catchcatch is a special form in `
C source code'. (catch TAG BODY...) Eval BODY allowing nonlocal exits using `throw'. TAG is evalled to get the tag to use; it must not be nil. Then the BODY is executed. Within BODY, a call to `throw' with the same TAG exits BODY and this `catch'. If no throw happens, `catch' returns the value of the last BODY form. If a throw happens, it specifies the value to return from `catch'.