Expression language definition

The internal expression engine is Expr. You can find exhaustive documentation on the possibilities of the language at this address.

Supported Literals

• strings - single and double quotes (e.g. "hello", 'hello')
• numbers - e.g. 103, 2.5
• arrays - e.g. [1, 2, 3]
• maps - e.g. {foo: "bar"}
• booleans - true and false
• nil - nil

Accessing article properties

Article properties can be accessed by using their name:

• Title: Article title
• Text: Article text description
• Content: Article HTML content
• Link: Article URL
• Meta["key"]: Metadata value
• Tags: Array of tags

Supported Operators

Comparison Operators

• == (equal)
• != (not equal)
• < (less than)
• > (greater than)
• <= (less than or equal to)
• >= (greater than or equal to)

Logical Operators

• not or !
• and or &&
• or or ||

String Operators

• + (concatenation)
• matches (regex match)
• contains (string contains)
• startsWith (has prefix)
• endsWith (has suffix)
• toLower (to lower case)
• toUpper (to upper case)

To test if a string does not match a regex, use the logical not operator in combination with the matches operator:

not (Title matches "^b.+")

You must use parenthesis because the unary operator not has precedence over the binary operator matches.

Example:

'Arthur' + ' ' + 'Dent'

Result will be set to Arthur Dent.

Membership Operators

• in (contain)
• not in (does not contain)

Example:

"test" in Tags

meta.author in ['me', 'other']

Builtin functions

• len (length of array or string)
• all (will return true if all element satisfies the predicate)
• none (will return true if all element does NOT satisfies the predicate)
• any (will return true if any element satisfies the predicate)
• one (will return true if exactly ONE element satisfies the predicate)
• filter (filter array by the predicate)
• map (map all items with the closure)

Example:

len(Text) > 200

Closures

• {...} (closure)

Closures allowed only with builtin functions. To access current item use # symbol.

one(tags, {# == 'test'})