Architecture Software Using: A Methodology for Language Development

I m p l e m e n t a t i o n . The abstract machine is then given an implementation (typ- ically, a library), or possibly many, to account for different operational con- texts. The valuation function can be implemented as an interpreter based on an abstract machine implementation, or as a compiler to abstract machine instructions. P a r t i a l e v a l u a t i o n . While interpreting is more flexible, compiling is more effi- cient. To get the best of both worlds, we use a program transformation tech- nique, namely, partial evaluation, to automatically transform a DSL program into a compiled program, given only an interpreter. Each of the above methodology steps is further detailed in a separate section of this paper. 1.6 A W o r k i n g E x a m p l e To illustrate our approach, an example of DSL is used throughout the paper. We introduce a simple electronic mail processing application as a working example. Conceptually this application enables users to specify automatic treatments of incoming messages depending on their nature and contents: dispatching mes- sages to people or folders, filtering spam, offering a shell escape (e.g., to feed an electronic agenda), replying to messages when absent, etc. This example is inspired by a Unix program called s l o c a l which offers users a way of processing inbound mail. With s l o c a l , user-defined treatments are expressed in the form of rules. Each rule consists of a string to be searched in a message field (e.g., Subjec t , From) and an action to be performed if the string