COMMENT ⊗   VALID 00008 PAGES
C REC  PAGE   DESCRIPTION
C00001 00001
C00002 00002	system features
C00003 00003	show sos line editing
C00004 00004	flashes
C00005 00005	wise: a desk calculator (circa 1966, pdp-1) 
C00006 00006	FACTORIAL DEBUGGING IN MACHINE LANGUAGE  (RAID: circa 1964, pdp-1)
C00008 00007	IN LISP  (1958, ibm704)
C00011 00008	TIME PERMITTING (REWRITE)
C00012 ENDMK
C⊗;
system features
displays
multiplexing dpys and keyboard mapping
line editing

show sos line editing


the display editor. (derivative of TVEDIT, circa 1965, pdp-1)


show teach file

features:
attach and copy modes
pages and directory
marks
searches

CREATE UPSET
flashes

DIRED
COOPERATION OF DISPLAY WITH INCOMING MESSAGES.
HOT
music
xgp
ddfont
xgpsyn
spell (using display, word selection by numbers), accept, and replace

wise: a desk calculator (circa 1966, pdp-1) 
24
βR
=
*

*****DON'T FORGET "Q"***** IN FACT(24)

*** DO "IMPLIED" *


Lα LOADS MACRO
Sα SAVES IT
Kα COMPILES
Pα PRINTS CODE

MF
(A)IF A=0 THEN RETURN (1) ELSE RETURN A*F(A-1)
<alt>
E
3
<cntrl>F
MF
Z1
add BEGIN PAUSE HIYA; ....  END
E
3
<cntrl>F

PF
FACTORIAL DEBUGGING IN MACHINE LANGUAGE  (RAID: circa 1964, pdp-1)

assemble fact: debug fact

clear screen: βi

load up screen: FACT; >>>>>>>>>>

note that FACT is preempted by DDTEND; kill it: DDTENDαk 

open and protect AC1, AC2, P: <name>; α;  or <name>α;

dynamically open P:  Pε[ 

now notice  that we neglected to initialize the stack
designated by P.

 1. define PATCH as START+5:  PATCH ← START+5
 2. stuff P with stack pointer: P;-300,,PATCH
      note dynamic update of P and tos.

ready to execute; go to start for single step: START;

single step: βs

note that MOVEI AC1,0 is wrong, and fix: 
 1. arrow to START: β<
 2. get MOVEI AC1,0 in line buffer to edit: βE
 3. edit (search 0, type 1) and replace (<cr>)

single step through fact(1) and fact(2)

notice that fact(3) is wrong; and source of bug is
premature subtract. fix it by retying instrs. in opposite order
 
move to start and βs through fact(3); it works

since we believe fact works we βx-it.
the result is 30; convert to decimal: AC1; αd

do fact(6)

IN LISP  (1958, ibm704)

write improper definition:

(DE FACT (X)(COND((ZEROP X) L)(T(TIMES X (SUB1 X <alt>

this is supposedly a representation of:

fact[x] <= [x=0 → 1; t → *[x;fact[x-1]]]

do (FACT 0)

it breaks at L; type >1 to replace L by 1 and continue.

do (FACT 4)
 it gives 14 (octal) change base and get 12.
  notice loss in  definition and call editor

(EDITF FACT $

nP down to  (& & (SUB1 X))
(BI 2)    insert parens (incorrectly) on second element
(UNDO)    correct correction
(BI 3)    do it right
3P        move to third element and print it
(-1 FACT) add FACT as first element of list.
↑	  go up to top-level structure
PP	  and print it.
OK	  bless it and leave

(TRACE FACT)


**********
DEFINE 
f[x] <= [x=0 → 1; t → g[x]]
(DE F (X)(COND ((ZEROP Z) 1)(T (G X)))

do (F 1)

do (F 2)
  G  breaks
    at least three options:
	1. >FACT     replace G by FACT

	2. (DE G (X)(TIMES X(F (SUB1 X))))  define G
	   GO         ... and continue

	3. BKV      patch F
	   EDIT -1  edit part of the saved stack
	   F G        by locating G,
	   UP         getting "above" (G X)
	   P	      check it
	   (1 (TIMES X (F (SUB1 X)))) replace first element with (TIMES ...)
	   ↑         check it
	   PP
	   OK	     exit editor to break package
	   FROM?=    exit break with stack pushed back to  edited expression.

TIME PERMITTING (REWRITE)

reduce: a macsyma-like LISP-based language

2+3;
5
2+4+(x+y+x);
2x+y+6



other pdp-1  programs: Culler-Fried