Annotated edit history of
ReversePolish version 8, including all changes.
View license author blame.
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AristotlePagaltzis |
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Styles of syntax used for writing expressions or tree-structured data: |
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!!!Infix |
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In infix notation you write the operator between the arguments: |
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c - (5 + a + x) * b |
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Infix notation is the usual. It needs precedence rules and/or brackets to make the order of operations unambiguous. Polish and Reverse Polish don't have that problem, providing the number arguments to each operator is fixed. |
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!!!Reverse Polish |
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In Reverse Polish, or __postfix__, notation you write the operator after the arguments. |
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c 5 a + x + b * - |
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JohnMcPherson |
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It's very easy to interpret expressions in this notation, you need just a single stack to place intermediate values on, this is why [Forth] and PostScript (which was based on Forth?) use it. |
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AristotlePagaltzis |
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!!!Polish |
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In Polish, or __prefix__, notation you write the operator before the arguments. |
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- c * + 5 + a x b |
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Polish notation is called that because a famous Polish mathematician first used it for Boolean algebra, and nobody can either remember or pronounce his name without looking it up first. (''You'' go look it up.) |
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!!!S-expressions |
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In S-expression, or [LISP], notation you write the operator before the arguments, enclosed in brackets: |
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(- c (* (+ 5 a x) b)) |
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[LISP] operators take any number of arguments so [LISP] expressions need brackets to associate arguments with operators. |
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It's very easy to parse this notation into tree structures, which is why [LISP] uses it. |
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!!!XML |
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In XML notation you bracket the arguments with the operator: |
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<subtract> |
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<variable name="c"/> |
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<multiply> |
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<add> |
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<constant value="5"/> |
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<variable name="a"/> |
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<variable name="x"/> |
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</add> |
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<variable name="b"/> |
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</multiply> |
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</subtract> |
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Whoever came up with this had good intentions, I'm sure... |
