17.3 Quoted Expressions

Because symbolic evaluation requires that each variable or expression has a value, it is necessary to add to REDUCE the concept of a quoted expression by analogy with the Lisp QUOTE function. This is provided by the single quote mark . For example,

’a     represents the Lisp S-expression(quote a)
’(a b c)    represents the Lisp S-expression(quote (a b c))

Note, however, that strings are constants and therefore evaluate to themselves in symbolic mode. Thus, to print the string ~A String~, one would write

        prin2 ~A String~;

Within a quoted expression, identifier syntax rules are those of REDUCE. Thus (A !. B) is the list consisting of the three elements A, ., and B, whereas (A . B) is the dotted pair of A and B.