30 lines
906 B
Factor
30 lines
906 B
Factor
! Copyright (C) 2008 Chris Double.
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! See http://factorcode.org/license.txt for BSD license.
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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)+ [[ unclip [ swap 10 * + ] reduce ]]
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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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;EBNF
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: eval-expr ( string -- number )
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expr parse-result-ast ;
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