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→Example: add notes and examples
| accessdate = 2012-04-22
| accessdate = 2012-04-22
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''Expression'' -> ''Term'' # an ''Expression'' is either a ''Term''
''Expression'' -> ''Term'' # an ''Expression'' is either a ''Term''
''AddSubOp'' -> '''+'''. '''-''' # addition and subtraction have the same priority
''AddSubOp'' -> '''+'''. '''-''' # addition and subtraction have the same priority
''Number'' -> '''0''', '''1''', ... '''9''' # this simple-minded definition of a ''Number'' is enough for this example
''Number'' -> '''0''', '''1''', ... '''9''' # this simple-minded definition of a ''Number'' is enough for this example
Notes:
* Both ''Expression'' and ''Term'' are each defined via a left-recursive rule; this ensures that operators of the same priority are applied from left to right.
* The distinction between ''Expression'' and ''Term'' ensures that multiplication/division are applied before addition/subtraction.
* ''Expression'' is indirectly recursive via ''Term'' and ''Primary'' to allow bracketed sub-expressions to any depth.
Example 1: generate 2 + 3 * 4
''Expression'' -> ''Expression'' ''AddSubOp'' ''Term''
-> ''Term'' ''AddSubOp'' ''Term''
-> ''Primary'' ''AddSubOp'' ''Term''
-> '''2''' '''+''' ''Term'' # '''+''' can not be applied until ''Term'' has been evaluated
-> '''2''' '''+''' ''Term'' ''MulDivOp'' ''Primary''
-> '''2''' '''+''' ''Primary'' ''MulDipOp'' ''Primary''
-> '''2''' '''+''' '''3''' '''*''' '''4'''
Example 2: generate 2 * 3 + 4
''Expression'' -> ''Expression'' ''AddSubOp'' ''Term''
-> ''Term'' ''AddSubOp'' ''Term''
-> ''Term'' ''MulDivOp'' ''Primary'' ''AddSubOp'' ''Term''
-> ''Primary'' ''MulDivOp'' ''Primary'' ''AddSubOp'' ''Term''
-> '''2''' '''*''' '''3''' ''AddSubOp'' ''Term'' # ''Term'' to left of ''AddSubOp'' is evaluated first
-> '''2''' '''*''' '''3''' ''AddSubOp'' ''Primary''
-> '''2''' '''*''' '''3''' '''+''' '''4'''
===Level 1===
===Level 1===