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19 lines
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Plaintext
19 lines
1.0 KiB
Plaintext
created: 20150105133800000
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modified: 20211117212441252
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tags: Concepts
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title: Railroad Diagrams
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<<.def "Railroad diagrams">>, sometimes called <<.def "syntax diagrams">>, are a visual way of explaining the syntax rules of a computer language. Reading one is like reading a public transport map.
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Each diagram starts on the left and ends on the right. Simply follow any line from the startpoint to the endpoint. All the alternative lines are equally valid. A line will sometimes jump over an item that is optional, or loop back to indicate that an item can be repeated.
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<$railroad text="""
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start [:optional] {repeated +","} end
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"""/>
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In the example above, a comma appears between each occurrence of the `repeated` item. The comma path runs from right to left, and can only be reached by first passing through `repeated`.
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Characters in round boxes are literal, i.e. they denote themselves. A name in a rectangular box denotes a further railroad diagram.
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The railroad diagrams in ~TiddlyWiki's documentation are generated with the [[Railroad Plugin]].
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