# CPL (programming language)

Paradigm procedural, imperative, structured, functional Christopher Strachey et al. 1963 ALGOL 60 BCPL, POP-2

CPL (from Combined Programming Language and Cambridge Programming Language before that) is a multi-paradigm programming language, that was developed in the early 1960s.

## Design

Combined Programming Language (CPL)[1] was developed jointly between the Mathematical Laboratory at the University of Cambridge and the University of London Computer Unit during the 1960s hence CPL gained the nickname "Cambridge Plus London".[2] The collaborative effort was responsible for the "Combined" in the name of the language (previously, the name was Cambridge Programming Language). Christopher Strachey and David Barron were involved (for others see paper). In 1963 (when the paper was published) it was concurrently being implemented on the Titan Computer at Cambridge and the Atlas Computer at London.

It was heavily influenced by ALGOL 60, but instead of being extremely small, elegant and simple, CPL was intended for a wider application area than scientific calculations and was therefore much more complex and not as elegant as ALGOL 60. CPL was a big language for its time. CPL attempted to go beyond ALGOL to include industrial process control, business data processing and possibly some early command line games. CPL was intended to allow low-level programming and high level abstractions using the same language.

However, CPL was only implemented very slowly. The first CPL compiler was probably written about 1970,[3] but the language never gained much popularity and seems to have disappeared without trace sometime in the 1970s.

BCPL (for "Basic CPL", although originally "Bootstrap CPL"), was a much simpler language based on CPL intended primarily as a systems programming language, particularly for writing compilers; it was first implemented in 1967, prior to CPL's first implementation. BCPL then led, via B, to the popular and influential C programming language.

## Example

The function MAX as formulated by Peter Norvig:[3]

```Max(Items, ValueFunction) = value of
§ (Best, BestVal) = (NIL, -∞)
while Items do §
if Val > BestVal then (Best, BestVal) := (Item, Val)
Items := Rest(Items) §⃒
result is Best §⃒
```

(The closing symbol to match the opening symbol "§" is a "§" with a vertical stroke through it. That symbol can be composed in Unicode as "§⃒", which is § (U+00A7, SECTION SIGN) composed with ⃒ (U+20D2, COMBINING LONG VERTICAL LINE OVERLAY), but it may not display correctly on your browser.)