The Bulk Synchronous Parallel ML (BSML) library is a library for Bulk Synchronous Parallel (BSP) programming with the functional language Objective Caml. It is based on an extension of the lambda-calculus by parallel operations on a parallel data structure named parallel vector. This paper presents the execution model, given as a distributed semantics, of the parallel juxtaposition, a primitive of parallel composition for BSML. It also presents an implementation, which follows the semantics, and experiments using the parallel juxtaposition.