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[standard-ml/en-en] Exceptions

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David Pedersen 2013-12-05 12:33:02 +01:00
parent f1c96d5db0
commit a03869362b
1 changed files with 22 additions and 0 deletions
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standard-ml.html.markdown
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@ -302,6 +302,28 @@ fun count (Leaf n) = n
| count (Node (leftTree, n, rightTree)) = count leftTree + n + count rightTree
(* Exceptions! *)
(* Exceptions can be raised using "raise" *)
fun raiseException msg = raise Fail msg
(* This raises exception `Fail "hello from exception"` *)
(* val _ = raiseException "hello from exception" *)
(* Exceptions can be caught using "handle" *)
val x = raiseException "hello" handle Fail msg => msg
(* x now has the value "hello" *)
(* We can pattern match in "handle" to make sure
a specfic exception was raised, or grab the message *)
val y = raiseException "..." handle Fail _ => "Fail was raised"
| Domain => "Domain was raised"
(* y now has the value "Fail was raised" *)
(* We can define our own exceptions like this *)
exception MyException
exception MyExceptionWithMessage of string
(* File I/O! *)
(* Write a nice poem to a file *)
fun writePoem(filename) =