Programa de P?s-Gradua??o em Ci?ncia da Computa??o. Departamento de Ci?ncia da Computa??o, Instituto de Ci?ncias Exatas e Biol?gicas, Universidade Federal de Ouro Preto.Parsing is pervasive in computing and fundamental in several software artifacts. This
dissertation reports the rst step in our ultimate goal: a formally veri ed toolset for
parsing regular and context free languages based on derivatives. Speci cally, we describe
the formalization of Brzozowski and Antimirov derivative based algorithms for regular
expression parsing, in the dependently typed language Agda. The formalization produces
a proof that either an input string matches a given regular expression or that no matching
exists. A tool for regular expression based search in the style of the well known GNU
Grep has been developed using the certi ed algorithms. Practical experiments conducted
using this tool are reported
