Paradigm Imperative | License Proprietary | |
Designed by John Grant, Steve Vickers Developer Nine Tiles Networks,
Sinclair Research First appeared 1979; 38 years ago (1979) Platform ZX80, ZX81, ZX Spectrum | ||
Sinclair BASIC is a dialect of the programming language BASIC used in the 8-bit home computers from Sinclair Research and Timex Sinclair. The Sinclair BASIC interpreter was made by Nine Tiles Networks Ltd.
Contents
History
Sinclair BASIC was originally developed in 1979 for the ZX80 by Nine Tiles. The programmers were John Grant, the owner of Nine Tiles, and Steve Vickers.
It was initially an incomplete implementation of the 1978 American National Standards Institute (ANSI) minimal BASIC standard with integer arithmetic only, termed the 4K BASIC (for its ROM size) for the ZX80. It evolved through the floating-point 8K BASIC for the ZX81 and TS1000 (which was also available as an upgrade for the ZX80), and became an almost complete version in the 16 KB ROM ZX Spectrum. It is present in all ZX Spectrum compatibles.
As of 2015, interpreters exist for modern operating systems, and older systems, that allow Sinclair Basic to be used easily.
Syntax
New BASIC programmers might start with a simple program, perhaps using the language's PRINT statement to display a message on the screen; a well-known and often-replicated example is Kernighan and Ritchie's Hello world program:
Keywords
On the 16K/48K ZX Spectrum, there are 88 keywords in Sinclair BASIC, denoting commands (of which there were 51), functions and logical operators (32), and other keywords (5):
BEEP, BIN, BORDER, BRIGHT, CAT, CIRCLE, CLEAR, CLOSE #, CLS, CONTINUE, COPY, DATA, DEF FN, DIM, DRAW, ERASE, FLASH, FORMAT, FOR, GO SUB, GO TO, IF, INK, INPUT, INVERSE, LET, LIST, LLIST, LOAD, LPRINT, MERGE, MOVE, NEW, NEXT, OPEN #, OUT, OVER, PAPER, PAUSE, PLOT, POKE, PRINT, RANDOMIZE, READ, REM, RESTORE, RETURN, RUN, SAVE, STOP, VERIFY
ABS, ACS, AND, ASN, ATN, ATTR, CHR$, CODE, COS, EXP, FN, INKEY$, INT, IN, LEN, LN, NOT, OR, PEEK, PI, POINT, RND, SCREEN$, SGN, SIN, SQR, STR$, TAN, TO, USR, VAL, VAL$,
AT, LINE, STEP, TAB, THEN
They are entered via Sinclair's unique keyword entry system. The most common commands need one keystroke only; for example, pressing only P at the start of a line on a Spectrum produces the full command PRINT. Less frequent commands require more complex key sequences: BEEP (for example) is keyed by pressing CAPS SHIFT plus SYMBOL SHIFT to access extended mode (later models include an EXTENDED MODE key), keeping SYMBOL SHIFT held down and pressing Z. Keywords are color-coded on the original Spectrum keyboard to indicate which mode is required.
The ZX81 8K BASIC used the shorter forms GOTO, GOSUB, CONT and RAND, whereas the Spectrum used the longer forms GO TO, GO SUB, CONTINUE and RANDOMIZE. The ZX80 4K BASIC also used these longer forms but with differed by using the spelling RANDOMISE. The ZX81 8K BASIC was the only version to use FAST, SCROLL, SLOW and UNPLOT. The ZX80 4K BASIC had the exclusive function TL$(); it was equivalent to the string operator ( TO ) in later versions.
Unique code points are assigned in the ZX80 character set, ZX81 character set and ZX Spectrum character set for each keyword or multi-character operator, i.e. <=, >=, <>, "" (tokenized on the ZX81 only), ** (replaced with ↑ on the Spectrum). These are expanded by referencing a token table in ROM. Thus, a keyword uses one byte of memory only, a significant saving over traditional letter-by-letter storage. This also meant that the BASIC interpreter could quickly determine any command or function by evaluating one byte, and that the keywords need not be reserved words like in other BASIC dialects or other programming languages, e.g., it is allowed to define a variable named PRINT and output its value with PRINT PRINT. This is also related to the syntax requirement that every line start with a command keyword, and pressing the one keypress for that command at the start of a line changes the editor from command mode to letter mode. Thus, variable assignment requires LET (i.e., LET a=1 not only a=1). This practice is also different from other BASIC dialects. Further, it meant that unlike other BASIC dialects, the interpreter needed no parentheses to identify functions; SIN x was sufficient, no SIN(x) needed (though the latter was allowed). The 4K BASIC ROM of the ZX80 had a short list of exceptions to this: the functions CHR$(), STR$(), TL$(), PEEK(), CODE(), RND(), USR() and ABS() did not have one-byte tokens but were typed in letter-by-letter and required the parentheses. They were listed as the INTEGRAL FUNCTIONS on a label above and to the right of the keyboard.
The 128K Spectrum models, the ZX Spectrum 128, +2, +3, +2A, and +2B, also stored keywords internally in one-byte code points, but used a conventional letter-by-letter BASIC input system. They also introduced two new commands:
PLAY, which operated the 128k models' General Instrument AY-3-8910 music chipSPECTRUM, which switched the 128k Spectrum into a 48k Spectrum compatibility modeThe original Spanish ZX Spectrum 128 included four additional commands in Spanish, one of which was undocumented. These can be translated as:
EDIT (to edit a line number or invoke the full screen string editor)RENUM (to renumber the program lines)DELETE (to delete program lines)WIDTH (to set the column width of the RS232 device, but undocumented as the code was broken)Unlike the LEFT$(), MID$() and RIGHT$() functions used in the ubiquitous Microsoft BASIC dialects for home computers, parts of strings in Sinclair BASIC are accessed by numeric range. For example, a$(5 TO 10) gives a substring starting with the 5th and ending with the 10th character of the variable a$. Thus, it is possible to replace the LEFT$() and RIGHT$() commands by simply omitting the left or right array position respectively; for example a$( TO 5) is equivalent to LEFT$(a$,5). Further, a$(5) alone is enough to replace MID$(a$,5,1).
Official versions
DELETE deletes BASIC program line ranges. ⇧ Shift+0 with the K cursor produces the command DELETE.FREE is a function that gives the amount of free RAM. PRINT FREE will show how much RAM is free.ON ERR is an error-handling function mostly used as ON ERR GO TO or ON ERR CONT.RESET can be used to reset the behaviour of ON ERR. It was also intended to reset peripherals.SOUND controls the AY-3-8192 sound chip.STICK is a function that gives the position of the internal joystick (Timex Sinclair 2090).Interpreters for the ZX Spectrum family
Several ZX Spectrum interpreters exist.
Compilers for the ZX Spectrum family
Several ZX Spectrum compilers exist.