Stanford University: Keith Schwarz's "Lexical Analysis"

Read pages 1 - 10. Formal languages are defined by formal grammars. Regular and context-free grammars are applied in scanning and parsing of programming languages. Formal grammars define the syntax of a formal language.

Click http://web.archive.org/web/20160310180534/http://www.keithschwarz.com/cs143/WWW/sum2011/handouts/030_Lexical_Analysis.pdf link to open resource.