We report on the design and implementation of a programming tool, DynaMoW, to control interactive and incremental mathematical calculations to be presented on the web. This tool is implemented as a language extension of OCaml using Camlp4. Fragments of mathematical code written for a computer-algebra system as well as fragments of mathematical web documents are embedded directly and naturally inside OCaml code. A DynaMoW-based application is made of independent web services, whose parameter types are checked by the OCaml extension. The approach is illustrated by two implementations of online mathematical encyclopedias on top of DynaMoW.