lecture04

# lecture04 - Written Assignments WA1 assigned today...

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1 Prof. Aiken CS 143 Lecture 4 1 Implementation of Lexical Analysis Lecture 4 Prof. Aiken CS 143 Lecture 4 2 Written Assignments • WA1 assigned today • Due in one week – By 5pm – Turn in • In class • In box outside 411 Gates • Electronically Prof. Aiken CS 143 Lecture 4 3 Tips on Building Large Systems • KISS (Keep It Simple, Stupid!) • Don’t optimize prematurely • Design systems that can be tested • It is easier to modify a working system than to get a system working Prof. Aiken CS 143 Lecture 4 4 Outline • Specifying lexical structure using regular expressions • Finite automata – Deterministic Finite Automata (DFAs) – Non-deterministic Finite Automata (NFAs) • Implementation of regular expressions RegExp => NFA => DFA => Tables Prof. Aiken CS 143 Lecture 4 5 Notation • There is variation in regular expression notation • Union: A | B A + B • Option: A + A? • Range: ‘a’+’b’+…+’z’ [a-z] • Excluded range: complement of [a-z] [^a-z] Prof. Aiken CS 143 Lecture 4 6 Regular Expressions in Lexical Specification • Last lecture: a specification for the predicate s L(R) • But a yes/no answer is not enough! • Instead: partition the input into tokens • We adapt regular expressions to this goal

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2 Prof. Aiken CS 143 Lecture 4 7 Regular Expressions => Lexical Spec. (1) 1. Write a rexp for the lexemes of each token Number = digit + Keyword = ‘if’ + ‘else’ + … Identifier = letter (letter + digit)* OpenPar = ‘(‘ Prof. Aiken CS 143 Lecture 4 8 Regular Expressions => Lexical Spec. (2) 2. Construct R , matching all lexemes for all tokens R = Keyword + Identifier + Number + … = R 1 + R 2 + … Prof. Aiken CS 143 Lecture 4 9 Regular Expressions => Lexical Spec. (3) 3. Let input be x 1 …x n For 1 i n check
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lecture04 - Written Assignments WA1 assigned today...

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