This thesis presents a design and partial implementation of a program family of extended pretty printers. Factors that influence the readability (perception) and understand ability (cognition) of computer programs are indentified, previous work is reviewed, and new solutions are suggested. Extensions to the previous pretty printer designs include a capability to selectively display levels of control of a program. In order to accommodate different computer languages and to allow for, several secondary functions, a family of pretty printers is designed. This design facilitates easy extension, contraction and modification.