In this paper we introduce the notion of implementations of parameterized data types generalizing our algebraic implementation concept of actual types as studied in earlier papers.
A typical example is the implementation of binary trees bintree(data), by strings with brackets bracketstring(data), where data is the common formal parameter part of both parameterized specificitions. Parameter passing means to replace the formal parameter data by an actual parameter like integers int leading to bintree(int) and bracketstring(int) respectively. The main result of this paper shows that parameter passing commutes with implementation. This means for our example that starting with a correct implementation of bintree(data) by bracketstring(data) correct parameter passing from data to int leads to a correct induced implementation of bintree (int) by bracketstring(int) where the induced implementation is an algebraic implementation of actual types as studied in our earlier papers. In other words the following diagram of parameter passing and implementations commutes: .