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defines as shorthand for .
As a consequence, if you write e.g.
then that will macro expand to
which in turn macro expands to
which in turn defines the value aspect of the factorial function.
The construct is for feinschmeckers; it disappears during macro expansion but guarantees that the principal operator of the term is not macro expanded. The protection is only needed when one gives both a macro and a value definition for the same term.
The construct is easy to use but of limited power. It just cause the left hand side to be replaced by the right hand side.
The base page macro defines parentheses thus:
Thus, parentheses disappear during macro expansion (unless protected by some other macro construct like ).
Macro expansion occurs inside Gödel brackets. As an example,
is true because the parenthesis disappears during macro expansion in the first bracket and because the preassociativity of plus ensures that the term in the second bracket ends up having the same structure as the term in the first bracket.
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