The Intercal Programming Language
THE INTERCAL PROGRAMMING LANGUAGE
REFERENCE MANUAL
Donald R. Woods & James M. Lyon
Copyright Donald R. Woods & James M. Lyon 1973
INTERCAL
1. INTRODUCTION
The names you are about to ignore are true. However, the story has been changed
significantly. Any resemblance of the programming language portrayed here
to other programming languages, living or dead, is purely coincidental.
1.1 ORIGIN AND PURPOSE
The INTERCAL programming language was designed the morning of May 26, 1972
by Donald R. Woods and James M. Lyon, at Princeton University. Exactly when
in the morning will become apparent in the course of this manual. It was
inspired by one ambition; to have a compiler language which has nothing at
all in common with any other major language. By 'major' was meant anything
with which the authors were at all familiar, e.g., FORTRAN, BASIC, COBOL,
ALGOL, SNOBOL, SPITBOL, FOCAL, SOLVE, TEACH, APL, LISP, and PL/I. For the
most part, INTERCAL has remained true to this goal, sharing only the basic
elements such as variables, arrays, and the ability to do I/O, and eschewing
all conventional operations other than the assignment statement (FORTRAN
"=").
1.2 ACRONYM
The full name of the compiler is "Compiler Language With No Pronounceable
Acronym", which is, for obvious reasons, abbreviated "INTERCAL".
1.3 ACKNOWLEDGMENTS
The authors are deeply indebted to Eric M. Van and Daniel J. Warmenhoven,
without whose unwitting assistance this manual would still have been
possible.
2. FUNDAMENTAL CONCEPTS
In this section an attempt is made to describe how and why INTERCAL may be
used; i.e., what it is like and what it is good for.
2.1 SAMPLE PROGRAM
Shown below is a relatively simple INTERCAL program which will read in 32-bit
unsigned integers, treat them as signed, 2's-complement numbers, and print out
their absolute values. The program exits if the absolute value is zero. Note
in particular the inversion routine (statements 6 through 14), which could
be greatly simplified if the subroutine library (see section 5) were used.
A more detailed analysis of a program is made in section 6 of this manual.
DO (5) NEXT
(5) DO FORGET #1
PLEASE WRITE IN :1
DO .1 <- 'V":1~'#32768$#0'"$#1'~#3
DO (1) NEXT
DO :1 <- "'V":1~'#65535$#0'"$#65535'
~'#0$#65535'"$"'V":1~'#0$#65535'"
$#65535'~'#0$#65535'"
DO :2 <- #1
PLEASE DO (4) NEXT
(4) DO FORGET #1
DO .1 <- "'V":1~'#65535$#0'"$":2~'#65535
$#0'"'~'#0$#65535'"$"'V":1~'#0
$#65535'"$":2~'#65535$#0'"'~'#0$#65535'"
DO (1) NEXT
DO :2 <- ":2~'#0$#65535'"
$"'":2~'#65535$#0'"$#0'~'#32767$#1'"
DO (4) NEXT
(2) DO RESUME .1
(1) PLEASE DO (2) NEXT
PLEASE FORGET #1
DO READ OUT :1
PLEASE DO .1 <- 'V"':1~:1'~#1"$#1'~#3
DO (3) NEXT
PLEASE DO (5) NEXT
(3) DO (2) NEXT
PLEASE GIVE UP
2.2 USES FOR INTERCAL
INTERCAL's main advantage over other programming languages is its strict
simplicity. It has few capabilities, and thus there are few restrictions to
be kept in mind. Since it is an exceedingly easy language to learn, one
might expect it would be a good language for initiating novice programmers.
Perhaps surprising, than, is the fact that it would be more likely to
initiate a novice into a search for another line of work. As it turns out,
INTERCAL is more useful (which isn't saying much) as a challenge to
professional programmers. Those who doubt this need only refer back to the
sample program in section 2.1. This 22-statement program took somewhere
from 15 to 30 minutes to write, whereas the same objectives can be achieved
by single-statement programs in either SNOBOL;
PLEASE INPUT POS(0) ('-' ! '')
+ (SPAN('0123456789') $ OUTPUT)
+ *NE(OUTPUT) :S(PLEASE)F(END)
or APL;
[1] >-0=/?<-?
Admittedly, neither of these is likely to appear more intelligible to
anyone unfamiliar with the languages involved, but they took roughly 60
seconds and 15 seconds, respectively, to write. Such is the overwhelming
power of INTERCAL!
The other major importance of INTERCAL lies in its seemingly inexhaustible
capacity for amazing one's fellow programmers, confounding programming shop
managers, winning friends, and influencing people. It is a well-known and
oft-demonstrated fact that a person whose work is incomprehensible is held
in high esteem. For example, if one were to state that the simplest way to
store a value of 65536 in a 32-bit INTERCAL variable is:
DO :1 <- #0$#256
any sensible programmer would say that that was absurd. Since this is
indeed the simplest method, the programmer would be made to look foolish in
front of his boss, who would of course happened to turn up, as bosses are
wont to do. The effect would be no less devastating for the programmer
having been correct.
3. DESCRIPTION
The examples of INTERCAL programming which have appeared in the preceding
sections of this manual have probably seemed highly esoteric to the reader
unfamiliar with the language. With the aim of making them more so, we
present here a description of INTERCAL.
3.1 VARIABLES
INTERCAL allows only 2 different types of variables, the 16-bit integer
and the 32-bit integer. These are represented by a spot (.) or two-spot
(:), respectively, followed by any number between 1 and 65535, inclusive.
These variables may contain only non-negative numbers; thus they have the
respective ranges of values: 0 to 65535 and 0 to 4294967295. Note: .123 and
:123 are two distinct variables. On the other hand, .1 and .0001 are
identical. Furthermore, the latter may NOT be written as 1E-3.
3.2 CONSTANTS
Constants are 16-bit values only and may range from 0 to 65535. They are
prefixed by a mesh (#). Caution! Under no circumstances confuse the mesh
with the interleave operator, except under confusing circumstances!
3.3 ARRAYS
Arrays are represented by a tail (,) for 16-bit values, or a hybrid (;) for
32-bit values, followed by a number between 1 and 65535, inclusive. The
number is suffixed by the word SUB, followed by the subscripts, separated
optionally by spaces. Subscripts may be any expressions, including those
involving subscripted variables. This occasionally leads to ambiguous
constructions, which are resolved as discussed in section 3.4.3. Definition
of array dimensions will be discussed later in greater detail, since
discussing it in less detail would be difficult. As before, ,123 and ;123
are distinct. In summary, .123, :123, #123, ,123, and :123 are all
distinct.
3.4 OPERATORS
INTERCAL recognizes 5 operators--2 binary and 3 unary. Please be kind to
our operators: they may not be very intelligent, but they're all we've got.
In a sense, all 5 operators are binary, as they are all bit-oriented, but
it is not our purpose here to quibble about bits of trivia.
******* proofread versus the paper copy only this far !!!! ************
3.4.1 BINARY OPERATORS
The binary operators are INTERLEAVE (also called MINGLE) and SELECT, which
are represented by a change (c/) and a sqiggle [sic] (~), respectively.
The interleave operator takes two 16-bit values and produces a 32-bit result
by alternating the bits of the operands. Thus, #65535c/#0 has the 32-bit
binary form 101010....10 or 2863311530 decimal, while #0c/#65535 =
0101....01 binary = 1431655765 decimal, and #255c/#255 is equivalent to
#65535.
The select operator takes from the first operand whichever bits correspond
to 1's in the second operand, and packs these bits to the right in the result.
Both operands are automatically padded on the left with zeros to 32 bits
before the selection takes place, so the variable types are unrestricted.
If more than 16 bits are selected, the result is a 32-bit value, otherwise
it is a 16-bit value. For example, #179~#201 (binary value 10110011~11001001)
selects from the first argument the 8th, 7th, 4th, and 1st from last bits,
namely, 1001, which = 9. But #201~#179 selects from binary 11001001 the 8th,
6th, 5th, 2nd, and 1st from last bits, giving 10001 = 17. #179~#179 has the
value 31, while #201~#201 has the value 15.
Perhaps a simpler way of understanding the operation of the select operator
would be to examine the logic diagram on the following page (Figure 1), which
performs the select operation upon two 8-bit values, A and B. The gates used
are Warmenhovian logic gates, which means the outputs have four possible
values: low, high, undefined (value of an uninitialized flip-flop), and
oscillating (output of a NOR gate with one input low and the other input
connected to the output). These values are represented symbolically by '0',
'1', '?', and 'F'. Note in particular that, while NOT-0 is 1 and NOT-1
is 0 as in two-valued logic, NOT-? is ? and NOT-F is F. The functions
of the various gates are listed in Table 1.
3.4.2 UNARY OPERATORS
The unary operators are & (logical AND), V (logical OR), and V- (logical
XOR). This last character is obtained by overpunching a worm (-) on a V
(V). The operator is inserted between the spot, two-spot, mesh, or
what-have-you, and the integer, thus: .&123, #V123. Multiple unary
operators may not be concatenated, thus the form #V&123 is invalid. This
will be covered later when precedence is discussed. These operators perform
their respective logical operations on all pairs of adjacent bits, the
result from the first and last bits going into the first bit of the result.
The effect is that of rotating the operand one place to the right and
ANDing, ORing, or XORing with its initial value. Thus, #&77 (binary =
1001101) is binary 0000000000000100 = 4, #V77 is binary 1000000001101111 =
32879, and #?77 is binary 1000000001101011 = 32875.
3.4.3 PRECEDENCE
Precedence of operators is as follows:
[1]
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_________________
1) Keep in mind that the aim in designing INTERCAL was to have no
precedents.
This precedence (or lack thereof) may be overruled by grouping expressions
between pairs of sparks (') or rabbit-ears ("). Thus '#165c/#203'~#358
(binary value '10100101c11001011'~101100110) has the value 15, but
#165c/'#203~#358' has the value 34815, and #165c/#203~#358 is invalid
syntax and is completely valueless (except perhaps as an educational tool
to the programmer). A unary operator is applied to a sparked or rabbit-eared
expression by inserting the operator immediately following the opening spark
or ears. Thus, the invalid expression #V&123, which was described earlier,
could be coded as 'V#&123' or 'V"{"'. Note: In the interests of
simplifying the sometimes overly-complex form of expressions, INTERCAL allows
a spark-spot combination ('.) to be replaced with a wow (!). Thus '.1~.2'
is equivalent to !1~.2', and 'V.1c.2' is equivalent to "V!1c.2'".
Combining a rabbit-ears with a spot to form a rabbit (".) is not permitted,
although the programmer is free to use it should he find an EBCDIC reader
which will properly translate a 12-3-7-8 punch.
Sparks and/or rabbit-ears must also be used to distinguish among such
otherwise ambiguous subscripted and multiply-subscripted expressions as:
,1 SUB #1 ~ #2
,1 SUB ,2 SUB #1 #2 #3
,1 SUB " ,2 SUB " ,3 SUB #1 " #2 " " #3 "
The third case may be isolated into either of its possible interpretations
by simply changing some pairs of rabbit-ears to sparks, instead of adding
more ears (which would only confuse the issue further). Ambiguous cases are
defined as those for which the compiler being used finds a legitimate
interpretation which is different from that which the user had in mind. See
also section 8.1.
4. STATEMENTS
In this section is described the format of INTERCAL statements.
4.1 GENERAL FORMAT
Statements may be entered in 'free format'. That is, more than one statement
may occur on a single card, and a statement may begin on one card and end
on a later one. Note that if this is done, all intervening cards and portions
thereof must be part of the same statement. That this restriction is necessary
is immediately apparent from the following example of what might occur if
statements could be interlaced.
DO .1 <- ".1c/'&:51~"#V1c!12~;&75SUB"V'V.1~
DO .2 <- '"!1c/"&';V79SUB",&7SUB:173"'~!V9c
.2'c,&1SUB:5~#33578"'"'"~'#65535c/"V'V#&85'"'
#8196'"'~.1"c.2'~'#&5c/"'#1279c/#4351'~#65535"'
The above statements are obviously meaningless. (For that matter, so are
the statements
DO .1 <- ".1c/"&:51~"#V1c!12~;&75SUB"V'V.1~
.2'C,&1SUB:5~/333578"'"'"~#65535c/"V'V#&85'"'
DO .2 <- '"!1c/"&';V79SUB",&7SUB:173"'~!V9c
#8196'"'~.1"c.2'~'#&5c/"'#1279c!4351'~#65535"'
but this is not of interest here.)
Spaces may be used freely to enhance program legibility (or at least reduce
program illegibility), with the restriction that no word of a statement
identifier (see section 4.3) may contain any spaces.
4.2 LABELS
A statement may begin with a LOGICAL LINE LABEL enclosed in wax-wane pairs
(()). A statement may not have more than one label, although it is possible
to omit the label entirely. A line label is any integer from 1 to 65535,
which must be unique within each program. The user is cautioned, however,
that many line labels between 1000 and 1999 are used in the INTERCAL System
Library functions.
4.3 IDENTIFIERS AND QUALIFIERS
After the line label (if any), must follow one of the following statement
identifiers: DO, PLEASE, or PLEASE DO. These may be used interchangeably to
improve the aesthetics of the program. The identifier is then followed by
either, neither, or both of the following optional parameters (qualifiers):
(1) either of the character strings NOT or N'T, which causes the statement
to be automatically abstained from (see section 4.4.9) when execution
begins, and (2) a number between 0 and 100, preceded by a double-oh-seven
(%), which causes the statement to have only the specified percent chance
of being executed each time it is encountered in the course of execution.
4.4 STATEMENTS
Following the qualifiers (or, if none are used, the identifier) must occur
one of the 13 valid operations. (Exception: see section 4.5.) These are
described individually in sections 4.4.1 through 4.4.13.
4.4.1 CALCULATE
The INTERCAL equivalent of the half-mesh (=) in FORTRAN, BASIC, PL/I, and
others, is represented by an angle (<) followed by a worm (-). This
combination is read 'gets'. 32-bit variables may be assigned 16-bit values,
which are padded on the left with 16 zero bits. 16-bit variables may be
assigned 32-bit values only if the value is less than 65535. Thus, to
invert the least significant bit of the first element of 16-bit
2-dimensional array number 1, one could write:
,1SUB#1#1 <- 'V,1SUB#1#1c/#1'~'#0c/#65535'
Similarly to SNOBOL and SPITBOL, INTERCAL uses the angle-worm to define the
dimensions of arrays. An example will probably best describe the format.
To define 32-bit array number 7 as 3-dimensional, the first dimension being
seven, the second being the current value of 16-bit variable number seven,
and the third being the current value of the seventh element of 16-bit array
number seven (which is one-dimensional) mingled with the last three bits of
32-bit variable number seven, one would write (just before they came to take
him away):
;7 <- #7 BY .7 BY ",7SUB#7"c/':7~#7'
This is, of course, different from the statement:
;7 <- #7 BY .7 BY ,7SUB"#7c/':7~#7'"
INTERCAL also permits the redefining of array dimensioning, which is done
the same way as is the initial dimensioning. All values of items in an array
are lost upon redimensioning, unless they have been STASHed (see section
4.4.5), in which case restoring them also restores the old dimensions.
4.4.2 NEXT
The NEXT statement is used both for subroutine calls and for unconditional
transfers. This statement takes the form:
DO (label) NEXT
(or, of course,
PLEASE DO (label) NEXT
etc.), where (label) represents any logical line label which appears in the
program. The effect of such a statement is to transfer control to the
statement specified, and to store in a push down list (which is initially
empty) the location from which the transfer takes place. Items may be
removed from this list and may be discarded or used to return to the
statement immediately following the NEXT statement. These operations are
described in sections 4.4.3 and 4.4.4 respectively. The programmer is
generally advised to discard any stack entries which he does not intend to
utilize, since the stack has a maximum depth of 79 entries. A program's
attempting to initiate an 80th level of NEXTing will result on the fatal
error message, "PROGRAM HAS DISAPPEARED INTO THE BLACK LAGOON."
4.4.3 FORGET
The statement PLEASE FORGET exp, where exp represents any expression
(except colloquial and facial expressions), causes the expression to be
evaluated, and the specified number of entries to be removed from the
NEXTing stack and discarded. An attempt to FORGET more levels of NEXTing
than are currently stacked will cause the stack to be emptied, and no error
condition is indicated. This is because the condition is not considered to
be an error. As described in section 4.4.2, it is good programming practice
to execute a DO FORGET #1 after using a NEXT statement as an unconditional
transfer, so that the stack does not get cluttered up with unused entries:
DO (123) NEXT
.
.
(123) DO FORGET #1
4.4.4 RESUME
The statement PLEASE RESUME exp has the same effect as FORGET, except that
program control is returned to the statement immediately following the NEXT
statement which stored in the stack the last entry to be removed. Note that
a rough equivalent of the FORTRAN computed GO TO and BASIC ON exp GO TO is
performed by a sequence of the form:
DO (1) NEXT
.
.
(1) DO (2) NEXT
PLEASE FORGET #1
.
.
(2) DO RESUME .1
Unlike the FORGET statement, an attempt to RESUME more levels of NEXTing than
been stacked will cause program termination. See also section 4.4.11.
4.4.5 STASH
Since subroutines are not explicitly implemented in INTERCAL, the NEXT and
RESUME statements must be used to execute common routines. However, as
these routines might use the same variables as the main program, it is
necessary for them to save the values of any variables whose values they
alter, and later restore them. This process is simplified by the STASH
state ment, which has the form DO STASH list, where list represents a
string of one or more variable or array names, separated by intersections
(+). Thus
PLEASE STASH .123+:123+,123
stashes the values of two variables and one entire array. The values are
left intact, and copies thereof are saved for later retrieval by (what else?)
the RETRIEVE statement (see section 4.4.6). It is not possible to STASH
single array items.
4.4.6 RETRIEVE
PLEASE RETRIEVE list restores the previously STASHed values of the variables
and arrays named in the list. If a value has been stashed more than once,
the most recently STASHed values are RETRIEVEd, and a second RETRIEVE will
restore the second most recent values STASHed. Attempting to RETRIEVE a
value which has not been STASHed will result in the error message, "THROW
STICK BEFORE RETRIEVING."
4.4.7 IGNORE
The statement DO IGNORE list causes all subsequent statements to have no
effect upon variables and/or arrays named in the list. Thus, for example,
after the sequence
DO .1 <- #1
PLEASE IGNORE .1
DO .1 <- #0
16-bit variable number 1 would have the value 1, not 0. Inputting (see
section 4.4.12) into an IGNOREd variable also has no effect. The condition
is annulled via the REMEMBER statement (see section 4.4.8). Note that, when
a variable is being IGNOREd, its value, though immutable, is still
available for use in expressions and the like.
4.4.8 REMEMBER
PLEASE REMEMBER list terminates the effect of the IGNORE statement for all
variables and/or arrays named in the list. It does not matter if a variable
has been IGNOREd more than once, nor is it an error if the variable has not
been IGNOREd at all.
4.4.9 ABSTAIN
INTERCAL contains no simple equivalent to an IF statement or computed GO
TO, making it difficult to combine similar sections of code into a single
routine which occasionally skips around certain statements. The IGNORE
statement (see section 4.4.7) is helpful in some cases, but a more viable
method is often required. In keeping with the goal of INTERCAL having
nothing in common with any other language, this is made possible via the
ABSTAIN statement.
This statement takes on one of two forms. It may not take on both at any one
time. DO ABSTAIN FROM (label) causes the statement whose logical line label
is (label) to be abstained form. PLEASE ABSTAIN FROM gerund list causes all
statements of the specified type(s) to be abstained from, as in
PLEASE ABSTAIN FROM STASHING
PLEASE ABSTAIN FROM IGNORING + FORGETTING
PLEASE ABSTAIN FROM NEXTING
or PLEASE ABSTAIN FROM CALCULATING
Statements may also be automatically abstained from at the start of
execution via the NOT or N'T parameter (see section 4.3).
If, in the course of execution, a statement is encountered which is being
abstained from, it is ignored and control passes to the next statement in
the program (unless it, too, is being abstained from).
The statement DO ABSTAIN FROM ABSTAINING is perfectly valid, as is DO ABSTAIN
FROM REINSTATING (although this latter is not usually recommended). However,
the statement DO ABSTAIN FROM GIVING UP is not accepted, even though DON'T
GIVE UP is.
4.4.10 REINSTATE
The REINSTATE statement, like the ABSTAIN, takes as an argument either a
line label or a gerund list. No other form of argument is permitted. For
example, the following is an invalid argument:
Given: x=/0, y=/0, Prove: x+y=0
Since x=/0, then x+1=/1, x+a=/a, x+y=/y.
Thus x+y =/ anything but 0.
Since x+y cannot equal anything but 0, x+y=0.
Q.E.D.
REINSTATEment nullifies the effects of an abstention. Either form of
REINSTATEment can be used to "free" a statement, regardless of whether the
statement was abstained from by gerund list, line label, or NOT. Thus,
PLEASE REINSTATE REINSTATING is not necessarily an irrelevant statement,
since it might free a DON'T REINSTATE command or a REINSTATE the line label
of which was abstained from. However, DO REINSTATE GIVING UP is invalid,
and attempting to REINSTATE a GIVE UP statement by line label will have no
effect. Note that this insures that DON'T GIVE UP will always be a
"do-nothing" statement.
4.4.11 GIVE UP
PLEASE GIVE UP is used to exit from a program. It has the effect of a PLEASE
RESUME #80. DON'T GIVE UP, as noted in section 4.4.10, is effectively a null
statement.
4.4.12 Input
Input is accomplished with the statement DO WRITE IN list, where list
represents a string of variables and/or elements or arrays, separated by
intersections. Numbers are represented on cards, each number on a separate
card, by spelling out each digit (in English) and separating the digits
with one or more spaces. A zero (0) may be spelled as either ZERO or OH.
Thus the range of (32-bit) input values permissible extends from ZERO (or
OH) through FOUR TWO NINE FOUR NINE SIX SEVEN TWO NINE FIVE.
Attempting to write in a value greater than or equal to SIX FIVE FIVE THREE
SIX for a 16-bit variable will result in the error message, "DON'T BYTE OFF
MORE THAN YOU CAN CHEW."
4.4.13 Output
Values may be output to the printer, one value per line, via the statement
DO READ OUT list, where the list contains variables, array elements, and/or
constants. Output is in the form of "extended" Roman numerals (also called
_
"butchered" Roman numerals), with an overline ( ) indicating the value below
is "times 1000", and lower-case letters indicating "times 1000000". Zero
is indicated by an overline with no character underneath. Thus, the range
_ __ _______
of (32-bit) output values possible is from through ivccxcivCMLXVIICCXCV.
Note: For values whose residues modulo 1000000 are less than 4000, M is
used to represent 1000; for values whose residues are 4000 or greater, I is
__
used. Thus #3999 would read out as MMMIM while #4000 would read out as IV.
_ _ _
Similar rules apply to the use of M and i for 1000000, and to that of m and i
for 1000000000.
4.5 Comments
Unrecognizable statements, as noted in section 7, are flagged with a splat
(*) during compilation, and are not considered fatal errors unless they
are encountered during execution, at which time the statement (as input at
compilation time) is printed and execution is terminated. This allows for
an interesting (and, by necessity, unique) means of including comments in
an INTERCAL listing. For example, the statement:
* PLEASE NOTE THAT THIS LINE HAS NO EFFECT
will be ignored during execution due to the inclusion of the NOT qualifier.
User-supplied error messages are also easy to implement:
* DO SOMETHING ABOUT OVERFLOW IN ;3
as are certain simple conditional errors:
* (123) DON'T YOU REALIZE THIS STATEMENT SHOULD ONLY BE ENCOUNTERED
ONCE?
PLEASE REINSTATE (123)
This pair of statements will cause an error exit the second time they are
encountered. Caution!! The appearance of a statement identifier in an
intended comment will be taken as the beginning of a new statement. Thus,
the first example on the preceding page could not have been:
* PLEASE NOTE THAT THIS LINE DOES NOTHING
The third example, however, is valid, despite the appearance of two cases
of D-space-O, since INTERCAL does not ignore extraneous spaces in statement
identifiers.
5. SUBROUTINE LIBRARY
INTERCAL provides several built-in subroutines to which control can be
transferred to perform various operations. These operations include many
useful functions which are not easily representable in INTERCAL, such as
addition, subtraction, etc.
5.1 Usage
In general, the operands are .1, .2, etc., or :1, :2, etc., and the result(s)
are stored in what would have been the next operand(s). For instance, one
routine adds .1 to .2 and store the sum in .3, with .4 being used to indicate
overflow. All variables not used for results are left unchanged.
5.2 Available Functions
At the time of this writing, only the most fundamental operations are offered
in the library, as a more complete selection would require prohibitive time
and coree to implement. These functions, along with their corresponding entry
points (entered via DO (entry) NEXT) are listed below.
(1000) .3 <- .1 plus .2, error exit on overflow
(1009) .3 <- .1 plus .2
.4 <- #1 if no overflow, else .4 <- #2
(1010) .3 <- .1 minus .2, no action on overflow
(1020) .1 <- .1 plus #1, no action on overflow
(1030) .3 <- .1 times .2, error exit on overflow
(1039) .3 <- .1 times .2
.4 <- #1 if no overflow, else .4 <- #2
(1040) .3 <- .1 divided by .2
.3 <- #0 if .2 is #0
(1050) .2 <- :1 divided by .1, error exit on overflow
.2 <- #0 if .1 is #0
(1500) :3 <- :1 plus :2, error exit on overflow
(1509) :3 <- :1 plus :2
:4 <- #1 if no overflow, else :4 <- #2
(1510) :3 <- :1 minus :2, no action on overflow
(1520) :1 <- .1 concatenated with .2
(1525) This subroutine is intended solely for internal
use within the subroutine library and is therefore
not described here. Its effect is to shift .3
logically 8 bits to the left.
(1530) :1 <- .1 times .2
(1540) :3 <- :1 times :2, error exit on overflow
(1549) :3 <- :1 times :2
:4 <- #1 if no overflow, else :4 <- #2
(1550) :3 <- :1 divided by :2
:3 <- #0 if :2 is #0
(1900) .1 <- uniform random no. from #1 to #65535
(1910) .2 <- normal random no. from #0 to .1, with
standard deviation .1 divided by #12
6. PROGRAMMING HINTS
For the user looking to become more familiar with the INTERCAL language, we
present in this section an analysis of a complex program, as well as some
suggested projects for the ambitious programmer.
Considering the effort involved in writing an INTERCAL program, it was
decided in putting together this manual to use an already existing program
for instructive analysis. Since there was only one such program available,
we have proceeded to use it. It is known as the "INTERCAL System Library."
6.1 Description
The program listing begins on the second page following. It is in the same
format as would be produced by the Princeton INTERCAL compiler in FORMAT
mode with WIDTH=62 (see section 8). For a description of the functions
performed by the Library, see section 5.2.
6.2 Analysis
We shall not attempt to discuss here the algorithms used, but rather we
shall point out some of the general techniques applicable to a wide range
of problems.
Statements 10, 14, 15, and 26 make up a virtual "computed GO TO". When
statement 10 is executed, control passes eventually to statement 16 or 11,
depending on whether .5 contains #1 or #2, respectively. The value of .5
is determined in statement 9, which demonstrates another handy technique.
To turn an expression, exp, with value #0 or #1, into #1 or #2 (for use in
a "GO TO"), use "V-'exp'c/#1"~#3. To reverse the condition (i.e., convert #0
to #2 and leave #1 alone) use "V-'exp'c/#2"~#3.
Certain conditions are easily checked. For example, to test for zero,
select the value from itself and select the bottom bit (see statement 54).
To test for all bits being 1's, select the value from itself and select the
top bit (see statement 261). The test for greater than, performed in
statements 192 and 193 on 32-bit values, employs binary logical operations,
which are performed as follows:
'V.1c.2'~'#0c/#65535'
for 16-bit values or, for 32-bit values:
"'V":1~'#65535c30'"c/":2~'#65535c/#0'"'~'#0
c/#65535'"c/"'V":1~'#0c/#65535'"c/":2~'#0
c/#65535'"'~'#0c/#65535'"
(The proofs are left as an exercise to the reader.)
Testing for greater-than with 16-bit values is somewhat simpler and is done
with the pair of statements:
DO .C <- 'V.Ac.B'~'#0c/#65535'
DO .C <- '&"'.A~.C'~'"V'V.C~.C'c/#32768"
~"#0c/#65535"'"c/".C~.CZ''ZZZ`#1
This sets .C (a dummy variable) to #1 if .A > .B, and #0 otherwise. The
expression may be expanded as described above to instead set .C to #1 or
#2.
Note also in statement 220 the occurrence of ~"#65535c65535". Although
these operations select the entire value, they are not extraneous, as they
ensure that the forthcoming Vs will be operating on 32-bit values.
In several virtual computed GO TOs the DO FORGET #1 (statement 15 in the
earlier example) has been omitted, since the next transfer of control would
be a DO RESUME #1. By making this a DO RESUME #2 instead, the FORGET may
be forgotten.
In statement 64, note that .2 is STASHed twice by a single statement. This
is perfectly legal.
Lastly, note in statements 243 and 214 respectively, expressions for
shifting 16- and 32-bit variables logically one place to the left.
Statement 231 demonstrates right-shifting for 32-bit variables.
MIKE GETS TO INSERT THE PROGRAM HERE!
6.3 Program Listing
1 (1000) PLEASE IGNORE .4
2 PLEASE ABSTAIN FROM (1005)
3 (1009) DO STASH .1 + .2 + .5 + .6
4 DO .4 <- #1
5 DO (1004) NEXT
6 (1004) PLEASE FORGET #1
7 DO .3 <- 'V.1c.2'~'#0c/#65535'
8 DO .6 <- '&.1c.2'~'#0c/#65535'
9 PLEASE DO .5 <- "V!6~#32768'c/#1"~#3
10 DO (1002) NEXT
11 DO .4 <- #2
12 (1005) DO (1006) NEXT
* 13 (1999) DOUBLE OR SINGLE PRECISION OVERFLOW
14 (1002) DO (1001) NEXT
15 (1006) PLEASE FORGET #1
16 DO .5 <- 'V"!6~.6'~#1"c/#1'~#3
17 DO (1003) NEXT
18 DO .1 <- .3
19 DO .2 <- !6c/#0'~'#32767c/#1'
20 DO (1004) NEXT
21 (1003) DO (1001) NEXT
22 DO REINSTATE (1005)
23 (1007) PLEASE RETRIEVE .1 + .2 + .5 + .6
24 DO REMEMBER .4
25 PLEASE RESUME #2
26 (1001) DO RESUME .5
27 (1010) DO STASH .1 + .2 + .4
28 DO .4 <- .1
29 DO .1 <- 'V.2c/#65535'~'#0c/#65535'
30 DO (1020) NEXT
31 PLEASE DO .2 <- .4
32 PLEASE DO (1009) NEXT
33 DO RETRIEVE .1 + .2 + .4
34 PLEASE RESUME #1
35 (1020) DO STASH .2 + .3
36 DO .2 <- #1
37 PLEASE DO (1021) NEXT
38 (1021) DO FORGET #1
39 DO .3 <- "V!1~.2'c/#1"~#3
40 PLEASE DO .1 <- 'V.1c.2'~'#0c/#65535'
41 DO (1022) NEXT
42 DO .2 <- !2c/#0'~'#32767c/#1'
43 DO (1021) NEXT
44 (1023) PLEASE RESUME .3
45 (1022) DO (1023) NEXT
46 PLEASE RETRIEVE .2 + .3
47 PLEASE RESUME #2
48 (1030) DO ABSTAIN FROM (1033)
49 PLEASE ABSTAIN FROM (1032)
50 (1039) DO STASH :1 + .5
51 DO (1530) NEXT
52 DO .3 <- :1~#65535
53 PLEASE DO .5 <- :1~'#65280c/#65280'
54 DO .5 <- 'V"!5~.5'~#1"c/#1'~#3
55 DO (1031) NEXT
56 (1032) DO (1033) NEXT
57 DO (1999) NEXT
58 (1031) DO (1001) NEXT
59 (1033) DO .4 <- .5
60 DO REINSTATE (1032)
61 PLEASE REINSTATE (1033)
62 DO RETRIEVE :1 + .5
63 PLEASE RESUME #2
64 (1040) PLEASE STASH .1 + .2 + .2 + :1 + :2 + :3
65 DO .2 <- #0
66 DO (1520) NEXT
67 DO STASH :1
68 PLEASE RETRIEVE .2
69 DO .1 <- .2
70 DO .2 <- #0
71 PLEASE DO (1520) NEXT
72 DO :2 <- :1
73 DO RETRIEVE .1 + .2 + :1
74 DO (1550) NEXT
75 PLEASE DO .3 <- :3
76 DO RETRIEVE :1 + :2 + :3
77 DO RESUME #1
78 (1050) PLEASE STASH :2 + :3 + .5
79 DO :2 <- .1
80 PLEASE DO (1550) NEXT
81 DO .5 <- :3~'#65280c/#65280'
82 DO .5 <- 'V"!5~.5'~#1"c/#1'~#3
83 DO (1051) NEXT
84 DO (1999) NEXT
85 (1051) DO (1001) NEXT
86 DO .2 <- :3
87 PLEASE RETRIEVE :2 + :3 + .5
88 DO RESUME #2
89 (1500) PLEASE ABSTAIN FROM (1502)
90 PLEASE ABSTAIN FROM (1506)
91 (1509) PLEASE STASH :1 + .1 + .2 + .3 + .4 + .5 + .6
92 DO .1 <- :1~#65535
93 PLEASE DO .2 <- :2~#65535
94 DO (1009) NEXT
95 DO .5 <- .3
96 PLEASE DO .6 <- .4
97 DO .1 <- :1~'#65280c/#65280'
98 DO .2 <- :2~'#65280c/#65280'
99 DO (1009) NEXT
100 DO .1 <- .3
101 PLEASE DO (1503) NEXT
102 DO .6 <- .4
103 DO .2 <- #1
104 DO (1009) NEXT
105 DO .1 <- .3
106 DO (1501) NEXT
107 (1504) PLEASE RESUME .6
108 (1503) DO (1504) NEXT
109 (1501) DO .2 <- .5
110 DO .5 <- 'V"'&.6c.4'~#1"c/#2'~#3
111 DO (1505) NEXT
112 (1506) DO (1502) NEXT
113 PLEASE DO (1999) NEXT
114 (1505) DO (1001) NEXT
115 (1502) DO :4 <- .5
116 DO (1520) NEXT
117 DO :3 <- :1
118 PLEASE RETRIEVE :1 + .1 + .2 + .3 + .4 + .5 + .6
119 DO REINSTATE (1502)
120 DO REINSTATE (1506)
121 PLEASE RESUME #3
122 (1510) DO STASH :1 + :2 + :4
123 DO :1 <- "'V/":2~'#65535c/#0'"c/#65535'~'#0c/#6553
5'"c/"'V":2~'#0c/#65535'"c/#65535'~'#0c65535
'"
124 DO :2 <- #1
125 DO (1509) NEXT
126 PLEASE RETRIEVE :1
127 DO :2 <- :3
128 PLEASE DO (1509) NEXT
129 DO RETRIEVE :2 + :4
130 PLEASE RESUME #1
131 (1520) PLEASE STASH .3 + .4
132 DO .3 <- .1~#43690
133 DO (1525) NEXT
134 PLEASE DO .4 <- 'V.3c/".2~#43690"'~'#0c/#65535'
135 DO .3 <- .1~#21845
136 PLEASE DO (1525) NEXT
137 DO :1 <- .4c/"'V.3c/".2~#21845"'~'#0c/#65535'"
138 PLEASE RETRIEVE .3 + .4
139 DO RESUME #1
140 (1525) DO .3 <- '"'"'"!3c/#0'~'#32767c/#1'"c/#0'~'#32767
c/#1'"c/#0'~'#16383c/#3'"c/#0'~'#4095c/#15'
141 PLEASE RESUME #1
142 (1530) DO STASH :2 + :3 + .3 + .5
143 DO :1 <- #0
144 DO :2 <- .2
145 DO .3 <- #1
146 DO (1535) NEXT
147 (1535) PLEASE FORGET #1
148 DO .5 <- "V!1~.3'c/#1"~#3
149 DO (1531) NEXT
150 DO (1500) NEXT
151 DO :1 <- :3
152 PLEASE DO (1533) NEXT
153 (1531) PLEASE DO (1001) NEXT
154 (1533) DO FORGET #1
155 DO .3 <- !3c/#0'~'#32767c/#1'
156 DO :2 <- ":2~'#0c/#65535'"c/"'":2~'#32767c/#0'"c/#
0'~'#32767c/#1'"
157 PLEASE DO .5 <- "V!3~.3'c/#1"~#3
158 DO (1532) NEXT
159 DO (1535) NEXT
160 (1532) DO (1001) NEXT
161 PLEASE RETRIEVE :2 + :3 + .3 + .5
162 DO RESUME #2
163 (1540) PLEASE ABSTAIN FROM (1541)
164 DO ABSTAIN FROM (1542)
165 (1549) PLEASE STASH :1 + :2 + :4 + :5 + .1 + .2 + .5
166 DO .1 <- :1~#65535
167 PLEASE DO .2 <- :2~'#65280c/#65280'
168 DO .5 <- :1~'#65280c/#65280'
169 DO (1530) NEXT
170 DO :3 <- :1
171 DO .2 <- :2~#65535
172 PLEASE DO (1530) NEXT
173 DO :5 <- :1
174 DO .1 <- .5
175 DO (1530) NEXT
176 DO :4 <- :1
177 PLEASE DO :1 <- ":3~'#65280c/#65280'"c/":5~'652
80c/#65280'"
178 DO .5 <- ':1~:1'~#1
179 DO .2 <- :2~'#65280c/#65280'
180 DO (1530) NEXT
181 PLEASE DO .5 <- '"':1~:1'~#1"c.5'~#3
182 DO .1 <- :3~#65535
183 DO .2 <- #0
184 DO (1520) NEXT
185 PLEASE DO :2 <- :1
186 PLEASE DO .1 <- :4~#65535
187 DO (1520) NEXT
188 DO (1509) NEXT
189 DO .5 <- !5c/":4~#3"'~#15
190 DO :1 <- :3
191 DO :2 <- :5
192 DO (1509) NEXT
193 PLEASE DO .5 <- !5c/"4~#3"'~#63
194 DO .5 <- 'V"!5~.5'~#1"c/#1'~#3
195 PLEASE RETRIEVE :4
196 (1541) DO :4 <- .5
197 DO (1543) NEXT
198 (1542) DO (1544) NEXT
199 PLEASE DO (1999) NEXT
200 (1543) DO (1001) NEXT
201 (1544) DO REINSTATE (1541)
202 PLEASE REINSTATE (1542)
203 PLEASE RETRIEVE :1 + :2 + :5 + .1 + .2 + .5
204 DO RESUME #2
205 (1550) DO STASH :1 + :4 + :5 + .5
206 DO :3 <- #0
207 DO .5 <- 'V"':2~:2'~#1"c/#1'~#3
208 PLEASE DO (1551) NEXT
6.4 Programming Suggestions
For the novice INTERCAL programmer, we provide here a list of suggested
INTERCAL programming projects:
Write an integer exponentiation subroutine. :1 <- .1 raised to the .2 power.
Write a double-precision sorting subroutine. Given 32-bit array ;1 of size
:1, sort the contents into numerically increasing order, leaving the results
in ;1.
Generate a table of prime numbers.
Put together a floating-point library, using 32-bit variables to represent
floating-point numbers (let the upper half be the mantissa and the lower
half be the characteristic). The library should be capable of performing
floating-point addition, subtraction, multiplication, and division, as well
as the natural logarithm function.
Program a Fast Fourier Transform (FFT). This project would probably entail
the writing of the floating-point library as well as sine and cosine functions.
Calculate, to :1 places, the value of pi.
7. ERROR MESSAGES
Due to INTERCAL's implementation of comment lines (see section 4.5), most
error messages are produced during execution instead of during compilation.
All errors except those not causing immediate termination of program execution
are treated as fatal.
7.1 Format
All error messages appear in the following form:
ICLnnnI (error message)
ON THE WAY TO STATEMENT nnnn
CORRECT SOURCE AND RESUBMIT
The message varies depending upon the error involved. For undecodable
statements the message is the statement itself. The second line tells
which statement would have been executed next had the error not occurred.
Note that if the error is due to 80 attempted levels of NEXTing, the
statement which would have been executed next need not be anywhere near the
statement causing the error.
7.2 Messages
Brief descriptions of the different error types are listed below according
to message number.
000 An undecodable statement has been encountered in the course of
execution. Note that keypunching errors can be slightly disastrous,
since if 'FORGET' were misspelled F-O-R-G-E-R, the results would
probably not be those desired. Extreme misspellings may have even
more surprising consequences. For example, misspelling 'FORGET'
R-E-S-U-M-E could have drastic results.
017 An expression contains a syntax error.
079 Improper use has been made of statement identifiers.
099 Improper use has been made of statement identifiers.
123 Program has attempted 80 levels of NEXTing.
129 Program has attempted to transfer to a non-existent line label.
139 An ABSTAIN or REINSTATE statement references a non-existent line label.
182 A line label has been multiply defined.
197 An invalid line label has been encountered.
200 An expression involves an unidentified variable.
240 An attempt has been made to give an array a dimension of zero.
241 Invalid dimensioning information was supplied in defining or using
an array.
275 A 32-bit value has been assigned to a 16-bit variable.
436 A retrieval has been attempted for an unSTASHed value.
533 A WRITE IN statement or interleave (c) operation has produced a
value requiring over 32 bits to represent.
562 Insufficient data.
579 Input data is invalid.
621 The expression of a RESUME statement evaluated to #0.
632 Program execution was terminated via a RESUME statement instead of
GIVE UP.
633 Execution has passed beyond the last statement of the program.
774 A compiler error has occurred (see section 8.1).
778 An unexplainable compiler error has occurred (see J. Lyon or B. Woods).
[3]
TONSIL A
The Official INTERCAL Character Set
Tabulated on page XX are all the characters used in INTERCAL, excepting
letters and digits, along with their names and interpretations. Also
included are several characters not used in INTERCAL, which are presented
for completeness and to allow for future expansion.
_____________________
3) Since all other reference manuals have Appendices, it was decided that
the INTERCAL manual should contain some other type of removable organ.
4) This footnote intentionally unreferenced.
_______________________________________________________________________
| |
|Character Name Use (if any) |
| |
| . spot identify 16-bit variable |
| : two-spot identify 32-bit variable |
| , tail identify 16-bit array |
| ; hybrid identify 32-bit array |
| # mesh identify constant |
| = half-mesh |
| ' spark grouper |
| ` backspark |
| ! wow equivalent to spark-spot |
| ? what unary exlusive OR (ASCII) |
| " rabbit-ears grouper |
| ". rabbit equivalent to ears-spot |
| | spike |
| % double-oh-seven percentage qualifier |
| - worm used with angles |
| < angle used with worms |
| > right angle |
| ( wax precedes line label |
| ) wane follows line label |
| [ U turn |
| ] U turn back |
| { embrace |
| } bracelet |
| * splat flags invalid statements |
| & ampersand[5] unary logical AND |
| V V unary logical OR |
| (or book) |
| V- bookworm unary exclusive OR |
| (or universal qualifier) |
| $ big money unary exclusive OR (ASCII) | |
| c| change binary mingle |
| ~ sqiggle binary select |
| _ flat worm |
| overline indicates "times 1000" |
| + intersection separates list items |
| / slat |
| \ backslat |
| @ whirlpool |
| -' hookworm |
| ^ shark |
| (or simply sharkfin) |
| #I[] blotch |
|_____________________________________________________________________|
Table 2 (top view). INTERCAL character set.
__________________________________
5) Got any better ideas?
NOTES ON THE ATARI IMPLEMENTATION
The Atari implementation of INTERCAL differs from the original Princeton
version primarily in the use of ASCII rather than EBCDIC. Since there is no
"change" sign (c) in ASCII, we have substituted the "big money" ($) as the
mingle operator. We feel that this correctly represents the increasing cost
of software in relation to hardware. (Consider that in 1970 one could get
RUNOFF for free, to run on a $20K machine, whereas today a not quite as
powerful formatter costs $99 and runs on a $75 machine.) We also feel that
there should be no defensible contention that INTERCAL has any sense.
Also, since overpunches are difficult to read on the average VDT, the
exclusive-or operator may be written ?. This correctly expresses the
average person's reaction on first encountering exclusive-or, especially on
a PDP-11. Note that in both of these cases, the over-punched symbol may
also be used if one is masochistic, or concerned with portability to the
Princeton compiler. The correct over-punch for "change" is "c/"
and the correct over-punch for V is "V-". These codes will be
properly printed if you have a proper printer, and the corresponding EBCDIC
code will be produced by the /IBM option on the LIST command.