The treatment of data types in EL1
Communications of the ACM
PASCAL user manual and report
The System Language for Project SUE
Proceedings of the SIGPLAN symposium on Languages for system implementation
The impact of language design on the production of reliable software
Proceedings of the international conference on Reliable software
An assessment of the programming language PASCAL
Proceedings of the international conference on Reliable software
The SNOBOL 4 programming language
The SNOBOL 4 programming language
The external consistency of abstract data types
ACM SIGPLAN Notices
Structured Specification of Communicating Systems
IEEE Transactions on Computers
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When defining a data type, it is often useful to specify restrictions on the permitted values of that type. Pascal's subrange type declaration, a special case of this kind of constraint definition, has already proved itself to be quite useful. Restricted data types allow more complex constraints to be defined and checked; for example, a variable could be declared of type “odd integer” or the day field of a “date” type variable could be checked for consistency with the year and month fields. A simple mechanism is proposed, allowing the formulation of such constraints and their association with data types; the behaviour of a restricted type variable is described. The effects of the use of such a mechanism on program reliability, readability and efficiency are discussed.