CS453 Colorado State University
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Regular Expressions and Transition Diagrams
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Logistics

    Tomorrow go to recitation 9-10 in 215

    Office hours and lab hours
        Wednesday at 2pm
        Monday at 2pm

    Should be done and TO DO next slides
    
    

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Goals for today

    - typical compiler and interpreter structure
    
    - overview of MeggyJava and MiniSVG
    
    - regular expressions and DFAs
    
    - transition diagrams
    

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Overview of a typical compiler and interpreter

    [rects for input and output files
     circles for things executing
    ]
    
    (draw) source program --> compiler --> target executable
    
    (draw) input --> target executable --> output
        
    -> how does this work with Java?
    
    [ 
        (draw)   source prog  -->  javac  -->  .class files  (bytecode)
        
        bytecode and input  --> JVM or java, an interpreter  --> output
     
        with JIT have just in time compilation in many JVMs
    ]

    
    
    -> specialized picture for MiniSVG interpreter
        (draw) file.svg --> MiniSVG interpreter --> text output and picture
    
    
    -> specialized picture for MeggyJava compiler
    
        (draw) 
        file.java --> MeggyJava compiler --> file.s
        file.s and MeggyJrSimple.o --> avr-g++ --> file.hex file
        file.hex file --> avrdude --> MeggyJr device
        

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Typical Structure of a Compiler

    (slide 5)

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MeggyJava compiler structure

    (slide 6 and 7)

    -> show fixed flower example
    
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MiniSVG interpreter structure

    (slide 8 thru 10)

    -> show project writeup from webpage, indicate link to download start code
    and instructions for how to compile and run
    
    The hardest part of this assignment is to implement the lexer.
        -> show transition diagram or DFA
        
    Today will learn regular expressions, DFAs, and transition diagrams, which
    are a kind of DFA.
    
    Tuesday will learn how to use regular expressions and transition diagrams
    to write a lexer for MiniSVG.

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Languages (slides 13-14)

    A language is a set of strings.
        Examples: 
            {aa, aaaa, aaaaaa, ... }    all strings with an even number of a's
            {while}                     the while keyword
            {while, for, do}            some loop keywords
            { <, >, ==, <>}             relational operators
            {Meggy.Color.RED, Meggy.Color.BLUE, ...}    colors for Meggy
            
    Empty string
    

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Regular Expressions

    Example regular expression (slide 15)
        -> note that concatenation of (b)(c) has higher precedence than
        alternation between a and (b)(c)
    
    Specifying regular expressions (slide 16)
    
        primitive regular expressions: empty set, epsilon, and alpha
            where alpha is any character and epsilon is the empty string
    
        -> empty set versus a set with the empty string, recall the 15min
        compiler example.  If language is an empty set, then even an
        empty file would result in a parse error.
    
        operations given regular expressions r1 and r2
            alternation, r1 | r2
            concatenation, (r1)(r2) or r1 r2
            kleene closure, r1^*
            parentheses, (r1)
            
    
    Regular expression examples and Regular definitions (slide 17)
        Keywords
            for, if, while, ...
            
        operations
            <, >, +, -, &&, ...
            
        Identifiers
            here is where it helps to have regular definitions
            letter = A | B | ... | Z | a | b | c | .... | z
                   = [A-Za-z]   // equivalent notation, character classes
                   
            digit = [0-9]
            
            [
             id = (letter | "_") (letter | "_" | digit)
            ]
            
        Numbers 
            

    We now know how to specify a regular language with regular expressions, but
    how do we determine if a string belongs to a specific language?


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Deterministic Finite Automata

    (slides 18-53)


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Transition Diagrams

    (slides 54-63)
    
    (slide 57)
    -> Note that with current transition diagram we will recognize 3 abba tokens
       even though there is no space between the first two.

    (slide 59)
    -> to force a space after each abba token and put in a white space
    transition with an asterisk to indicate backing up the pointer when
    create lexeme

TODO
    - post http://cs.oberlin.edu/~jdonalds/331/lecture04.html for extra reading
about transition diagrams

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mstrout@cs.colostate.edu, 1/20/11