Editing Standard ML (section)

====Exhaustiveness checking====
Pattern-exhaustiveness checking will make sure that each constructor of the datatype is matched by at least one pattern. 

The following pattern is not exhaustive:

<syntaxhighlight lang="sml">
fun center (Circle (c, _)) = c
  | center (Square ((x, y), s)) = (x + s / 2.0, y + s / 2.0)
</syntaxhighlight>

There is no pattern for the {{code|Triangle}} case in the {{code|center}} function. The compiler will issue a warning that the case expression is not exhaustive, and if a {{code|Triangle}} is passed to this function at runtime, {{code|lang=sml|exception Match}} will be raised.