Additional Control Commands

Table 4-32 contains descriptions of additional program execution control commands.

Table 4-32 Program Execution Control Commands

Command	Stack Diagram	Description
abort	( -- )	Abort current execution and interpret keyboard commands.
abort" ccc"	( abort? -- )	If abort? is true, abort and display message.
eval	( addr len -- )	Interpret Forth source from addr len.
execute	( xt -- )	Execute the word whose execution token is on the stack.
exit	( -- )	Return from the current word. (Cannot be used in counted loops.)
quit	( -- )	Same as abort, but leave stack intact.

abort causes immediate termination and returns control to the keyboard. abort" is similar to abort but is different in two respects. abort" removes a flag from the stack and only aborts if the flag is true. Also, abort" prints any desired message when the abort takes place.

eval takes a string from the stack (specified as an address and a length). The characters in that string are then interpreted as if they were entered from the keyboard. If a Forth text file has been loaded into memory (see Chapter 5, Loading and Executing Programs), then eval can be used to compile the definitions contained in the file.