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Euler is a programming language created by Niklaus Wirth and Helmut Weber, conceived as an extension and generalization of ALGOL 60. The designers' goal was to create a language:

• which was simpler, and yet more flexible, than ALGOL 60
• that was a useful programming language processed with reasonable efficiency
• that can be defined with rigorous formality

Euler employs a general type concept. In Euler, arrays, procedures and switches are not quantities which are declared and named by identifiers: they are not (as opposed to ALGOL) quantities which are on the same level as variables, rather, these quantities are on the level of numeric and boolean constants. Thus, besides the traditional numeric and logical constants, Euler introduces the following additional types:

• reference
• label
• symbol
• list (array)
• procedure
• undefined

All constants can be assigned to variables, which have the same form as in ALGOL, but for which no fixed types are specified: Euler is a dynamically typed programming language. Furthermore, a procedure can produce a value of any type when executed, and this type can vary from one call of the procedure to the next. Similarly, the elements of a list can have values of any type and these can be different from element to element within the list. So, when the list elements are labels, a switch is obtained. If the elements are procedures, a producedure list is obtained (which is not available in ALGOL 60). If the elements are lists themselves, then a general tree structure obtains. Euler provides general type-test and type-conversion operators.