The left hand side

The left hand side of rewriting rules contains a pattern. Normal words are simply matched directly. Metasyntax is introduced using a dollar sign. The metasymbols are:


$* Match zero or more tokens
$+ Match one or more tokens
$- Match exactly one token
$=x Match any phrase in class x
$~x Match any word not in class x
If any of these match, they are assigned to the symbol $ n for replacement on the right hand side, where n is the index in the LHS. For example, if the LHS:
$-:$+
is applied to the input:
UCBARPA:eric
the rule will match, and the values passed to the RHS will be:

$1 UCBARPA
$2 eric

Additionally, the LHS can include $@ to match zero tokens. This is not bound to a $ n on the RHS, and is normally only used when it stands alone in order to match the null input.


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Last modified: Friday April 02, 1999.