[SOLVED] 代写 compiler Compiler Theory

Compiler Theory
Assignment 3, January 29, 2019
Regular Expressions

Reading: Chapter 3.3: Regular Expressions
Chapter 3.4: Finite State Automata
Chapter 3.5: From Regular Expressions to Finite State Automata

A “regular expression” is a string of characters that specifies a pattern that can
be test-matched to strings made up of characters from a given alphabet.Regular
expressions are constructed as follows:
Atomic expressions:
single character from the given alphabet:matches the character itself
e (epsilon)the empty string – matches a zero-length string
[a-z]character class; matches a single character in the range or ranges given
inside the square brackets, i.e. [a-zA-Z0-9] is one alphanumeric character.
Compound expressions (r and s are regular expressions here)
rs concatenation, r followed by s; matches a string matching r immediately
followed by a string matching s.
r|sr or s; matches a string matching r or matching s.
r* Kleene closure; matches the concatenation of zero or more strings
matching r; may be different strings.
r+ positive closure; matches the concatenation of one or mere strings
matching r; may be different strings.
(r)parentheses for controlling the order of operations.

Precedence: In the absence of parentheses, * and + have highest precedence, then
concatenation, then |.

Quoting: If the alphabet contains any of the characters that have special meaning
in regular expression syntax, such as | * + ( ) [ ] -, then those special
characters can be used as ordinary characters by quoting them, i.e. ‘+’.

Assignment:

Write regular expressions and draw finite state automata for the following
languages.The alphabet for all is {a,b,c}.Empty strings are legal unless
stated otherwise.A string is accepted if the statement is true about it,
regardless of what else is true about the string.

1. String contains exactly one a.( cabcc is ok, but not cabbac or bbcc )

2. String contains exactly two a’s. ( aa and babbca are ok, but not aaaa )

OVER

3. String contains an even number of a’s (zero counts as even).
( abaabba is ok, but not abccaabb )

4. The first b (if any) occurs before the first c (if any).
( aababbcab, aaacc, and abba are ok, but not aaacabcaa )

5. All b’s occur before all c’s.
( aababbaccaa, acca, and bba are ok, but not aacab or abcab )

6. The pair ab does not occur.
( acacba is ok, but notaacbcabb )