cond-expressions are two
examples of control structures in Scheme -- expressions that
control the order in which their subexpressions are evaluated or the
circumstances under which they are evaluated. Scheme provides two other
control structures that do conditional evaluation: the
and-expression and the
and-expression, the expressions that follow the keyword
and are evaluated in succession until one is found to have the
#f (in which case the rest of the expressions are
skipped and the
#f becomes the value of the entire
and-expression) or all of the expressions have been evaluated
(in which case the value of the last expression becomes the value of the
and-expression). This gives the programmer a way to combine
several tests into one that will succeed only if all of its parts succeed.
or-expression, the expressions that follow the keyword
or are evaluated in succession until one is found to have a
value other than
#f (in which case the rest of the expressions
are skipped and this value becomes the value of the entire
or-expression) or all of the expressions have been evaluated
(the value of the
gives the programmer a way to combine several tests into one that will
succeed if any of its parts succeeds.
Wednesday, 6 September 2000
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This page may be found at http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2000F/Readings/andor.html
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