A method for hosting a programming environment and processing user input includes the step of receiving, during a first session between a user and an interaction environment, via one of a plurality of media gateways, a definition of an expression type, the definition specifying an expression format and a response type. The definition is stored. During a second session between a second user and the interaction environment, an expression having a semantic structure is received, from a user, via one of a plurality of media gateways. The semantic structure of the expression is evaluated. An expression format of the received expression is identified as the expression format specified by the definition of the expression type, responsive to the evaluation. A response to the expression is generated responsive to an execution of a computer program associated with the response type specified by the definition of the expression type.