There is a general but fallacious impression that dynamically typed languages like Lisp are more appropriate for prototyping because it is “easy” to modify Lisp programs. The reason this impression is false is that serious prototypes can be large and complex programs, and if one changes the representation of data in one part of the prototype it can be a long, error-prone, and labor intensive process to trace all the consequences of such changes when using a dynamically typed language.
Reflections on Standard ML – David B. MacQueen