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\line{{\bf Subrange Types.} (See Standard Pascal, pp.\ 101--102.)\hfill}
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If $T$ is any ordinal type, and $A$ and $B$ are constants of type~$T$,
with $A≤B$, then $A\ldt B$ is an ordinal type, consisting of the values
of $T$ lying between $A$ and~$B$, inclusive; we call $A\ldt B$
a~{\sl subrange type\/} and $T$ its {\sl host type\/}. For example,
{\tt 1..10} is the subrange type consisting of the integers from one
to ten; {\tt 'A'..'D'} is the subrange type consisting of the first
four letters of the alphabet.

Values of a subrange type are values of the host type, and may be used
freely as such. Assignments to a variable of a subrange type are errors 
unless the value assigned belongs to the subrange, but are otherwise
like assignments to a variable of the host type.

Subrange types allow conservation of storage space for variables,
and automatic checking that values stay in a specified range.

[Examples?]


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\copyright 1984 Robert W. Floyd

First draft September 24, 1984

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