---
title: Pattern Synonym on multiple constructors
---

`ViewPatterns` can be used to define a pattern synonym matching on more than one constructor. An example:

```haskell
pattern Foo s <- 
  ((\case { SomeConstr1 _ s -> Just s; SomeConstr2 s -> Just s; _ -> Nothing }
   ) -> Just s
  )
```

lexi.lambda writes:

> The `Maybe` wrapping is there to communicate that the pattern-matcher should backtrack on anything other than `SomeConstr1` and `SomeConstr2`