[[Recursive patterns]] is a [[Stratego idiom]] for checking the format of terms by means of recursion and congruences. This idiom is useful for checking the conformance of terms to some signature. Moreover it can be used to check conformance to some subset of terms generated by a signature. For example, checking that some [[abstract syntax tree]] corresponds to the desugared subset of the [[abstract syntax]].

[[Recursive patterns]] where first described in the [[Strategic pattern matching]] paper.

A recursive pattern has the following format

<verbatim>
strategies
  LambdaExp =
	 rec x(
		Var(is-string)
		+ Lambda(Var(is-string), x)
		+ App(x, x)
	 )
</verbatim>

This recursive pattern assumes a signature that defines the constructors Var/1, Lambda/2 and App/2. For example as follows:

<verbatim>
signature
  sorts Lexp
  constructors
	 Var	 : String -> Var
	 Lambda : Var * Lexp -> Lexp
	 App	 : Lexp * Lexp -> Lexp
			  : Var > Lexp
</verbatim>