CS 614: Theory and
Construction of Compilers
Lecture 5
Fall 2003
Department of
Computer Science
University of Alabama
Joel Jones
Introduction to Lexing Tools
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C is action language
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lex
flex
Java is action language
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Jlex
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Lexing Tool Basics
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Translate lexing specification to program
Regular expressions
Action code
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Regular Expressions
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. 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
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^ 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)
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| 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
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Digit
Integer
Optional Unary Minus
Decimal Numbers
(0.0, 4.5, but not 0 or
2, or unary minus)
Decimal Numbers (no
unary minus)
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Decimal Numbers
(with unary minus)
Float style exponent
(just the exponent, ‘e’
or ‘E’, optionally
signed)
Complete Real
number
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JLex Structure
n
n
n
n
n
user code
%%
JLex directives
%%
regular expression rules
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Reading & Questions for Next
Class
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JLex webpages
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Home Page
• http://www.cs.princeton.edu/~appel/modern/java/JLex/
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Tutorial
• http://bmrc.berkeley.edu/courseware/cs164/fall99/
assignment/a1/tutorial.html
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