ISWIM

ISWIM is an abstract programming language designed by Peter Landin and introduced in his 1966 article The Next 700 Programming Languages, published in Communications of the ACM. It combines imperative and functional programming, built around a functional core that presents itself as a kind of syntactic sugaring of the lambda calculus, extended with mutable variables and assignment. ISWIM was never directly implemented as a working system, but its design profoundly shaped later functional language development, influencing languages including SASL, Miranda, ML, Haskell and Clean, and it also affected dataflow languages such as Lucid. Descendants of ISWIM's ideas split along two lines, some retaining its imperative features, as ML did alongside its type inference, and others stripping them away entirely to build purely functional languages based on lazy evaluation.