Commands used by the Y2.0 command interface:
 
 Commands to dispose of the current extension:
 :eval         Evaluate dialogues in the current extension
 :save         Save the current extension
 :kill         Forget about the current extension
 :list         Print the current extension
 
 Commands to load & run files (compilation units)
 :load file    Load a file into the system
 :compile file Compile a file to native code and save the binary
 :run file     Load a file and run `main'
 
 Commands to control the current module:
 :clear        Remove all saved definitions in the current module
 :module name  Set the current module
 :Main         Switch to an empty module named Main
 
 Other commands:
 :cd directory Set the current directory
 :p?           Describe available printers
 :p= p1 p2 ... Set the printers
 :p+ p1 p2 ... Enable selected printers
 :p- p1 p2 ... Disable selected printers
 :o?           Describe available optimizers
 :o= o1 o2 ... Set the optimizers
 :o+ o1 o2 ... Enable selected optimizers
 :o- o1 o2 ... Disable selected optimizers
 :(fn ...)     Evaluate a Lisp expression
 
 Abbreviations within the current extension:
 =exp          Creates a dialogue to print the expression under :e
 @exp          Creates a definition which will run the dialogue under :e