Indentation Rules

There are a few types of indentation rules that can be applied to forms. These are configured by a map of rule targets to indenters. Each rule is specified with either a symbol or a regular expression pattern. Rules are matched against forms in the following order:

1. Check the qualified form symbol against the rule, including namespace.
2. Check the name of the form symbol against the rule symbol.
3. If the rule is a pattern, match it against the form symbol string.

This ordering allows you to provide specific rules for overlapping symbols from different namespaces, e.g. differentiating d/catch from catch.

Inner rules

An :inner rule will apply a constant indentation to all elements at a fixed depth. So an indent rule:

{foo [[:inner 0]]}

Will indent all elements inside a foo form by two spaces:

(foo bar
  baz
  bang)

While an indent rule like:

{foo [[:inner 1]]}

Will indent all subforms one level in:

(foo bar
  baz
  (bang
    quz
    qoz))

Sometimes it's useful to limit indentation to one argument of the surrounding form. For example, letfn uses inner indentation only in its binding vector:

(letfn [(double [x]
          (* x 2))]   ;; special indentation here
  (let [y (double 2)
        z (double 3)]
    (println y
             z)))     ;; but not here

To achieve this, an additional index argument may be used:

{letfn [[:inner 2 0]]}

This will limit the inner indent to depth 2 in argument 0.

Block rules

A :block rule is a little smarter. This will act like an inner indent only if there's a line break before a certain number of arguments, otherwise it acts like a normal list form.

For example, an indent rule:

{foo [[:block 0]]}

Indents like this, if there are more than 0 arguments on the same line as the symbol:

(foo bar
     baz
     bang)

But indents at a constant two spaces otherwise:

(foo
  bar
  baz
  bang)

Indents can be customized to use the nth argument as the basis for indenting.

For example,

{foo [[:block 1 2]]}

Will indent from

(foo bar baz
bang)

to

(foo bar baz
         bang)

Stair rules

A :stair rule is similar to :block, except that it tries to indent test/expression clauses as pairs. This can be used as an alternative styling for case, cond, cond->, etc.The expression forms will be given an extra level of indentation if they are on their own line:

{cond [[:stair 0]]}

(cond
  a? :a
  b? :b)

(cond
  a?
    :a
  b?
    :b)