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1
2 As documentation for the program life.i, I am including below the original
3 posting message, with the program itself deleted. The present program
4 life.i is nearly identical to the one that was posted. The only two
5 changes are that I have fixed a bug where a 32-bit number was assigned
6 to a 16-bit variable, and I have streamlined the decrement routine---
7 entry points (2000) and (2010)---by eliminating a temporary variable.
8 The old versions of these code fragments are included at the end of
9 the file.
10
11 Louis Howell
12 November 24, 1991
13
14 -----------------------------------------------------------------------------
15
16 Subject: Life with Intercal (long)
17 Newsgroups: alt.lang.intercal
18 From: Louis Howell
19 Date: Mon, 28 Jan 91 09:17:36 PST
20
21 I suppose some of you are wondering if anyone ever actually writes anything
22 in Intercal, or if we all just sit around beating on the compiler and
23 talking about how wonderful this crock would be if XXX feature were added
24 to it. I submit the following beast as a demonstration that a vaguely
25 interesting program can be written in the language. Of course, none of
26 you can actually RUN this program, since the 0.6 compiler doesn't handle
27 arrays. Take my word for it that it works, and I promise to finish up
28 a couple of remaining details in the array implementation and send it
29 off to Steve Real Soon Now (sometime this week, with luck).
30
31 The program first takes three numbers as input: The dimensions of the
32 grid and the desired number of time steps. It then accepts pairs of
33 numbers indicating which cells are live in the initial state; this
34 list of pairs is terminated by a ZERO or OH. Then it plays Life.
35 When the final timestep is reached, or when the system overflows the
36 grid, the program prints out pairs of numbers indicating which cells
37 were live in the last state reached, followed by the number of time
38 steps that were actually executed.
39
40 The implementation is not as efficient as it could be by a long shot---
41 I just wanted to get something that worked. I use two arrays, ,1 and ,2,
42 both with dimensions .11 BY .12. At each time step the next position
43 based on data in ,1 is computed and stored in ,2 for all cells in the
44 interior of the grid. Then this portion of the grid is copied back
45 into ,1. (The cells on the edge of the grid are never changed, they just
46 hold zeroes that are seen by the neighborhood calculations of interior
47 cells.) Then the current time step is incremented, and if equal to the
48 desired final time step the program jumps to the output routine. If
49 not, it checks the ring of cells next in from the edge cells. If it
50 finds three live cells in a row on one of the interior edges it jumps
51 to the output routine, since on the next timestep the configuration
52 would overflow into the boundary ring. Note that this boundary check
53 is not done until after the first time step, so the user is responsible
54 for providing an input state that is not about to overflow.
55
56 An overflow recovery procedure that actually increased the size of the
57 grid might be interesting, but wouldn't be terribly practical since
58 any configuration that throws off gliders would quickly push it to the
59 limit.
60
61 The following configuration has four live cells and grows into traffic
62 lights. To see the blinkers in the other position, change the final
63 time step from ONE OH to NINE or ONE ONE.
64
65 ONE ONE
66 ONE ONE
67 ONE OH
68 FIVE
69 SIX
70 SIX
71 SIX
72 SEVEN
73 SIX
74 SIX
75 SEVEN
76 OH
77
78 This is a glider aimed up the main diagonal. Specifying ZERO for the
79 final timestep tells the program to run until overflow, since the first
80 test is at step one. In this case it halts at step XVI with the glider
81 translated four cells up the diagonal. You can make it run longer by
82 increasing the dimensions of the array.
83
84 NINE
85 NINE
86 ZERO
87 TWO
88 FOUR
89 THREE
90 FOUR
91 FOUR
92 FOUR
93 FOUR
94 THREE
95 THREE
96 TWO
97 OH
98
99 Here are a few of the features of the program which may be of interest to
100 Intercal programmers. One obvious one not mentioned in the manual is the
101 test for equality: XOR the two numbers and test if the result is zero.
102 There are many examples of indexed loops. The loops over array indices
103 fall into two different classes, decrement and branch on zero, and
104 decrement and branch on equal. The time step loop uses increment and
105 branch on equal. The nested loop computing the next state has three
106 indices for each dimension, since it is easier to keep i-1, i and i+1
107 around than to recompute them on the fly. This also allows me to use
108 the simpler branch on zero test at the base of these loops since i-1 was
109 already available.
110
111 Three new subroutines may be of general interest. Line (2000) is the
112 entry point for a decrement routine setting .1 <- .1 minus #1. This
113 is very similar to the increment routine (1020) in the system library,
114 which I also use. Line (2010) is the decrement and branch on zero
115 operation. It decrements .1, then if .1 is not zero returns to the
116 calling point, but if .1 is zero pops an additional entry off the
117 RESUME stack and returns to that point instead. Line (2020) is an
118 alternative entry point to the (1020) routine which performs an add
119 bit operation. It sets .1 <- .1 plus .2, where .2 is already known
120 to be either #0 or #1.
121
122 The need for some kind of string I/O is painfully obvious. It would be
123 so much nicer to be able to show the final state using a grid of O's and
124 .'s instead of having to print out all the coordinates. I have some more
125 ideas about string I/O which I will post later.
126
127 Enough talk, on with the program:
128
129
130 [Program deleted, see life.i for the current version.]
131
132
133 This is where the original program had an assignment type error:
134
135 DO .2 <- #0$#65535
136 DO .1 <- "?'"V.1$,1SUB.7.8"~.2'$#3"~.2
137 DO ,2 SUB .7.8 <- "?!1~.1'$#1"~#1
138
139 This is the old, less efficient version of the decrement routine:
140
141 (2010) PLEASE ABSTAIN FROM (2004)
142 (2000) PLEASE STASH .2 + .3
143 DO .2 <- #1
144 DO (2001) NEXT
145 (2001) PLEASE FORGET #1
146 DO .1 <- '?.1$.2'~'#0$#65535'
147 DO .3 <- "?!1~.2'$#1"~#3
148 DO (2002) NEXT
149 DO .2 <- !2$#0'~'#32767$#1'
150 DO (2001) NEXT
151 (2003) PLEASE RESUME .3
152 (2002) DO (2003) NEXT
153 PLEASE RETRIEVE .2 + .3
154 (2004) PLEASE RESUME #2
155 PLEASE DO REINSTATE (2004)
156 PLEASE RESUME '?"!1~.1'~#1"$#2'~#6
157
158 --
159 Louis Howell
160
161 "But when we got into the street I viddied that thinking is for the gloopy
162 ones and that the oomny ones use like inspiration and what Bog sends."