chickadee » srfi-146 » mapping-ref

mapping-ref mapping key failure successprocedure
mapping-ref mapping key failureprocedure
mapping-ref mapping keyprocedure

Extracts the value associated to key in the mapping mapping, invokes the procedure success in tail context on it, and returns its result; if success is not provided, then the value itself is returned. If key is not contained in mapping and failure is supplied, then failure is invoked in tail context on no arguments and its values are returned. Otherwise, it is an error.