We introduce a DSL based toolchain supporting the design of parallel applications where parallelism is structured after parallel design pattern compositions. A DSL provides the possibility to write high level parallel design pattern expressions representing the structure of parallel applications, to refactor the pattern expressions, to evaluate their non-functional properties (e.g. ideal performance, total parallelism degree, etc.) and finally to generate parallel code ready to be compiled and run on different target architectures. We discuss a proof-of-concept prototype implementation of the proposed toolchain generating FastFlow code and show some preliminary results achieved using the prototype implementation.