Loop Invariants

Here is an example of moving part of a tuple's initialization out of a loop:

type tupleType = int32 invary, int32 vary;
type listOfTuples = list<tupleType>;

void createListOfTuples (mutable listOfTuples a,int32 start, int32 n) {
  mutable int32 i = 0;
  while (i < n) {
    appendM(a, {invary = n, vary = start + i} );
    ++i;
  }
}

In the example, a new tuple is created and initialized for each iteration of the loop. Notice that only the vary attribute changes in the loop. So instead of creating the tuple in the loop, you can create it outside of the loop. Then, for each iteration of the loop you can set the vary attribute as follows:

void createListOfTuples (mutable listOfTuples a,int32 start, int32 n) {
  mutable int32 i = 0;
  mutable tupleType t = {invary = n, vary = 0};
  while (i < n) {
    t.vary = start + i;
    appendM(a,t);
    ++i;
  }
}

This technique saves the creation and part of the initialization of the tuple for each loop iteration. Similar techniques can be used when you submit tuples from an operator.