Use left recursive grammar in peg.expr
parent
af9e27823a
commit
d002e02948
extra/peg/expr
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@ -4,24 +4,19 @@ USING: kernel arrays strings math.parser sequences
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peg peg.ebnf peg.parsers memoize math ;
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IN: peg.expr
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: operator-fold ( lhs seq -- value )
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#! Perform a fold of a lhs, followed by a sequence of pairs being
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#! { operator rhs } in to a tree structure of the correct precedence.
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swap [ first2 swap call ] reduce ;
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EBNF: expr
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times = "*" [[ drop [ * ] ]]
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divide = "/" [[ drop [ / ] ]]
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add = "+" [[ drop [ + ] ]]
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subtract = "-" [[ drop [ - ] ]]
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digit = [0-9] => [[ digit> ]]
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number = (digit)+ => [[ 10 digits>integer ]]
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value = number
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| ("(" exp ")") => [[ second ]]
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digit = [0-9] [[ digit> ]]
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number = (digit)+ [[ unclip [ swap 10 * + ] reduce ]]
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fac = fac "*" value => [[ first3 nip * ]]
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| fac "/" value => [[ first3 nip / ]]
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| number
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value = number | ("(" expr ")") [[ second ]]
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product = (value ((times | divide) value)*) [[ first2 operator-fold ]]
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sum = (product ((add | subtract) product)*) [[ first2 operator-fold ]]
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expr = sum
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exp = exp "+" fac => [[ first3 nip + ]]
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| exp "-" fac => [[ first3 nip - ]]
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| fac
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;EBNF
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: eval-expr ( string -- number )
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