The design of procedural and object-oriented programming languages is considered with respect to how easily programs written in those languages can be formally manipulated. Current procedural languages such as Pascal, Modula-2 and Ada; generally support such program manipulations, except for some annoying anomalies and special cases. Three main areas of language design are identified as being of concern from a manipulation viewpoint: the interface between concrete and abstract syntax; the relationship between the abstract syntax and static semantics naming, scoping and typing; and the ability to express basic transformations (folding and unfolding). Design principles are suggested so that the problems identified for current languages can be avoided in the future.>