In computer science, a Pratt parser is an improved recursive descent parser that associates semantics with tokens instead of grammar rules.[1] It was first described by Vaughan Pratt in the 1973 paper "Top down operator precedence"[2], and was treated in much more depth in a Masters Thesis under his supervision[3]. Pratt designed the parser originally to implement the CGOL programming language. Douglas Crockford used the technique to build JSLint.