24 lines
1.2 KiB
Plaintext
24 lines
1.2 KiB
Plaintext
created: 20140210141217955
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list: [[Filter Expression]] [[Filter Run]] [[Filter Step]] [[Filter Parameter]] [[Filter Whitespace]]
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modified: 20230710074340943
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tags: Filters
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title: Filter Syntax
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type: text/vnd.tiddlywiki
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<<.preamble """[[Filters]] follow a grammar that is presented here, using [[railroad diagrams|Railroad Diagrams]], for those who find formal syntax descriptions helpful. However, you can [[learn to write filters|Introduction to filter notation]] without needing to understand this group of tiddlers.""">>
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A <<.def filter>> is a pipeline for transforming an <<.def input>> into an <<.def output>>. Both the input and the output are [[ordered sets of titles|Title Selection]] of tiddlers and fields.
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Filters are ''expressions'' constructed from smaller building blocks, called ''runs'', which are built using ''steps''. Eeach of which also transforms an input to an output.
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A filter starts with an empty output. Its runs are processed from left to right, progressively modifying the output.
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The "Filter Syntax" description starts with:
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<$railroad text="""
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\start double
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\end double
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[[<"Filter Expression">|"Filter Expression"]]
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"""/>
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<<.tip "The railroad boxes as the one above can be used to navigate">> |