1. An electronic calculator comprising: keyboard input means having a plurality of alphabetic and numeric keys for entering alphameric information, including arithmetic expressions, into the calculator; memory means, coupled to said keyboard input means, for storing alphameric information entered into the calculator; processing means, coupled to said keyboard input means and memory means, for processing alphameric information entered into the calculator to perform selected functions; and output means, coupled to said processing means, for providing a visual indication of the results of selected functions performed by said processing means; said keyboard input means including an execute control key for initiating execution of an arithmetic expression entered into the calculator, a store control key for initiating storage of an arithmetic expression entered into the calculator, at least one definable key, and means for defining a function to be associated with each definable key, said store control key being operative for initiating storage of each such defined function in said memory means; said processing means being responsive to actuation of said execute control key, following actuation of a definable key and one or more other keys collectively representing an arithmetic expression for executing the defined function for that definable key as a part of that arithmetic expression, said processing means being further responsive to actuation of said store control key, following actuation of a definable key and one or more other keys collectively representing an arithmetic expression, for storing the defined function for that definable key as a part of that arithmetic expression in said memory means.