| sentence | ::= module : sentence
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| | list | { where list is a list of sentence }
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| | clause
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| | directive
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| | query
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| | grammar-rule
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|
| clause | ::= rule | unit-clause
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|
| rule | ::= head :- body
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| unit-clause | ::= head | { where head is not otherwise a sentence }
|
|
| directive | ::= :- body
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|
| query | ::= ?- body
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| head | ::= module : head
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| | goal | { where goal is not a variable }
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|
| body | ::= module : body
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| | body -> body ; body
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| | body -> body
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| | \+ body
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| | body ; body
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| | body , body
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| | goal
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| goal | ::= term | { where term is not otherwise a body }
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|
| grammar-rule | ::= gr-head --> gr-body
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|
| gr-head | ::= module : gr-head
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| | gr-head , terminals
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| | non-terminal | { where non-terminal is not a variable }
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|
| gr-body | ::= module : gr-body
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| | gr-body -> gr-body ; gr-body
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| | gr-body -> gr-body
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| | \+ gr-body
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| | gr-body ; gr-body
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| | gr-body , gr-body
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| | non-terminal
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| | terminals
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| | gr-condition
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| non-terminal | ::= term | { where term is not otherwise a gr-body }
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|
| terminals | ::= list | string
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|
| gr-condition | ::= ! | {body}
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| module | ::= atom
|