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5d1c1eaf87
* Introduce let filter run prefix for assigning filter run result to a variable
* Get rid of the special behaviour for all[]
Not needed because the input to the filter run is available
* Fix tests
* Fix tests
* Cleanup
* Support for saving result lists in a variable
Extend let filter run prefix to store list of results, and add varlist operator for accessing variables as a list.
We already had partial support for variables returning a list of values in order for functions to work, now we extend it so that any variable can be used to store a list
We should extend the set widget so that it returns a result list that can be accessed with the varlist operator
* Docs update
* Introduce letlist widget for assigning lists to variables
Terrible name. Annoyingly, we can't overload the existing let or set widgets.
* Docs update
* Update DefaultTiddlers to highlight the new docs
* Fixed varlist crash with empty parameter
* Switch to triple brace syntax for assigning filtered lists
* Docs update
* Test for multivalued functions
* varlist operator: fixed crash accessing non-existent variable
See https://github.com/TiddlyWiki/TiddlyWiki5/pull/8972#issuecomment-2712068743
* Dispense with the letlist widget
What this PR actually does is rename the letlist widget to "let". The result is the same as using the letlist widget, but it is backwards compatible by virtue of the fact that all existing ways to access variables will only see the single value for the variable.
* Refactor the let filter run prefix to assign the input list to the variable named by the filter run
These semantics are much simpler, and allow the variable name to be computed.
* Missed off 211b135265
* Docs update
* Bug fix
* Introduce round brackets for multi-valued filter operands
Allowing us to drop the varlist operator
* Introduce => as a shortcut syntax for the let filter run prefix
Also relax the requirement for a filter run prefix to be followed by an opening square bracket
* Fix bug exposed in "Filter Operators" tiddler
See https://github.com/TiddlyWiki/TiddlyWiki5/pull/8972#issuecomment-2740003414
* Fix bug with missing variable attributes
See https://github.com/TiddlyWiki/TiddlyWiki5/pull/8972#issuecomment-2752792329
* Fix bug with round brackets for 2nd parameter onwards
* Allow functions to take multivalued parameters
* Simplify title operator
* Extend title operator to allow negated form to use multi-valued variables
* Remove duplicate test
* Update action-log widget to log multi-valued attributes
* Docs updates
* Fix typos
* Happy linter happy life
* Fix version numbers of from-version procedures
* Another incorrect version number
* Add change note
* Fix filenames of tests
* Typo
* Update let.js
* Docs updates
72 lines
3 KiB
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72 lines
3 KiB
Text
title: LetWidget
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created: 20211028115900000
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modified: 20250307212252946
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tags: Widgets
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caption: let
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! Introduction
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<<.from-version "5.2.1">> The <<.wid let>> widget allows more than one variable to be set in one operation. In some situations it can result in simpler code than using the more flexible <<.wlink SetWidget>> widget. It differs from the <<.wlink VarsWidget>> widget in that variables you're defining may depend on earlier variables defined within the same <<.wid let>>.
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! Content and Attributes
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The content of the <<.wid let>> widget is the scope for the value assigned to the variable.
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|!Attribute |!Description |
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|//{attributes}// |Each attribute name specifies a variable name. The attribute value is assigned to the variable |
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Attributes are evaluated in the order they are written. Attributes with the same name are allowed. Each time a duplicate attribute is encountered, it will replace the existing value set by the earlier duplicate.
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<<.note """<<.from-version "5.2.4">> There is no longer any restriction on using variable names that start with the $ character.""">>
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! Multi-Valued Variables
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<<.from-version "5.4.0">> The <<.wid let>> widget also allows [[multi-valued variables|Multi-Valued Variables]] to be set in one operation to the complete list of results obtained from evaluating an attribute.
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Almost all operations that work with variables only consider the first item in the list. Using round brackets instead of angle brackets around the variable name gives access to the complete list of results. For example:
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```
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<$let varname={{{ [all[tiddlers]sort[]] }}}>
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<$text text={{{ [(varname)] +[join[-]] }}}/>
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</$let>
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```
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! Examples
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Consider a case where you need to set multiple variables, where some depend on the evaluation of others.
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Using the <<.wid let>> widget, this situation may be handled in the following way:
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```
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\define helloworld() Hello world!
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<$let target="MyTiddler" currentTiddler={{{ [<target>prefix[$:/settings/for/]] }}} settings={{!!text}} currentTiddler=<<target>> >
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The settings for <<currentTiddler>> are: <<settings>>
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</$let>
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```
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In contrast, here is the same example using the <<.wid set>> widget:
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```
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<$set name="target" value="MyTiddler" >
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<$set name="currentTiddler" value={{{ [<target>prefix[$:/settings/for/]] }}} >
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<$set name="settings" value={{!!text}} >
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<$set name="currentTiddler" value=<<target>> >
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The settings for <<currentTiddler>> are: <<settings>>
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</$set>
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</$set>
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</$set>
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</$set>
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```
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! Remarks
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This widget differs from <<.wid vars>> in the following way:
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* Each variable's definition will be immediately available to all proceeding variables in the same let widget. This differs from vars, in which definitions which depend on some variable will always look to the widget's outer scope for a value.
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This widget differs from <<.wid set>> in the following ways:
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* A fallback (also known as "emptyValue") cannot be specified
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* Filters cannot be used to produce a conditional variable assignment
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* Variable names must be literal strings
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