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Unit 8: Programming Language: Types and Functions

• Depending on the language, signals normally cause a user-provided routine to be called,
smack in the middle of everything. Exceptions can be reduced to signals, but this is inelegant. Notes
• An exception handler is attached to some unit, and is executed instead of the remainder of the
unit when an exception occurs.
• Program holds module which contain routines which consist of blocks.
• Distinguish blocks, scopes and visibility ranges.
• There is no fundamental difference between functions and operators: operators are a special
case of functions and functions are a special case of operators.
• Just as we have anonymous integer values or anonymous array values, we can have anony-
mous routine values.
• A module is like a record in that it provides a syntactic scope the names in which can be
known outside that scope.
• Specification modules: Contain the information needed by user and compiler to use the items
declared in the module. Implementation modules: contain the rest which compiled once and
stored in a library.
• A module contains a data type with its routines. An abstract data type is a data type and
contains its routines as some of its fields.
• A generic item is a template from which one or more items can be created at compile time
through instantiation. This template has parameters, typed with a generic type. A generic
type is not restricted to data types and can include such things as data type names, macro
names, etc.
• In Icon, an expression yields a result and a suspended expression; the latter is invisible to the
user, but is used by the system to obtain further results if the present result causes failure of
some sort.
• Icon is very suitable for search and combinatorial problems.
• Prolog uses a stack rather than local and formal variables to store and pass data.

Imperative languages are procedural, command-driven or statement oriented
languages. e.g., C, C++, FORTRAN, ALGOL, Ada, Pascal, Smalltalk. Support this model.

8.6.2 Object-Oriented Languages

• Object-orientation = abstract data type + inheritance + dynamic binding.
• Abstract data type = all info on the data is included in the type: constants, variables, access
methods (procedures and functions). The variables are usually hidden form the user; access
to them is through the access methods only.
• Inheritance = type extension.
• The idea behind object-Oriented Programming, (OOP) is that a computer program may be
seen as comprising a collection of individual units or objects that act on each other.
• Each object is capable of receiving messages, processing data and sending messages to other
objects.
• OOP is claimed to promote greater flexibility and maintainability in programming.
• Some languages like C++, Java, smalltalk etc support this model.

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