Editing Euler (programming language) (section)

==Overview==
Euler employs a general [[data type]] concept. In Euler, [[Array data type|arrays]], [[Subroutine|procedures]], and switches are not quantities which are declared and named by identifiers: in contrast to [[ALGOL]], they are not quantities on the same level as [[Variable (computer science)|variables]]. Rather, these quantities are on the level of numeric and boolean [[Constant (computer programming)|constants]]. Thus, besides the traditional numeric and logical constants, Euler introduces several added types:
* Reference
* [[Label (programming language)|Label]]
* [[Symbol (programming)|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 uses [[dynamic typing]]. Further, 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 differ from element to element within a list. So, when the list elements are labels, a switch is obtained. If the elements are procedures, a procedure list is obtained, which is unavailable in ALGOL 60. If the elements are lists themselves, then a general tree structure is obtained.

Euler provides general type-test and type-conversion operators.