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APLSF (System Function) is an implementation of the APL programming language for TOPS-20 that is available on TWENEX.

In and Out

To start the APL interpreter, type the following from EXEC:


At the terminal.. prompt, enter tty for a non-APL keyboard.

Leave APLSF by entering one of the following commands (APLSF converts all alphabetic input to upper-case):

)MONTerminate APLSF and return to EXEC.
)OFFTerminate APLSF and log out of TWENEX.
)CONTINUESave active workspace to file DSK:CONTIN.APL, terminate APLSF, log-out from TWENEX. The saved workspace will be loaded automatically the next time you run APLSF.

To interrupt APLSF during execution, press Ctrl-C once or twice.

Press Ctrl-C five (5) times to suspend APLSF and return to EXEC. Resume APLSF with command @REENTER or @CONTINUE.

APL Character Set

Although APL characters cannot be displayed or input when the terminal is in TTY mode, APLSF provides ASCII character string equivalents for all the APL characters as well as “escape mode” (single character preceded by “@”) keys that correspond to standard APL keyboard mappings. ASCII and escape mode sequences can be intermixed.

Name ASCII Escape
and & Grade Down .GD
assignment _ Grade Up .GU
÷ divide % I-Beam (histogram) .IB
exponentiate * @E LoGarithm .LG
× multiply # NaNd .NN
? question (roll and deal) ? @Q NoR .NR
' quote string ' @K back expansion .CB
take ^ @Y (Circle) Rotate .CR
residue (ABsolute value) .AB @M back scan .CS
α ALpha .AL @A Divide Quad .DQ
quad (BoX) .BX @L Input Quad .IQ
CEiling (maximum) .CE @S Output Quad .OQ
drop (Down Arrow) .DA @U OUt .OU
¨ Dieresis .DD Protected Del .PD
DEcode .DE @B Quad Del .QD
DeL .DL @G Quad Quote .QQ
DiaMond .DM ReVersal .RV
Down Under .DU @C TRanspose .TR
ENcode .EN @N eXecute .XQ
EPsilon .EP @E ForMat .FM
FLoor .FL @D Comment (lamp)
Greater then or Equal to .GE A-Z underscored alphabetics .ZA-.ZZ
GO to (branch) .GO underscored lower del .Z@
IOta .IO @I
{ Left curly Brace .LB
delta (Lower Del) .LD @H
Less than or Equal to .LE
Left tacK .LK
circle (Large O) .LO @O
Left Union .LU @X
Not Equal to .NE
NeGation .NG
NoT .NT @T
OMega .OM @W
} Right curly Brace .RB
RhO .RO @R
Right tacK .RK
Right Union .RU @Z
jot (Small O) .SO @J
_ UnderScore .US @F
Up Union .UU @V

Workspace Commands

)SAVE [wsname]Save workspace in file DSK:wsname.APL.
)LOAD wsnameLoad saved workspace from file DSK:wsname.APL.
)DROP wsnameDelete saved workspace file DSK:wsname.APL.
)CLEARClear active workspace.
)FNS [letter]List functions in workspace (starting alphabetic list from letter).
)VARS [letter]List global variables in workspace (starting alphabetic list from letter).
)ERASE nameErase global variable or function name from workspace.

Function Editor

To define a new function and invoke the editor, enter one of the following commands:

.DL[r_]a1 f a2[;v]…Define a dyadic (two-argument infix) function
.DL[r_]f a1[;v]…Define a monadic (one-argument prefix) function
.DL[r_]f[;v]…Define a niladic (no-argument) function


fFunction name
a1, a2Dummy arguments
rDummy variable for return value
vLocal variable

To edit an existing function, enter the command .DLf.

The editor will start and prompt with the current line number, for example [1].

Editor commands

textAdd text at current line.
[n]textReplace line n with text. Edit the function header as line 0.
[n.m]textInsert text as new line after line n. (Lines are automatically renumbered after each editing session.)
[.LDn]Delete line n.
[.BX]List function source.
[n.BX]List line n.
[.BXn]List from line n to the end of the function.
.DLSave function and return from editor.

Multiple commands can be entered on a single line. For an example, you can open the editor on existing function FUN1, list its source, and immediately exit the editor by entering the following command in the APL interpreter:



apl.txt · Last modified: 2021/12/04 07:35 by papa