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grammar-lower.rkt
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grammar-lower.rkt
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#lang racket
(define (lower-grammar g)
(cons 'parser-syntax
(append-map lower-rule (rest g))))
(define (lower-rule rule)
(match rule
[(list 'rule rule-name
(list 'alteration a1 ...
(list 'expansion
x ...
(list type name maybe-star ... "?")
y ...)
a2 ...))
(lower-rule
`(rule ,rule-name
(alteration ,@a1
(expansion ,@x (,type ,name ,@maybe-star) ,@y)
(expansion ,@x ,@y)
,@a2)))]
[(list 'rule rule-name
(list 'alteration a1 ...
(list 'expansion
x ...
(list type name "*")
y ...)
a2 ...))
(cons `(rule ,(string-append name "*")
(alteration (expansion (,type ,name) (non-terminal ,(string-append name "*")))
(expansion)))
(lower-rule `(rule ,rule-name
(alteration ,@a1
(expansion ,@x (non-terminal ,(string-append name "*")) ,@y)
,@a2))))]
[_ (list rule)]))
(provide lower-grammar)
(module+ test
(require rackunit)
(define-syntax-rule (check-lower? got should)
(check-equal? (lower-grammar (cons 'parser-syntax got))
(cons 'parser-syntax should)))
(check-lower?
'((rule "a"
(alteration
(expansion (non-terminal "prea")
(terminal "b" "?")
(non-terminal "c")))))
'((rule "a"
(alteration
(expansion (non-terminal "prea")
(terminal "b")
(non-terminal "c"))
(expansion (non-terminal "prea")
(non-terminal "c"))))))
(check-lower?
'((rule "NP"
(alteration
(expansion (terminal "determiner")
(terminal "adjective" "*")
(terminal "noun")))))
'((rule "adjective*"
(alteration (expansion (terminal "adjective")
(non-terminal "adjective*"))
(expansion)))
(rule "NP"
(alteration (expansion (terminal "determiner")
(non-terminal "adjective*")
(terminal "noun"))))))
(check-lower?
'((rule "a"
(alteration
(expansion (non-terminal "prea")
(non-terminal "b" "?")
(non-terminal "c")))))
'((rule "a"
(alteration
(expansion (non-terminal "prea")
(non-terminal "b")
(non-terminal "c"))
(expansion (non-terminal "prea")
(non-terminal "c"))))))
(check-lower?
'((rule "NP"
(alteration
(expansion (terminal "determiner")
(non-terminal "adjective" "*")
(terminal "noun")))))
'((rule "adjective*"
(alteration (expansion (non-terminal "adjective")
(non-terminal "adjective*"))
(expansion)))
(rule "NP"
(alteration (expansion (terminal "determiner")
(non-terminal "adjective*")
(terminal "noun"))))))
(check-lower?
'((rule "NP"
(alteration (expansion (terminal "determiner" "?")
(terminal "adjective" "*")
(terminal "noun")))))
'((rule "adjective*"
(alteration (expansion (terminal "adjective")
(non-terminal "adjective*"))
(expansion)))
(rule "adjective*"
(alteration (expansion (terminal "adjective")
(non-terminal "adjective*"))
(expansion)))
(rule "NP"
(alteration (expansion (terminal "determiner")
(non-terminal "adjective*")
(terminal "noun"))
(expansion (non-terminal "adjective*")
(terminal "noun"))))))
(check-lower?
'((rule "a"
(alteration
(expansion (non-terminal "prea")
(terminal "b" "*" "?")
(non-terminal "c")))))
'((rule "b*"
(alteration
(expansion (terminal "b")
(non-terminal "b*"))
(expansion)))
(rule "a"
(alteration
(expansion (non-terminal "prea")
(non-terminal "b*")
(non-terminal "c"))
(expansion (non-terminal "prea")
(non-terminal "c")))))))