title: How to find if a function exists in PostgreSQL?
body: <p>Unlike tables or sequences, user-defined functions cannot be found through <a href="http://www.postgresql.org/docs/9.3/static/catalog-pg-class.html" rel="noreferrer">pg_class</a>. There are questions on <a href="https://stackoverflow.com/q/1347282/1801588">how find a list of all functions to delete</a> or <a href="https://stackoverflow.com/q/24033587/1801588">grant</a> them, but how to find an individual function (with known name and argument types) is not self-evident from them. So how to find whether a function exists or not?</p>
  
  <p>EDIT: I want to use it in a function, in automated manner. Which solution is the best performance-wise? Trapping errors is quite expensive, so I guess the best solution for me would be something without the extra step of translating error to false, but I might be wrong in this assumption.</p>