Vaughan is an F# implementation of a generic Top-Down-Operator-Precedence Parser as described in this paper, it borrows it's name from the algorithms original inventor Vaughan Pratt.
It has been extended to allow for statements in comparison to Pratt's original algorithm which only parsed languages which use expression-only grammar.
The parser is "impure" in the sense that is uses a ref-cell for storing the input in the T<_, _, _> record class, this is soley for performance reasons as it's to expensive to create a new record object for every consumed token. Certain functions also throw exceptions, which generally also is considered impure.
Pretty printed error messages are produced, such as:
Error on line: 5 col: 9
4: if(x == y) {
5: print'x equals y');
----------^
Unexpected: #string "x equals y"