An implementation-oriented semantics of Wadler's pretty-printing combinators

We present a new implementation of Wadler's pretty-printing combinators. In this implementation, the combinators explicitly manipulate document values, rather than being abstract syntax operators. The purpose of this paper is to advance a point of view about domain modelling and language embedding: that the first and most essential step in domain modelling is finding appropriate values to represent objects in the domain. In this case, we have found what appears to be the appropriate notion of "document value" (to the extent that Wadler's combinators represent an appropriate notion of "document"). We argue that proceeding from this point of view provides greater insight into the domain, as well as a more efficient implementation of the combinators. 1 Introduction In [1], John Hughes presented a case study in the embedding of a domain in a functional language. The domain was that of pretty-printing --- displaying a data type such as an abstract syntax tree neatly with appropriate indent..