Programming abstractions with at least one expression are composed to a single abstraction using a composition operator. Expressions from the abstractions are unfolded by removing the prefix of each abstraction and substituting formal parameter names in each expression with a common parameter name to define open variables. The unfolded expressions are transformed to a reduced expression using a composition pattern that tunes semantics of the composition operators. The reduced expression is nested in the single abstraction by: appending a selected prefix of the composed abstraction to the reduced expression, binding the open variables of the reduced expression to the formal parameter of the selected prefix, and computing the type of the formal parameter of the selected prefix.