1. A method using a computer for instrumenting in real time a computer program source code to facilitate the detection of runtime errors, the computer program being represented by a parse tree, each such runtime error having at least one instrumentation rountine for communicating an occurence of the associated runtime error to an error-checking engine, each such instrumentation routine being represented by a parse tree fragment, comprising the steps of: performing a real time flow analysis on the parse tree for the computer program to determine an appropriate instrumentation routine for detecting the runtime errors; instrumenting in real time the parse tree for the computer program by grafting the parse tree fragment for each such instrumentation routine onto the parse tree for the computer program; generating executable object code from the grafted parse tree containing references to the instrumentation routines; and executing the generated object code on a computer by transferring the runtime errors to the error-checking engine and linking the error-checking engine with the computer program to determine errors.