG This research is also part of the Rutgers based -
Control Flow
Control Flow COMS W4115 Prof. Stephen A. Edwards Spring 2002 Columbia University Department of Computer Science Control Flow “Time is Nature’s way of preventing everything from happening at once.” Scott identifies seven manifestations of this: 1. Sequencing foo(); bar(); 2. Selection if (a) foo(); 3. Iteration while (i<10) foo(i); 4. Procedures foo(10,20); 5. Recursion foo(int i) { foo(i-1); } 6. Concurrency foo() jj bar() 7. Nondeterminism do a -> foo(); [] b -> bar(); Ordering Within Expressions What code does a compiler generate for a = b + c + d; Most likely something like tmp = b + c; a = tmp + d; (Assumes left-to-right evaluation of expressions.) Order of Evaluation Why would you care? Expression evaluation can have side-effects. Floating-point numbers don’t behave like numbers. Side-effects int x = 0; int foo() { x += 5; return x; } int a = foo() + x + foo(); What’s the final value of a? Side-effects int x = 0; int foo() { x += 5; return x; } int a = foo() + x + foo(); GCC sets a=25. Sun’s C compiler gave a=20. C says expression evaluation order is implementation-dependent. Side-effects Java prescribes left-to-right evaluation. class Foo { static int x; static int foo() { x += 5; return x; } public static void main(String args[]) { int a = foo() + x + foo(); System.out.println(a); } } Always prints 20. Number Behavior Basic number axioms: a + x = a if and only if x = 0 Additive identity (a + b) + c = a + (b + c) Associative a(b + c) = ab + ac Distributive Misbehaving Floating-Point Numbers 1e20 + 1e-20 = 1e20 1e-20 1e20 (1 + 9e-7) + 9e-7 6= 1 + (9e-7 + 9e-7) 9e-7 1, so it is discarded, however, 1.8e-6 is large enough 1:00001(1:000001 − 1) 6= 1:00001 · 1:000001 − 1:00001 · 1 1:00001 · 1:000001 = 1:00001100001 requires too much intermediate precision. -
210 CHAPTER 7. NAMES and BINDING Chapter 8
210 CHAPTER 7. NAMES AND BINDING Chapter 8 Expressions and Evaluation Overview This chapter introduces the concept of the programming environment and the role of expressions in a program. Programs are executed in an environment which is provided by the operating system or the translator. An editor, linker, file system, and compiler form the environment in which the programmer can enter and run programs. Interac- tive language systems, such as APL, FORTH, Prolog, and Smalltalk among others, are embedded in subsystems which replace the operating system in forming the program- development environment. The top-level control structure for these subsystems is the Read-Evaluate-Write cycle. The order of computation within a program is controlled in one of three basic ways: nesting, sequencing, or signaling other processes through the shared environment or streams which are managed by the operating system. Within a program, an expression is a nest of function calls or operators that returns a value. Binary operators written between their arguments are used in infix syntax. Unary and binary operators written before a single argument or a pair of arguments are used in prefix syntax. In postfix syntax, operators (unary or binary) follow their arguments. Parse trees can be developed from expressions that include infix, prefix and postfix operators. Rules for precedence, associativity, and parenthesization determine which operands belong to which operators. The rules that define order of evaluation for elements of a function call are as follows: • Inside-out: Evaluate every argument before beginning to evaluate the function. 211 212 CHAPTER 8. EXPRESSIONS AND EVALUATION • Outside-in: Start evaluating the function body. -
Exam 1 Review: Solutions Capture the Dragons
CSCI 1101B: Introduction to Computer Science Instructor: Prof. Harmon Exam 1 Review: Solutions Capture the Dragons Boolean Expressions 1. Of the following, which are Boolean expressions? (a)2+3 Not Boolean (b)2>3 Boolean (c) num >= 2 Boolean (d) num1 = num2 Not Boolean 2. If x = 3, and x <= y evaluates to True, what values can y have? y >= 3 3. Simplify each of the following expressions: (a) my_num or True Depends on what the value of my_num is. See rules as in #5. (b) False and "Mary" or True True (c) False and ("Mary" or True) False 4. Is x =< y the same as x <= y? No. Python only recognizes the latter. The former is invalid syntax. 5. If x = 1 and y = 2, explain the following results: (a) >>> x and y # = 2 (b) >>> x or y # = 1 Python uses lazy evaluation. • The expression x and y first evaluates x. If x is equivalent to False (or empty/zero), its value is returned. Otherwise, y is evaluated and the resulting value is returned. • The expression x or y first evaluates x. If x is equivalent to True (or non-empty/nonzero), its value is returned. Otherwise, y is evaluated and the resulting value is returned. 1 CSCI 1101B: Introduction to Computer Science Exam 1 Review: Solutions Conditionals 1. What is indentation, and how is it related to the concept of a code block? Indentation is the placement of text (to the left or right). Python uses indenta- tion to associate code into groups, or blocks. 2. What is the difference between a chained conditional and a nested conditional? Chained => if, elif, else Nested => conditionals exist (are "nested") inside each other 3. -
A Quick Introduction to Common Lisp
CSC 244/444 Notes last updated Feb 3, 2020 A Quick Introduction to Common Lisp Lisp is a functional language well-suited to sym- bolic AI, based on the λ-calculus and with list structures as a very flexible basic data type; pro- grams are themselves list structures, and thus can be created and manipulated just like other data. This introduction isn't intended to give you all the details, but just enough to get across the essential ideas, and to let you get under way quickly. The best way to make use of it is in front of a computer, trying out all the things mentioned. Basic characteristics of Lisp and Common Lisp: • Lisp is primarily intended for manipulating symbolic data in the form of list struc- tures, e.g., (THREE (BLIND MICE) SEE (HOW (THEY RUN)) !) • Arithmetic is included, e.g., (SQRT (+ (* 3 3) (* 4 4))) or (sqrt (+ (* 3 3) (* 4 4))) (Common Lisp is case-insensitive, except in strings between quotes " ... ", specially delimited symbols like |Very Unusual Symbol!|, and for characters prefixed with \\"). • Common Lisp (unlike John McCarthy's original \pure" Lisp) has arrays and record structures; this leads to more understandable and efficient code, much as in typed languages, but there is no obligatory typing. • All computation consists of expression evaluation. For instance, typing in the above (SQRT ...) expression and hitting the enter key immediately gives 5. • Lisp is a functional language based on Alonzo Church's λ-calculus (which like Turing machines provides a complete basis for all computable functions). For instance, a function for the square root of the sum of two squares can be expressed as (lambda (x y) (sqrt (+ (* x x) (* y y)))).