Editing NPL (programming language) (section)

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'''NPL''' is a [[Functional programming|functional programming language]] with [[pattern matching]] designed by [[Rod Burstall]] and [[John Darlington]] in 1977. The language allows certain sets and logic constructs to appear on the right hand side of definitions, e.g.

 setofeven(X) <= <:x: x in X & even(x) :>

The NPL interpreter evaluates the list of generators from left to right so conditions can mention any bound variables that occur to their left. These were known as [[set comprehension]]s. NPL eventually evolved into [[Hope programming language|Hope]] but lost set comprehensions, which made a reappearance in the form of [[list comprehension]]s in later functional languages.