Syntax Reference

The Comby syntax below has special meaning for matching. Bind match contents to identifiers like hole using Named Match syntax. Using names is useful when replacing contents or writing rules. To just match patterns without giving a meaningful name, use any of the Just Match syntax.

Match and Rewrite Syntax

Named Match	Just Match	Description
`:[var]`	`...` `:[_]`	match zero or more characters in a lazy fashion. When used is inside delimiters, as in `{:[v1], :[v2]}` or `(:[v])`, holes match within that group or code block, including newlines. Holes outside of delimiters stop matching at a newline, or the start of a code block, whichever comes first.
`:[var~regex]`	`:[~regex]`	match an arbitrary PCRE regular expression `regex`. Avoid regular expressions that match special syntax like `)` or `.*`, otherwise your pattern may fail to match balanced blocks.
`:[[var]]`	`:[~\w+]` `:[[_]]`	match one or more alphanumeric characters and `_`.
`:[var:e]`	`:[_:e]`	Expression-like syntax matches contiguous non-whitespace characters like foo or foo.bar, as well as contiguous character sequences that include valid code block structures like balanced parentheses in `function(foo, bar)` (notice how whitespace is allowed inside the parentheses). Language-dependent.
`:[var.]`	`:[_.]`	match one or more alphanumeric characters and punctuation like `.`, `;`, and `-` that do not affect balanced syntax. Language dependent.
`:[var\n]`	`:[~.*\n]` `:[_\n]`	match zero or more characters up to a newline, including the newline.
`:[ var]`	`:[var~[ \t]+]` `:[ ]`	match only whitespace characters, excluding newlines.

Rewrite Properties

String converters

Property	Behavior
`.lowercase`	Convert letters to lowercase
`.UPPERCASE`	Convert letters to uppercase
`.Capitalize`	Capitalize the first character if it is a letter
`.uncapitalize`	Lowercase the first character if it is a letter
`.UPPER_SNAKE_CASE`	Convert `camelCase` to `snake_case` (each capital letter in `camelCase` gets a `_` prepended). Then uppercase letters.
`.lower_snake_case`	Convert `camelCase` to `snake_case` (each capital letter in `camelCase` gets a `_` prepended). Then lowercase letters.
`.UpperCamelCase`	Convert `snake_case` to `CamelCase` (each letter after `_` in `snake_case` is capitalized, and the `_` removed). Then capitalize the first character.
`.lowerCamelCase`	Convert `snake_case` to `CamelCase` (each letter after `_` in `snake_case` is capitalized, and the `_` removed). Then lowercase the first character.

Sizes

Property	Behavior
`.length`	Substitute the number of characters of the hole value
`.lines`	Substitute the number of lines of the hole value

Positions

Property	Behavior
`.line`	Substitute the starting line number of this hole
`.line.start`	Alias of `.line`
`.line.end`	Substitute the ending line number of this hole
`.column`	Substitute the starting column number of this hole (also known as `character`)
`.column.start`	Alias of `.column`
`.column.end`	Substitute the ending column number of this hole
`.offset`	Substitute the starting byte offset of this hole in the file
`.offset.start`	Alias of `.offset`
`.offset.end`	Substitute the ending byte offset of this hole in the file

File context

Property	Behavior
`.file`	Substitute the absolute file path of the file where this hole matched
`.file.path`	Alias of `.file`
`.file.name`	Substitute the file name of the file where this hole matched (`basename`)
`.file.directory`	Substitute the file directory of the file where hole matched (`dirname`)

Identity

Property	Behavior
`.value`	Substitute the text value of this hole