# Formal Language and Parsing Constructs, Simplified¶

I fell down a Wikipedia rabbit-hole so you don't have to.

No knowldege is assumed besides a good grasp of programming and some basic set algebra.

You should read this page in order; some notation and concepts explained earlier are used further on.

This page remains under construction, and will likely never be complete.

`λ`

¶

(the lowercase Greek letter lambda)

One of two primary conventions to represent the empty string, and the one used on this page. (the other being epsilon)

## regex¶

An informal class of Regular Expressions; they exist in many

## Kleene Star¶

The Kleene Star , `some_set*`

, means "any element from this set, repeated zero or more times". For example, `{ab, c}*`

is `{λ, ab, c, abab, abc, cab, cc, abcc, ...}`

.

This is almost certainly the origin of the regex `*`

quantifier (`(ab|c)*`

matches `λ`

, `ab`

, `c`

, `abc`

, `cab`

, `cc`

, `abcc`

, etc.)

## Kleen Plus¶

The same as the Kleene Star, but not including `λ`

. It parallels the regex `+`

operator.

*First published: 2020-11-28 Last updated: 2020-11-28*