112 lines
4.3 KiB
Markdown
112 lines
4.3 KiB
Markdown
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SilverBullet has a simple expression language that is used by the [[Query Language]], [[Template Language]] and `where` condition in [[Live Template Widgets]].
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Examples in this page will be demonstrated by embedding expressions inside of a [[Templates|template]].
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While a custom language, it takes a lot of inspiration from JavaScript and SQL, but includes some features very specific to SilverBullet, including syntax for embedded queries and page references.
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# Primitive values
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* strings: `"a string"`, `'a string'` or `a string` (with backticks). Escaping is not currently supported, so use your quotes wisely.
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* numbers: `10`
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* booleans: `true` or `false`
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* regular expressions: `/[a-z]+/`
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* null: `null`
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* lists: `["value 1", 10, false]`
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* objects: `{"name": "Jack", "age": 1232}`
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* attributes:
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* `.` for the current object
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* `attr` for the current object’s attribute with the name `attr`
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* `<expression>.attr` to access an attribute from the object that `<expression>` evaluates to
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* variables: `@page`
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## Examples
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```template
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String expression: {{"This is a string"}}
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List expression: {{[1, 2, 3]}}
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Attribute of variable: {{@page.name}}
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```
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# Function calls
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* `functionName(argument1, argument2, ...)`: call function `functionName`
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* `functionName`: call `functionName` without any arguments
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## Examples
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```template
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Today with argument list: {{today()}}
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Today without an argument list: {{today}}
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```
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## Supported functions
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[[Functions]]
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# Queries
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Expression can include [[Query Language|queries]] using the `{ page limit 1 }` syntax. Queries evaluate to one of two things:
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* Queries with a `render` or `render all` clause will evaluate a string, where the referenced template is applied (similar to [[Live Queries]]).
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* Queries _without_ a `clause` will evaluate to a list of results.
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Note that you can reference variables inside your query as well.
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## Example
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Incomplete task:
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* [ ] This task is not yet complete
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```template
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Number of incomplete tasks on this page: {{count({task where not done and page = @page.name})}}
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A rendered query:
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{{{page limit 3 render [[Library/Core/Query/Page]]}}}
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```
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# Page references
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Page references use the `[[page name]]` syntax and evaluate to the content of the referenced page (as a string), this makes them a good candidate to be used in conjunction with [[Functions#template(text, value)]] or to simply inline another page:
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```template
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Including another page directly, without template rendering: {{[[internal/test page]]}}
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And rendered as a template: {{template([[internal/test page]], "actual value")}}
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```
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# Logical expressions
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* and: `name = "this" and age > 10`
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* or: `name = "this" or age > 10`
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## Examples
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```template
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Simple boolean expression: {{"pete" = "pete" or "hank" = "pete"}}
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```
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# Operators
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* `=` equals
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* For scalar values this performs an equivalence test (e.g. `10 = 10`)
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* If the left operand is an array and the right operand is _not_, this will check if the right operand is _included_ in the left operand’s value, e.g. `[1, 2, 3] = 2` will be true.
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* If both operands are arrays, they will be compared for equivalence ignoring order, so this will be true: `[1, 2, 3] = [3, 2, 1]`
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* `!=` the exact inverse of the meaning of `=`, e.g. `name != "Pete"`
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* `<` less than, e.g. `age < 10`
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* `<=` less than or equals, e.g. `age <= 10`
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* `>` greater than, e.g. `age > 10`
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* `>=` greater than or equals, e.g. `age >= 10`
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* `=~` to match against a regular expression, e.g. `name =~ /^template\//`
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* `!=~` to not match a regular expression, e.g. `name !=~ /^template\//`
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* `in` member of a list (e.g. `prop in ["foo", "bar"]`)
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* `+` addition (can also concatenate strings), e.g. `10 + 12` or `name + "!!!"`
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* `-` subtraction, e.g. `10 - 12`
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* `/` addition, e.g. `10 / 12`
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* `*` multiplication, e.g. `10 * 12`
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* `%` modulo, e.g. `10 % 12`
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* `not <expression>` or `!<expression>` to negate the truthiness value
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* `<expression> ? <ifTrue> : <ifFalse>`
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## Operator precedence
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Operator precedence follows standard rules, use parentheses when in doubt, e.g. `(age > 10) or (name = "Pete")`
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## Examples
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```template
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Some arithmatic: {{10 * 100 / 1000}}
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Some regexp match: {{"hello" =~ /ell/}}
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Some list check: {{["template", "other"] = "template"}}
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{{8 > 3 ? "8 is larger than 3" : "8 is not larger than 3"}}
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```
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# Comments
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Line comments are supported via `# this is a line comment`
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