Revised(5) Report on the Algorithmic Language Scheme - Naming conventions

### 1.3.5 Naming conventions

By convention, the names of procedures that always return a boolean value usually end in "?". Such procedures are called predicates.

By convention, the names of procedures that store values into previously allocated locations (see section 3.4) usually end in "!". Such procedures are called mutation procedures. By convention, the value returned by a mutation procedure is unspecified.

By convention, "->" appears within the names of procedures that take an object of one type and return an analogous object of another type. For example, list->vector takes a list and returns a vector whose elements are the same as those of the list.