1.2 Mode Spec
When describing a predicate, we present its usage with a mode
spec, which has the form name(arg, ..., arg), where each
arg denotes how that argument is used by the predicate, and has
one of the following forms:
- The argument is used as a term denoting a goal or a clause or a predicate
name, or that otherwise needs special handling of module prefixes. It
is is subject to module name expansion (see ref-mod-mne).
- The argument is an input argument. Usually, but not always, this
implies that the argument should be instantiated.
- The argument is an output argument. Usually, but not always, this
implies that the argument should be uninstantiated.
- The argument may be used for both input and output.
Please note: The reference pages for built-in predicate use
slightly different mode specs.
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