:PROPERTIES: :ID: c8eaf537-45ed-4043-89cf-6bed37b2a811 :mtime: 20231018022918 :ctime: 20231018022833 :END: #+title: Exceptions (programming) #+filetags: :public:project: * Definition In programming languages, an exception is a feature which, when an exception is encountered, program execution immediately stops. Some programming languages allow programs to handle exceptions, meaning that execution will resume. * Examples of Exceptions Let us look at how different programming languages implement exceptions ** Exceptions in [[id:8952459c-5076-4e68-8a68-5f658209f39e][Ocaml]]. *** Defining a new exception in ocaml #+BEGIN_SRC ocaml exception Change of int #+END_SRC #+RESULTS: : exception Change of int *** Raising and handling exceptions in ocaml #+BEGIN_SRC ocaml :exports both try print_endline "before the exception" ; raise (Change 5) ; print_endline "after the exception"; with | Change x -> print_endline "handled the exception" #+END_SRC #+RESULTS: : () *** Using exceptions to alter control flow This example comes from [[id:d69438b9-c2e4-415a-9dbe-faf0fc810413][Coin Changing Problem]]. #+BEGIN_SRC ocaml exception NoChange let rec change till amount = match till , amount with | _ , 0 -> [] | [] , _ -> raise NoChange | coin :: till , amount -> if amount < 0 then raise NoChange else try coin :: change (coin :: till) (amount - coin) with NoChange -> change till amount #+END_SRC #+RESULTS: : <fun> #+BEGIN_SRC ocaml change [ 20 ; 10 ; 5 ; 2 ; 1] 17 #+END_SRC #+RESULTS: | 10 | 5 | 2 | #+BEGIN_SRC ocaml change [5 ; 2] 6 #+END_SRC #+RESULTS: | 2 | 2 | 2 |