FL (short for Function Level) is a programming language created at the IBM Almaden Research Center by John Backus, John Williams, and Edward Wimmers in 1989.
FL was designed as a successor of Backus' earlier FP language, providing specific support for what Backus termed function-level programming.
FL is a dynamically typed strict functional programming language with throw and catch exception semantics much like in ML. Each function has an implicit history argument which is used for doing things like strictly functional input/output (I/O), but is also used for linking to C code. For doing optimization, there exists a type-system which is an extension of Hindley–Milner type inference.
Many of the language’s innovative, arguably important ideas have now been implemented in Kenneth E. Iverson’s J language.