FP84 is an extension of John Backus

John Backus

John Warner Backus was an American computer scientist. He directed the team that invented the first widely used high-level programming language and was the inventor of the Backus-Naur form , the almost universally used notation to define formal language syntax.He also did research in...

' FP programming language

FP programming language

FP is a programming language created by John Backus to support the function-level programming paradigm...

 to include infinite sequences, programmer-defined combining forms (analogous to those that Backus himself added to FL

FL programming language

FL is a programming language created at the IBM Almaden Research Center by John Backus, John Williams, and Edward Wimmers in 1989....

, his successor to FP), and lazy evaluation

Lazy evaluation

In programming language theory, lazy evaluation or call-by-need is an evaluation strategy which delays the evaluation of an expression until the value of this is actually required and which also avoids repeated evaluations...

.

Unlike FFP, another one of Backus' own variations on FP, FP84 makes a clear distinction between objects and functions: i.e., the latter are no longer represented by sequences of the former.

FP84's extensions are accomplished by removing the FP restriction that sequence construction be applied only to non-⊥ objects: in FP84 the entire universe of expressions (including those whose meaning is ⊥) is closed under sequence construction.

FP84's semantics is embodied in an underlying algebra of programs, this is, a set of function-level

Function-level programming

In computer science, function-level programming refers to one of the two contrasting programming paradigms identified by John Backus in his work on programs as mathematical objects, the other being value-level programming....

equalities that may be used to manipulate and to reason about programs.