Page "PostScript" Paragraph 38

PostScript is an interpreted, stack-based language similar to Forth but with strong dynamic typing, data structures inspired by those found in Lisp, scoped memory and, since language level 2, garbage collection.

The language syntax uses reverse Polish notation, which makes the order of operations unambiguous, but reading a program requires some practice, because one has to keep the layout of the stack in mind.

Most operators ( what other languages term functions ) take their arguments from the stack, and place their results onto the stack.

Literals ( for example, numbers ) have the effect of placing a copy of themselves on the stack.

Sophisticated data structures can be built on the array and dictionary types, but cannot be declared to the type system, which sees them all only as arrays and dictionaries, so any further typing discipline to be applied to such user-defined " types " is left to the code that implements them.