Op      Code written
--------------------------------------------
:x      None (defines label x)

cx      Call to label x
jx      Jump to label x
fx      Jump to label x if zero
tx      Jump to label x if non-zero
r       Return

        Set A to ...
'x      ... symbol/character x
dn      ... 10*A + n, where n is a decimal digit (0-9)
0       ... nil (same as number 0)
"xyz"   String is copied to output literally (typically surrounded by
        a jump, label, and code to do something with the string)
@x      Absolute address of label x

l       Lookup low byte of A in current env
bx      Extend current env with x bound to value in A
e       Set current environment to the one in E ("enter E")
s       Set E to current environment
{       Push current environment onto stack
}       Pop environment from stack and make it the current one

[       Push <A,E> onto stack
]       Pop <A,E> from stack

a       Apply function popped from stack to argument <A,E>, leaving
        the current (or previous after apply) environment on the stack