Notes:
Outlined above is the M language divided into four general categories of commands: I/O, Flow Control, Data manipulation and System.
These commands are structured around the concept of an expression which is central to the language. The expression can be viewed as layers, starting at the bottom: ASCII character set, String type specification, Symbol specification, Functions, Indirection and Operators.
These components of the language live in the System Space.
Within the Process Space exists the routine body that contains the code (procedurally ordered command and expressions). Flow control commands are instrumental in creating the code body for a specific application.
Embedded in the M specification are Data Manipulation commands that let the programmer manipulate data between the persistent database and a local symbol table that resides in the Process Space.
Additionally, embedded in the language are 5 I/O commands that were designed to control system devices such as dumb terminals, magtapes, sequential disk devices, etc.