Direct Mode is an important tool in GT.M because it allows you to interactively debug, modify, and execute M routines. Direct Mode is a shell that immediately compiles and executes GT.M commands providing an interpretive-like interface. M simplifies debugging by using the same commands for debugging that are used for programming.

The focus of this chapter is to describe the debugging process in Direct Mode, and to illustrate the GT.M language extensions that enhance the process. Command functionality is described only in enough detail to illustrate why a particular command is useful for a debugging activity being described. If you have specific functionality questions about a command or variable, see the “Commands”, “Functions”, or “Intrinsic Special Variables” chapter.

It is also from Direct Mode that you activate GT.M tools used to create M source code. The interaction of M commands used for editing and compiling is described in greater detail within Chapter 3: “Development Cycle”.