30 lines
957 B
Factor
30 lines
957 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
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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" | "1" | "2" | "3" | "4" |
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"5" | "6" | "7" | "8" | "9"
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number = ((digit)+) [[ concat string>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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EBNF>
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: eval-expr ( string -- number )
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expr parse parse-result-ast ; |