2015-4: PDI - Progressive Dyadic Iota

The indexin function returns a simple integer vector that identifies where the major cells of Y are first found in X.

If a major cell of Y cannot be found in X, then the corresponding item of the returned array will be 1+≢X.

Progressive dyadic iota is similar to indexin except that it returns the index of subsequent matches in the first argument until they are exhausted.

Write code that implements progressive dyadic iota.