SCELBAL
SCELBAL, short for SCientific ELementary BAsic Language, is a version of the
The language was published in book form, with introductory sections followed by
History
The primary author of SCELBAL is Mark Arnold, who was a high-school student in 1974 when the SCELBI was announced. Arnold was friends with professors at the University of Wyoming (UW), and through them had arranged to have an account on their Sigma 7 mainframe computer. The first version of what became SCELBAL was written for this machine. Later that year, he wrote an 8008 cross compiler on that platform.
Arnold entered UW in 1975 and contacted Nat Wadsworth, one of the founders of SCELBI, pitching the idea of a
It took Wadsworth several months to finally arrange a contract, which included sending Arnold an 8B development system. This significantly delayed the release of the language into 1976. Arnold speculated that, lacking these delays, SCELBAL could have been released at about the same time as Altair BASIC in late 1975. It was first presented in a lengthy article in the second issue of Dr. Dobb's Journal in February 1976.[1]
The release of SCLEBAL was announced in an advertisement in
Description
SCELBAL used a 32-bit (four byte)
SCELBAL was otherwise similar to other BASIC dialects, including early MS versions like Altair BASIC, lacking string variables and operators and a number of mathematic functions. Other differences were less pronounced. The IF
statement had an optional form IF...GOTO
that removed the need for THEN
, IF X<Y GOTO 100
.[6] It also retained the MS-style short form for the same concept, IF X<Y THEN 100
. It also allowed conditional execution of other statements, such as IF X<Y THEN PRINT X
. [7]
The base language did not support string handling, although literal (constant) strings could be used in PRINT
, and had the supporting functions of CHR
to print non-printable characters, and TAB
to provide layout. Oddly, the system required ASCII codes to have the high-bit set, so to convert from normal ASCII to SCELBI character codes, one had to add or subtract 128. For instance,
PRINT "HELLO";CHR(172);CHR(160);"WORLD"
to produce the string "HELLO, WORLD" in the output.[8]
INPUT
would normally read the user-entered text as a number, but allowed the dollar sign to indicate the value should be read as the SCELBI code instead. For instance, INPUT A
would read the user input "1" into A as the floating-point value 1, while INPUT A$
would result in A being set to 177, 49 (ASCII for "1") + 128. Additionally, when the dollar sign is used, the traditional "?" prompt is not printed, and command returned to the language as soon as a single character is entered, instead of waiting for the carriage return as in the normal case.[8]
Among the few other differences was that the NEW
command found in MS, which clears out existing program code and data, is called SCR
for "scratch",
Error codes were reduced to two letters, and code for LOAD
and SAVE
were provided in boilerplate form and expected to be implemented when ported to different platforms.[12] Line numbers could be between 1 and 999999,[10] whereas most BASICs used a 16-bit integer and thus supported lines from 1 to 32767 or 1 to 65535.
Language features
- Taken from the 1976 manual unless otherwise noted.[13]
Commands
Immediate-mode only
Referred to as "executive" mode in the documentation.
SCR
- scratch, equivalent to MS
NEW
LIST
RUN
LOAD
SAVE
Immediate or program mode
PRINT
INPUT
- Like MS, could accept multiple variables,
INPUT A,B,C
. Did not include a prompt string. LET
- Like MS, the
LET
was optional, so15 LET X=10
and15 X=10
are equivalent. IF...THEN
IF...GOTO
- Alternate form of
IF...THEN
. GOTO
- It appears the "spaced version",
GO TO
, was not supported. GOSUB...RETURN
FOR...TO...STEP...NEXT
- As in MS,
STEP
is optional and assumed to be 1.NEXT
required a variable, unlike later MS versions. REM
END
DIM
- Arrays worked as in MS, but were optional and could be turned off to save memory. Only single-dimension arrays were supported, and the total number of elements for all arrays combined was 64 numbers.
Functions
INT
SGN
ABS
SQR
RND
- As in MS, takes a dummy variable and returns a value between 0 and 1.
CHR
- Note the lack of the $ found in MS, which uses
CHR$
. TAB
UDF
Extensions
SCELBI published two extensions to the system, the Mathematical Functions Supplement, and the Strings Supplement.
Math Functions Supplement
The Mathematical Functions Supplement added five new transcendental functions, SIN
, COS
, EXP
, LOG
, and ATN
.[14]
String Supplement
The String Supplement was somewhat larger than the Math Functions, including a number of new features.
Strings could be up to 80 characters long, and the system could hold a total of 64 string variables. Any one of those 64, or all of them, could be one-dimensional arrays, but the total number still had to be 64 strings in total. Oddly, string arrays did not require a DIM
statement.[15]
In contrast to MS BASIC, and the
LEFT$
, RIGHT$
, MID$
to access substrings, the array-access syntax was used with a colon preceding the starting point and optionally a semicolon preceding the length. As SCELBAL also supported string arrays, the first number in the array accessors was the array index, and was optional if the variable was not an array. So, for instance, the code:[15]10 LET A$="HELLO"
20 PRINT A$(:2;3)
would result in "ELL" being printed to the output. If an array was used the syntax required the array index in the first parameter:[15]
100 LET A$(1)="HELLO"
150 LET A$(2)="WORLD"
200 PRINT A$(2:2;3)
would result in "ORL" being printed to the output. SCELBAL also allowed omitting the semicolon, which specifies the characters from the starting point to the end of the string. So, for instance, the code:
210 PRINT A$(2:2)
would result in "ORLD" being printed to the output.
Although similar to SDS BASIC, there is a major difference in the way this works in comparison to the other BASICs that used slicing syntax, in that the last parameter is the length, not a position. For instance, in Atari BASIC the similar-looking code:[16]
20 PRINT A$(2,3)
would instead output "EL", as the instruction translates to "print all characters between positions 2 and 3". In this fashion, SCELBAL works in a fashion more similar to MS BASIC, where the equivalents would be:[17]
20 PRINT MID$(A$,2,3)
and
210 PRINT RIGHT$(A$(2),2)
To add full support for strings, the Supplement replaced the original CHR
with CHR$
, which matched the syntax of its MS counterpart.[15] Likewise, INPUT
was modified so string variables worked like numeric ones, waiting for the carriage return and then assigning the entire user input to the associated string variable.[18] It also added the support functions LEN
and ASC
,[15] and VAL$
to convert a string containing a numeric value to a string representation of that number. As in MS, concatenation used the +
operator.[18]
References
Citations
- ^ Arnold, Mark; Wadsworth, Nat (February 1976). "SCELBAL - A Higher Level Language for 8008/8080 Systems". Dr. Dobb's Journal. pp. 30–53.
- ^ "Shocking!". Byte. June 1976. p. 47.
- ^ Arnold & Wadsworth 1976, p. 10.1.
- ^ Arnold & Wadsworth 1976, p. 10.
- ^ Steil, Michael (20 October 2008). "Create your own Version of Microsoft BASIC for 6502".
- ^ Arnold & Wadsworth 1976, p. 14.10.
- ^ Arnold & Wadsworth 1976, p. 2.3.
- ^ a b Arnold & Wadsworth 1976, p. 14.16.
- ^ Arnold & Wadsworth 1976, p. 14.1.
- ^ a b Arnold & Wadsworth 1976, p. 14.17.
- ^ Arnold & Wadsworth 1976, p. 14.3.
- ^ Arnold & Wadsworth 1976, p. 14.18.
- ^ Arnold & Wadsworth 1976.
- ^ Math 1977, p. 1.
- ^ a b c d e Strings 1977, p. 1.
- ^ Small, David, ed. (1983). "Atari Strings and Text Handling". The Creative Atari. Creative Computing.
- ^ Strings 1977, p. 3.
- ^ a b Strings 1977, p. 2.
Bibliography
- Arnold, Mark; Wadsworth, Nat (1976). SCELBAL: A higher level language for 8008/8080 systems (PDF). SCELBI Computer Consulting.
- Arnold, Mark (1977). SCELBAL Mathematical Functions Supplement. SCELBI Computer Consulting.
- Arnold, Mark (1977). SCELBAL Strings Supplement. SCELBI Computer Consulting.