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6th
When Is A Functional Program Not A Functional Program?
John Longley. ICFP 1999. In an impure functional language, there are programs whose behavior is completely functional (in that they behave extensionally on inputs) but the functions they compute cannot be written in the purely functional fragment of the language. That is, the class of programs with functional behavior is more expressive than the usual class of pure functional programs. In this paper we introduce this extended class of “functional” programs by means of examples in Standard ML, and explore what they might have to offer to programmers and language implementors.