CS 614: Theory and Construction of Compilers

Lecture 5Fall 2003Department of Computer ScienceUniversity of AlabamaJoel Jones

Lecture 5 ©2003 Joel Jones 2

Introduction to Lexing Tools C is action language

lex flex

Java is action language Jlex

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Lexing Tool Basics Translate lexing specification to program Regular expressions Action code

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Regular Expressions . Matches any single

character * Matches zero or more

copies of the preceding expression

[] Character class which matches any character within the brackets. If it starts with a circumflex ‘^’ negates test. A dash indicates a range

^ Matches the beginning of a line

$ Matches the end of a line \ escapes metacharacters e.g.

“\n” is a newline character, “\*” is a literal asterisk

+ Matches one or more occurrences

? Matches zero or one occurences

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Regular Expression (Continued) | Matches either the

regular expression before or after

“…” Interprets everything inside quotes literally

() Groups a series of regular expression together into a new regular expression

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Regular Expression Examples Digit Integer Optional Unary Minus Decimal Numbers

(0.0, 4.5, but not 0 or 2, or unary minus)

Decimal Numbers (no unary minus)

Decimal Numbers (with unary minus)

Float style exponent (just the exponent, ‘e’ or ‘E’, optionally signed)

Complete Real number

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JLex Structuren user coden %%n JLex directivesn %%n regular expression rules

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Reading & Questions for Next Class JLex webpages

Home Page• http://www.cs.princeton.edu/~appel/modern/java/JLex/

Tutorial• http://bmrc.berkeley.edu/courseware/cs164/fall99/assignment/a1/tutorial.html