cs375 p. 45

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Regular Expressions

Regular expressions are a more convenient way (than a regular grammar) to specify a regular language. We will use lex conventions for specifying regular expressions. An expression is specified in left-to-right order.

Expression: Meaning:

[ chars ] Any member of the set of characters

chars .

[ c₁ - c₂ ] Any character from c₁ through c₂ .

[^ chars ] Any character except chars .

( specs ) Used to group specifications specs .

{ category } An instance of a previously named

category .

" string " Exactly the specified string .

s₁ | s₂ s₁ or s₂

spec * Zero or more repetitions of spec .

spec + One or more repetitions of spec .

spec ? Optional spec .

Expression:	Meaning:

`[` chars `]`	Any member of the set of characters
	chars .
`[` c₁ `-` c₂ `]`	Any character from c₁ through c₂ .
`[^` chars `]`	Any character except chars .
`(` specs `)`	Used to group specifications specs .
`{` category `}`	An instance of a previously named
	category .
`"` string `"`	Exactly the specified string .
s₁ `\|` s₂	s₁ or s₂
spec `*`	Zero or more repetitions of spec .
spec `+`	One or more repetitions of spec .
spec `?`	Optional spec .