II. Notes on Data Structuring * - Cornell University

148 c.A.R. HOARE
end;
p: = compile primary;
fs: = [factor (times, p)];
while source.first = times v source.first - div do
begin sign from source;
end;
p: = compile primary;
fs" [factor (sign, p)]
compile term: = term (s, fs)
function compile primary: primary;
begin s" symbol;
end;
s from source;
with s do (constant:compile primary:= const (value),
variable" compile primary'= var (identifier),
leftbracket:
begin from source;
compile primary'= bracketed (compile expression);
s from source;
if s g: rightbracket then go to error
end,
else go to error }
Exercise
Write programs to convert an expression from tree representation to
bitstream and back again.
10. SPARSE DATA STRUCTURES
In dealing with representations of arrays and powersets, we have hitherto
assumed that the base type of a powerset and the domain type of an array is
reasonably small, so that it is possible to allocate a bit or larger area of store
to hold the value of every potential element of the structure. The examples
also were confined to such cases. In this chapter we investigate the conse-
quences and problems which arise when the base or domain types are very
large or infinite, and when the standard representations are therefore
impossible.