theory TimeLimitimports "../Base"beginsection {* Restricting the Runtime of a Function *} text {* {\bf Problem:} Your tool should run only a specified amount of time.\smallskip {\bf Solution:} This can be achieved using the function @{ML timeLimit in TimeLimit}.\smallskip Assume the following well-known function: *}ML {* fun ackermann (0, n) = n + 1 | ackermann (m, 0) = ackermann (m - 1, 1) | ackermann (m, n) = ackermann (m - 1, ackermann (m, n - 1))*}text {* Now the call @{ML_response_fake [display] "ackermann (4, 12)" "\<dots>"} takes a bit long. To avoid this, the call can be encapsulated in a time limit of five seconds. For this you have to write:@{ML_response [display]"TimeLimit.timeLimit (Time.fromSeconds 5) ackermann (4, 12) handle TimeOut => ~1""~1"} where @{ML_text TimeOut} is the exception raised when the time limit is reached. Note that @{ML "timeLimit" in TimeLimit} is only meaningful when you use PolyML, because PolyML has a rich infrastructure for multithreading programming on which @{ML "timeLimit" in TimeLimit} relies.\begin{readmore} The function @{ML "timeLimit" in TimeLimit} is defined in the structure @{ML_struct TimeLimit} which can be found in the file @{ML_file "Pure/ML-Systems/multithreading_polyml.ML"}.\end{readmore}*}end