Creating AST out of an arithmetic expression supporting addition and subtraction
Creating AST out of elementary expression with/without parentheses
Added AST-examples to description
Added expression parser from Scala for the Impatient by Cay Horstmann.

This parser demonstrate that you have to be careful whether an operation is left- or right-associative when designing your grammar.
Expression parser supporting power with ^ operator (both arith and AST variant)
Using non-back-tracking sequential composition operator
Updated doc
Shorter class names
Added BetterErrMsgExprEvaluator
Solution to exercise 3 of Scala for the Impatient
Calculator supporting variables and assignments using a mutable map
Improved Scaladoc
Cross-ref in Scaladoc to parser combinator configuration language
Using OneInstancePerTest instead of clearing the vars
Looked into a question at stackoverflow related to parser combinators