Unicon Language Reference Clinton L. Jeffery Shamim Mohamed ...

3.6 File
Files are system resources corresponding to data on secondary storage, areas on users’ displays,
network connections, or databases. Operations on files cause input or output side effects on the
system outside of the program execution.
4 Variables
Variables are names for locations in memory where values can be stored. Values are stored in
variables by assignment operators. A variable name begins with a letter or underscore, followed
by zero or more letters, underscores, or digits. A variable name cannot be the same as one of
Icon’s reserved words, nor can it be the same as one of Icon’s keywords if it follows an adjacent
ampersand character. Variables can hold values of any type, and may hold different types of
values at different times during program execution.
There are four kinds of variables: global, local, static, and class. Global, local, and static
variables are declared by introducing one of the reserved words (global, local, or static) followed by
a comma-separated list of variable names. Global variables are declared outside of any procedure
or method body, while local and static variables are declared at the beginning of procedure and
method bodies. Local and static variable names may be followed by an assignment operator and
an initial value; otherwise variables other than procedure and class names begin with the value
&null.
Aliasing occurs when two or more variables refer to the same value, such that operations on
one variable might affect the other. Aliasing is a common source of program bugs. Variables
holding integer, real, string, or cset values are never aliased, because those types are immutable.
4.1 Global
Global variables are visible everywhere in the program, and exist at the same location for the entire
program execution. Declaring a procedure declares a global variable initialized to the procedure
value that corresponds to the code for that procedure.
4.2 Local
Local variables exist and are visible within a single procedure or method only for the duration of a
single procedure invocation, including suspensions and resumptions, until the procedure returns,
fails, or is vanquished by the return or failure of an ancestor invocation while it is suspended.
Undeclared variables in any scope are implicitly local, but this dangerous practice should be
avoided in large programs.
Variables that are declared as parameters are local variables that are preinitialized to the
values of actual parameters at the time of a procedure or method invocation. The semantics of
parameter passing are the same as those of assignment.
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