Sinclair BASIC

Template:Use dmy dates Template:Use British English Template:Short description Template:For

Sinclair BASIC is a dialect of the programming language BASIC used in the 8-bit home computers from Sinclair Research, Timex Sinclair and Amstrad. The Sinclair BASIC interpreter was written by Nine Tiles Networks Ltd.<ref name="Garfield"/>

Designed to run in only 1 KB of RAM, the system makes a number of decisions to lower memory usage. This led to one of Sinclair BASIC's most notable features, that the keywords were entered using single keystrokes; each of the possible keywords was mapped to a key on the keyboard, when pressed, the token would be placed into memory while the entire keyword was printed out on-screen. This made code entry easier whilst simplifying the parser.

The original ZX80 version supported only integer mathematics, which partially made up for some of the memory-saving design notes which had negative impact on performance. When the system was ported to the ZX81 in 1981, a full floating point implementation was added. This version was very slow, among the slowest BASICs on the market at the time, but given the limited capabilities of the machine, this was not a serious concern. The low speed was not mainly due to an inefficient interpreter though, it was an effect of the fact that 70-80% of the machine cycles were consumed by the video hardware. So the Z80 in the ZX81 clocked at 3.25 MHz was "in effect" running at well below 1 MHz from the perspective of the BASIC system.

Performance became a more serious issue with the release of the ZX Spectrum in 1982, which ran too slowly to make full use of the machine's new features. This led to an entirely new BASIC for the following Sinclair QL, as well as a number of 3rd-party BASICs for the Spectrum and its various clones. The original version continued to be modified and ported in the post-Sinclair era.

HistoryEdit

Clive Sinclair initially met with John Grant, the owner of Nine Tiles, in April 1979 to discuss a BASIC for Sinclair's new computer concept.Template:Sfn Sinclair was inspired to make a new machine after watching his son enjoy their TRS-80, but that machine's £500 price tag appeared to be a serious limit on its popularity. He wanted a new kit that would expand on their previous MK14 and feature a built-in BASIC at the target price of £79.95. To meet this price point, the machine would ship with only 1 KB of RAM and 4 KB of ROM. Grant suggested using the Forth language instead, but the budget precluded this. Grant wrote the BASIC interpreter between June and July 1979, but the code initially came in at 5 KB and he spent the next month trimming it down. It was initially an incomplete implementation of the 1978 American National Standards Institute (ANSI) Minimal BASIC standard with integer arithmetic only, termed 4K BASIC.Template:Sfn

Even before the ZX80 was introduced in February 1980, the constant downward price-pressure in the industry was allowing the already inexpensive design to be further reduced in complexity and cost. In particular, many of the separate circuits in the ZX80 were re-implemented in a single uncommitted logic array from Ferranti, which allowed the price to be reduced to only £49.95 while increasing the size of the ROM to 8 KB. This work was assigned to Steve Vickers, who joined Nine Tiles in January 1980. Whilst Grant worked on the code interfacing with hardware, Vickers used the larger space to introduce floating-point arithmetic and a suite of trig functions, which were expected of any BASIC from that era, producing 8K BASIC.Template:Sfn The initial version did not support the ZX Printer and had a bug in its square root function. Nine Tiles provided a new version to address these, but Sinclair was slow to include the new version in the ROMs. The new ROMs were eventually offered to owners of the earlier ZX80 as well.<ref name=8Kupgrade>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

When Sinclair lost the contest to build the BBC Computer, he moved ahead with plans to produce a low-cost colour-capable machine that emerged as the ZX Spectrum of April 1982. ROM space would once again be increased, this time to 16 KB. In keeping with his philosophy of making systems for the lowest possible expenditure, Sinclair wanted the absolute minimum changes to the existing 8K BASIC. Although Nine Tiles felt that something much better would be needed for the new machine, the schedule would not allow it, and yet another expansion of the original code was produced. Due to the RAM also being increased, to 48 KB, this version was known as 48K BASIC and eventually 48 BASIC with the introduction of the ZX Spectrum 128 at which time the 16 KB Spectrum was no longer sold and most existing ones in use had been upgraded to 48 KB.<ref name="worldofspectrum.org" /><ref name=":0" /> The new version was available near the end of 1981, but it was "depressingly slow" and "snail like". Additionally, as no prototypes were available until the end of the year, it lacked support for the new line of peripherals Sinclair was planning.<ref name=reg>Template:Cite magazine</ref>

In February 1982, Nine Tiles began to have disagreements with Sinclair over owed royalties for the various manuals that Nine Tiles had produced. Around the same time, Vickers and his Sinclair counterpart, Richard Altwasser, left their respective companies to start the Jupiter Ace project.Template:Sfn When the Spectrum was launched the ROM was still not complete, and although Nine Tiles continued working on it until April 1982, by that point 75,000 Spectrums had already been sold and the project was cancelled. The missing functionality was later added by additional code in the ZX Interface 1. After Nine Tiles and Sinclair went their own ways, several new versions of 48 BASIC were created.

In 1983, as part of introducing the Spectrum to the US market as the TS2068, Timex modified it as T/S 2000 BASIC. The new version was incapable of running many Spectrum programs due to the memory location of machine's functions moving. A similar, but somewhat more compatible version, was introduced as part of the Spanish Spectrum 128 of 1985, 128 BASIC.<ref name=":0" />

Amstrad purchased Sinclair Research in 1986. As Sinclair had never owned the copyright to the language, Amstrad had to arrange a new license with Nine Tiles. Several other versions also appeared in this period as various extensions and clones of the Spectrum were introduced. These included +3 BASIC, BASIC64 and Timex Extended Basic.<ref name=":0" /><ref name="worldofspectrum.org" />

As of 2015, interpreters exist for modern operating systems,<ref>Template:Citation</ref> and older systems,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> that allow Sinclair Basic to be used easily.

DescriptionEdit

Program editingEdit

Like most home-computer BASICs, Sinclair BASIC is anchored around its line editor. When the machine is booted, it runs BASIC and displays an inverse video "K" at the bottom of the screen to indicate the entry point. When a line is entered and the Template:Keypress key is pressed, it either runs immediately if it does not have a line number prefix, or clears the screen and performs the equivalent of a <syntaxhighlight lang="text" class="" style="" inline="1">LIST</syntaxhighlight> command, placing a ">" cursor after the line number in the most recently entered line.

In contrast to most machines of the era, the editor does not allow freeform editing at any point on the screen. Instead, when the user presses Template:Key press, the current line of code is copied back to the bottom of the screen. The user can move horizontally through this line using the cursor keys and commits their changes by pressing Template:Key press again. In contrast, on machines like the Commodore 64 or Atari 8-bit computers, the up and down keys can be used to move among the lines in the program and edit them in-place.

The most notable feature of the editor is that keywords are entered using single keystrokes. For instance, on the ZX81, the Template:Key press key on the keyboard would cause the entire keyword <syntaxhighlight lang="text" class="" style="" inline="1">PRINT</syntaxhighlight> to be entered into the currently editing line. Once a keyword has been entered, the cursor changes to an "L" to indicate what follows will be interpreted as normal text. For instance, pressing Template:Key press again at this point would enter a single letter "P".

Keys generally had two separate keywords assigned to themTemplate:Snd one above it and one below. Pressing the key in "K" mode would enter the keyword above the key, like <syntaxhighlight lang="text" class="" style="" inline="1">PRINT</syntaxhighlight> for Template:Key. If the system was in "L" mode, one could return to "K" by pressing the shift key Template:Snd the systems did not initially support lowercase text, so the shift was not otherwise needed. The keywords below the keys required a second keystroke, Template:Key press, which put the editor into "function mode", changing the cursor to an "F". Entering common code often resulted in a significant number of keystrokes.

The system has the advantage of representing all multi-character keywords as a single character in memory, which was a significant savings in the early machines that shipped with only 1 KB of RAM. This single-character representation included multi-character items like <syntaxhighlight lang="text" class="" style="" inline="1"><></syntaxhighlight>. This has the added advantages of simplifying the runtime, as it can immediately determine whether a character in the source code is a keyword or text, and also means that keywords are never entered directly, meaning that one can, for instance, have a variable named "PRINT", as the system can determine that it is not the same as the keyword.

As the systems evolved and added new keywords, the entry system became increasingly difficult to use. 48 BASIC in the Spectrum required every key to host up to four keywords. Entering keywords was a time-consuming process of looking over the relatively small type on the keyboard for the appropriate key, and then correctly entering the multiple keystrokes needed to enter it properly. For instance, entering <syntaxhighlight lang="text" class="" style="" inline="1">BEEP</syntaxhighlight> required one to type Template:Keypress to access extended mode (later models include a separate Template:Keypress key), keeping Template:Keypress held down, and then and pressing Template:Keypress. To improve the complex entry on the Spectrum, the keywords were colour-coded to indicate the required mode:Template:Sfn

Template:Font color: key only
Template:Font color on the key itself: Template:Keypress plus the key
Template:Font color above the key: Template:Keypress followed by the key
Template:Font color below the key: Template:Keypress followed by Template:Keypress plus the key

This concept had run its course, and later machines running 128 BASIC (ZX Spectrum 128, +2, +3, +2A, and +2B) featured a more traditional editor where the user typed-in the keyword as individual characters, similar to other home computers of the era. This required a new tokenizer to convert the line into a similar internal format.

The resulting in-memory storage of the program was otherwise similar to Microsoft BASIC, in that only the keywords are presented as tokens, while non-keywordsTemplate:Snd like string and numeric constants and variable namesTemplate:Snd are left in their original typed-in format. However, that typed-in format was not ASCII, but an internal character code that contains both printable characters and the keyword tokens. Although portions of the table, the capital letters A to Z, for instance, are in the same order as in ASCII, their characters correspond to different numeric values, i.e. their code points' offset from zero is different from ASCII's offset of 65. Other characters, like punctuation, may have been moved about even more. The ZX Spectrum character set is the most prominent example of such a character code. Related computers running Sinclair BASIC used similar variants, e.g. the ZX80 or ZX81 character sets. All of these different but related character sets included Sinclair BASIC tokens.

Data typesEdit

One uncommon feature of Sinclair BASIC is the way it stores variables in memory. Typically, interpreters use a fixed-size entry to hold data, making it easy to scan the variable table. Due to the extremely limited memory of the ZX series, any wasted space had to be avoided, and this led to the use of a variable-length format. The data types included numbers stored in a 5-byte values, strings with a length and then the characters, and arrays of both of those types. The data was stored in the table itself, which contrasts with most BASICs of the era, where strings and array entries were stored in a separate heap.

The first byte for a variable entry always held the type in the first three bits, and the first character of the name in the next five bits. As was the case in most microcomputer dialects, A, A$, A() and A$() were all different variables and could store different values. Most variables could only have a single-character name; the exception are numeric variables (not arrays), where an alternate format held the first character of the name in those same five bits, but was then followed by additional characters ending with one with its high-bit set. Long variable names were whitespace-independent, and case-insensitive in later versions, so <syntaxhighlight lang="basic" inline>LET Number Of Apples = 5</syntaxhighlight> is the same as <syntaxhighlight lang="basic" inline>LET numberofapples = 5</syntaxhighlight> referred to the same variable.

The downside to this approach is that scanning the table to look up the value of a variable reference is more complex. In addition to testing whether the name matches using the subset of the first byte, if the entry is not the one that is being looked for, the type has to be read from the upper three bits and then the next location of a variable in storage calculated using the type. For instance, if the program encounters the variable "A" and the table starts with the entry for "B$", it fails to match A with B, then reads the type to see it is a string, and then has to read the following length byte and skip forward by that amount of bytes to find the next entry in the table. To make this somewhat easier, arrays also stored a two-byte length, so the entire structure could be skipped over more easily.

A unique feature was the "short float", or integer type. Any numeric variable could store either type, the storage itself did not change and used 5 bytes in either case. Integers were indicated by setting the exponent byte to zero, while floating-point values were stored with an excess-128 format exponent. This meant that it could not store zero as a float and lost one possible exponent magnitude. It also did not use any less memory, as the values were still 5-byte in memory. The advantage to this format is performance; the math library included tests to look for the zero exponent, and if it was seen, it would not attempt to perform various operations on the remaining 3 bytes under certain conditions.

Keyword detailsEdit

The ZX81 8K BASIC used the shorter forms GOTO, GOSUB, CONT and RAND, whereas the Spectrum 48 BASIC used the longer forms GO TO, GO SUB, CONTINUE and RANDOMIZE. The ZX80 4K BASIC also used these longer forms but 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 Template:Nowrap 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 <syntaxhighlight lang="basic" inline>LET</syntaxhighlight> (i.e., <syntaxhighlight lang="basic" inline>LET A=1</syntaxhighlight> not only <syntaxhighlight lang="basic" inline>A=1</syntaxhighlight>). 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

128 BASIC, present on ZX Spectrum 128, +2, +3, +2A, and +2B, stored keywords internally in one-byte code points, but used a conventional letter-by-letter BASIC input system. It also introduced two new commands:

PLAY, which operated the 128k models' General Instrument AY-3-8910 music chip
SPECTRUM, which switched the 128k Spectrum into a 48k Spectrum compatibility mode

The original Spanish ZX Spectrum 128 included four additional BASIC editor commands in Spanish,<ref name="Disassembly"/><ref>Template:Cite book</ref> one of which was undocumented:

EDITAR (to edit a line number or invoke the full screen string editor)
NUMERO (to renumber the program lines)
BORRAR (to delete program lines)
ANCHO (to set the column width of the RS-232 device, but undocumented as the code was broken)

Unlike the LEFT$(), MID$() and RIGHT$() functions used in the ubiquitous Microsoft BASIC dialects for home computers, parts of strings in Sinclair BASIC are accessed by numeric range. For example, Template:Nowrap gives a substring starting with the 5th and ending with the 10th character of the variable a$. Thus, it is possible to replace the LEFT$() and RIGHT$() commands by simply omitting the left or right array position respectively; for example Template:Nowrap is equivalent to LEFT$(A$,5). Further, a$(5) alone is enough to replace MID$(A$,5,1).

SyntaxEdit

KeywordsEdit

On the 16K/48K ZX Spectrum (48 BASIC), there are 88 keywords in Sinclair BASIC, denoting commands (of which there are 50), functions and logical operators (31), and other keywords (16, including 9 which are also commands or functions):

Keyword	Parameters<ref group="note">Optional parameters are enclosed in [square brackets]</ref>	Entered using<ref group="note">These assume the computer is in Template:Font color (keyword) mode, which it normally is at the start of a line when entering BASIC. On the Spectrum 16K and 48K, Extended Mode is entered by pressing Template:Keypress and Template:Keypress simultaneously rather than the Template:Keypress key that is present on the Spectrum+ and later models.</ref>	Type	Summary
`ABS`	`number`	Template:Keypress then Template:Keypress	Function	Returns the absolute value of `number`Template:Sfn
`ACS`	`number`	Template:Keypress then Template:Keypress	Function	Returns the arccosine of `number`Template:Sfn
`AND`		Template:Keypress	Logical operator	Returns true if both conditions on either side of the `AND` keyword are true, else returns false<ref group="note" name="logical"/>Template:Sfn
`ASN`	`number`	Template:Keypress then Template:Keypress	Function	Returns the arcsine of `number`Template:Sfn
`AT`	`line, column;`	Template:Keypress	Other	Used in a `PRINT` statement to print at the line and column specified;Template:Sfn for example, `PRINT AT 5,10;"*"` puts a star in column 10 of line 5.
`ATN`	`number`	Template:Keypress then Template:Keypress	Function	Returns the arctangent of `number`Template:Sfn
`ATTR`	`(line, column)`	Template:Keypress then Template:Keypress	Function	Returns a byte containing information on the colours of the text cell on the screen, corresponding to the specified `line` and `column`; note that, unlike most Sinclair BASIC keywords, the parentheses are required; the first three bits indicate the ink (foreground) colour, the fourth, fifth and sixth bits the paper (background) colour, the seventh bit whether the colours are bright or not, and the eight, whether they are flashingTemplate:Sfn
`BEEP`	`duration, pitch`	Template:Keypress then Template:Keypress	Command	Produces sound from the computer's speaker; `duration` is in seconds, pitch is in semitones above (positive value) or below (negative value) middle C Template:Sfn
`BIN`	`number`	Template:Keypress then Template:Keypress	Other	Indicates `number` is in binary notation Template:Sfn
`BORDER`	`number`	Template:Keypress	Command	Sets the border of the screen to the colour specified by the `number`<ref group="note" name="colournumbers"/>Template:Sfn
`BRIGHT`	`number`	Template:Keypress then Template:Keypress	Command/other	Makes all following colours brighter if `number` is 1, or its normal shade if 0<ref group="note" name="colours"/>Template:Sfn
`CAT`	`number`	Template:Keypress then Template:Keypress	Command	Displays contents of ZX Microdrive specified by `number`<ref group="note" name="microdrivecommands"/>Template:Sfn
`CHR$`	`number`	Template:Keypress then Template:Keypress	Function	Returns the character corresponding to the decimal `number` in the computer's character set Template:Sfn
`CIRCLE`	`x, y, r`	Template:Keypress then Template:Keypress	Command	Draws a circle with its centre at coordinates (`x`,`y`) and radius `r`Template:Sfn
`CLEAR`	`address`	Template:Keypress	Command	Clears the screen,Template:Sfn all variables and the `GO SUB` stack,<ref>{{#invoke:citation/CS1\|citation	CitationClass=web }}</ref> and optionally sets the maximum RAM address to be used by BASICTemplate:Sfn
`CLOSE #`	`number`	Template:Keypress then Template:Keypress	Command	Closes the specified stream number for access<ref group="note" name="microdrivecommands"/>
`CLS`		Template:Keypress	Command	Clears all text and graphics from the screenTemplate:Sfn
`CODE`	`string`	Template:Keypress then Template:Keypress	Function/other	Returns the number corresponding to the first character in `string` in the computer's character set;Template:Sfn also used to save arbitrary chunks memory to tape, disk, etc. and load them back in – see `LOAD`, `SAVE` and `VERIFY` for details
`CONTINUE`		Template:Keypress	Command	Restarts a program after it has stopped due to an error or the user pressing the Template:Keypress or Template:Keypress keysTemplate:Sfn
`COPY`		Template:Keypress	Command	Sends the currently displayed screen to the printerTemplate:Sfn
`COS`	`number`	Template:Keypress then Template:Keypress	Function	Returns the cosine of `number`Template:Sfn
`DATA`	`comma-separated values`	Template:Keypress then Template:Keypress	Command/other	Provides numbers and/or strings to use with the `READ` commandTemplate:Sfn and allows saving the contents of an array to tape when used with the `SAVE` commandTemplate:Sfn (as `SAVE filename DATA array name()`)
`DEF FN`	`name(variable) = operation`	Template:Keypress then Template:Keypress	Command	Defines a custom function that can be used with the `FN` command;function definitions must be of the form `f(x)=operations`, for example `f(x)=x*2` and the function name may not consist of more than one letter, plus a $-symbol if the function returns a stringTemplate:Sfn
`DIM`	`variable(dimensions)`	Template:Keypress	Command	Declares an array with the specified `dimensions`, which may be multi-dimensional (for example, `DIM a(10,10)`; if used with strings, the last dimension indicates the length of each of the strings (thus, `DIM A$(2,5)` is an array of two strings each of five characters long, and `DIM B$(5)` is one string of five characters)Template:Sfn
`DRAW`	`x, y [, r]`	Template:Keypress	Command	Draws a line in the current `INK` colour to coordinates (`x`,`y`) from the coordinates used by the previous `PLOT` or `DRAW` command; if the optional `r` is supplied, it indicates the radius of the circle segment to be drawn, in radians Template:Sfn
`ERASE`	`drive;"filename"`	Template:Keypress then Template:Keypress	Command	Deletes the specified file from a ZX Microdrive<ref group="note" name="microdrivecommands"/>Template:Sfn
`EXP`	`number`	Template:Keypress then Template:Keypress	Function	Returns e to the power `number`Template:Sfn
`FLASH`	`number`	Template:Keypress then Template:Keypress	Command/other	Makes all following text alternate its foreground (`INK`) and background (`PAPER`) colours<ref group="note" name="colours"/>
`FN`	`function(value)`	Template:Keypress then Template:Keypress	Function	Calls the `function` defined earlier in the program using `DEF FN`Template:Sfn
`FORMAT`	`drive;"name"`	Template:Keypress then Template:Keypress	Command	Formats the cartridge in the indicated Microdrive and assigns it the identifier `name`<ref group="note" name="microdrivecommands"/>Template:Sfn
`FOR`	`variable = start TO end`	Template:Keypress	Command	Starts a `FOR`-`NEXT` loop;Template:Sfn the variable name may only be one character longTemplate:Sfn
`GO SUB`	`number`	Template:Keypress	Command	Makes the program jump to the BASIC line specified by `number`; when the program encounters the command `RETURN`, it will jump back to the statement after the `GO SUB`Template:Sfn
`GO TO`	`number`	Template:Keypress	Command	Makes the program jump to the BASIC line specified by `number`
`IF`	`condition THEN`	Template:Keypress	Command	Evaluates the `condition`, and if true, executes the statement that follows the keyword `THEN` that must come after the condition,Template:Sfn for example <syntaxhighlight lang="basic" class="" style="" inline="1">IF A=1 THEN LET B=2</syntaxhighlight><ref group="note" name="if-else"/>
`IN`	`address`	Template:Keypress then Template:Keypress	Function	Returns a byte read from the hardware input/output port corresponding to the `address`Template:Sfn
`INK`	`number`	Template:Keypress then Template:Keypress	Command/other	Sets the foreground colour for text and graphics<ref group="note" name="colournumbers"/><ref group="note" name="colours"/>Template:Sfn
`INKEY$`		Template:Keypress then Template:Keypress	Function	Returns a string representing the key being pressed on the keyboard at the moment the function is called, or an empty string if none is,Template:Sfn but does not wait for a keypress
`INPUT`	`[prompt,] variable`	Template:Keypress	Command	Halts program execution until the user types in something on the keyboard and presses the `Enter` key, then stores the entered value in the specified `variable`; if the optional `prompt` is supplied, this will be shown on the screenTemplate:Sfn
`INT`	`number`	Template:Keypress then Template:Keypress	Function	Returns the integer value of `number`, rounding down to the nearest whole numberTemplate:Sfn (thus, `INT -1.1` returns −2, not −1)
`INVERSE`	`number`	Template:Keypress then Template:Keypress	Command/other	Reverses the colours on all following text if `number` is 1, so that it uses the current ink colour for the background and the current paper colour for the text, or sets them back to normal if `number` is 0<ref group="note" name="colours"/>Template:Sfn
`LEN`	`string`	Template:Keypress then Template:Keypress	Function	Returns the number of characters (bytes) in `string`Template:Sfn
`LET`	`variable=value`	Template:Keypress	Command	Assigns `value` to the named variableTemplate:Sfn
`LINE`		Template:Keypress then Template:Keypress	Other	When used in an `INPUT` statement before a string variable, will not put quotation marks ("") around its prompt,Template:Sfn for example <syntaxhighlight lang="basic" class="" style="" inline="1">INPUT "Name: "; LINE n$</syntaxhighlight> When used in a `SAVE` statement so that when the BASIC program being saved is loaded again, it starts automatically at the line number indicatedTemplate:Sfn
`LIST`	`[number]`	Template:Keypress	Command	Outputs the current BASIC program to the screen; if the optional `number` is provided, it omits all lines with a lower numberTemplate:Sfn
`LLIST`	`[number]`	Template:Keypress then Template:Keypress	Command	As `LIST` except the listing is output to the printerTemplate:Sfn
`LN`	`number`	Template:Keypress then Template:Keypress	Function	Returns the natural logarithm of `number`Template:Sfn
`LOAD`	`"[filename]" [CODE [address[, length]]\| DATA variable()]`	Template:Keypress	Command	Loads a program or data into RAM from tape, ZX Microdrive, disk, etc., deleting any existing BASIC program and variables;Template:Sfn if an empty string (`""`) is provided, this loads the first program found, else it will search the tape for the program named in the string; if the optional `CODE` is provided, will load the program into memory at the address it had when it was saved, or at the specified `address` (`length` is intended as a safety, to try and load the right program in case there are multiple on the tape with the right name but of different lengths);Template:Sfn if the optional `DATA variable()` is provided, will load the data from the tape into the array named `variable()`Template:Sfn
`LPRINT`	`text`	Template:Keypress then Template:Keypress	Command	As `PRINT` except output is sent to the printerTemplate:Sfn
`MERGE`	`"[filename]"`	Template:Keypress then Template:Keypress	Command	As `LOAD`, except it does not delete the current program and variables; if a line number exists in both, that of the newly loaded program overwrites the existing one. Using `MERGE` prevents a program saved using `LINE` from auto-running once loadedTemplate:Sfn
`MOVE`	`stream1 TO stream2`	Template:Keypress then Template:Keypress	Command	Moves data from one stream (keyboard, screen, file, printer, network, etc.) to another<ref group="note" name="microdrivecommands"/>Template:Sfn
`NEW`		Template:Keypress	Command	Erases the current BASIC program and all variablesTemplate:Sfn
`NEXT`	`variable`	Template:Keypress	Command	Closes a `FOR`-`NEXT` loop; the variable must match that of the corresponding `FOR` commandTemplate:Sfn – "empty" `NEXT`s to refer to the immediately preceding `FOR` in the program are not allowed
`NOT`	`condition`	Template:Keypress	Logical operator	Returns true if the `condition` is false, else returns false<ref group="note" name="logical"/>Template:Sfn
`OPEN #`	`stream`	Template:Keypress then Template:Keypress	Command	Opens a stream for reading from and/or writing to<ref group="note" name="microdrivecommands"/>Template:Sfn
`OR`		Template:Keypress	Logical operator	Returns true if either of the conditions on either side of the `OR` keyword are true, else returns false<ref group="note" name="logical"/>Template:Sfn
`OUT`	`address, value`	Template:Keypress then Template:Keypress	Command	Sends the `value` (a byte) to the hardware input/output port corresponding to the `address`.Template:Sfn
`OVER`	`number`	Template:Keypress then Template:Keypress	Command/other	Will make following text overprint with an XOR operation what is already on the screen if `number` is 1, instead of erasing it, or erase it if `number` is 0<ref group="note" name="colours"/>Template:Sfn
`PAPER`	`number`	Template:Keypress then Template:Keypress	Command/other	Sets the background colour for text and graphics<ref group="note" name="colournumbers"/><ref group="note" name="colours"/>Template:Sfn
`PAUSE`	`delay`	Template:Keypress	Command	Halts program execution for the specified delay, in <math>\tfrac {1}{50}</math> of a second in Europe or <math>\tfrac {1}{60}</math> in North AmericaTemplate:Sfn (thus, `PAUSE 50` halts for one second in Europe)
`PEEK`	`address`	Template:Keypress then Template:Keypress	Function	Returns a byte representing the contents of the memory location pointed to by `address`Template:Sfn
`PI`		Template:Keypress then Template:Keypress	Function	Returns the value of pi Template:Sfn
`PLOT`	`x, y`	Template:Keypress	Command	Draws a pixel in the current `INK` colour on the screen at the coordinates (`x`,`y`)Template:Sfn
`POINT`	`(x,y)`	Template:Keypress then Template:Keypress	Function	Returns 1 if the pixel pointed at graphical coordinates (`x`,`y`) is currently in the ink (foreground) colour, else returns 0Template:Sfn
`POKE`	`address, value`	Template:Keypress	Command	Sets the contents of `address` in RAM to `value`Template:Sfn
`PRINT`	`[AT x,y;] text`	Template:Keypress	Command	Prints `text` (which must be one or more strings or numbers separated with semicolons) to the screen.Template:Sfn If used with #0 or #1, it prints in the bottom two (input) lines of the screen; if used with `AT`, it prints at the specified text coordinates; otherwise, it prints either immediately following the output of any previous `PRINT` statement (if the previous statement ended in a semicolon), or in the first column of the line below the previous `PRINT` output,Template:Sfn defaulting to 0,0.
`RANDOMIZE`	`[number]`	Template:Keypress	Command	Initializes the random number generator; if used without a `number` (or with 0), it does this based on the computer's internal clock, else it uses the `number` supplied, which must be in the range [1,65535]Template:Sfn
`READ`	`variable`	Template:Keypress then Template:Keypress	Command	Takes a value from a `DATA` statement and stores it in the named `variable`: the first time `READ` is used, it gets the first value after the first `DATA`, the second time it gets the next one, and so onTemplate:Sfn
`REM`	text	Template:Keypress	Command	Begins a comment in the source code, meaning that everything after the `REM` statement is ignored, until the end of the lineTemplate:Sfn – note this includes everything after a colon, which normally begins a new segment: <syntaxhighlight lang="basic" class="" style="" inline="1">10 REM Nothing to see here: PRINT "Unprintable"</syntaxhighlight> will not produce any output, for example.
`RESTORE`	`[number]`	Template:Keypress then Template:Keypress	Command	Resets where `READ` commands look for values in `DATA` statements: if used without a number, the next `READ` will use the first `DATA` in the program, with a number it will use the first `DATA` on or after the line whose number is indicatedTemplate:Sfn
`RETURN`		Template:Keypress	Command	Returns execution to the first statement following the last `GO SUB` command that was executedTemplate:Sfn
`RND`		Template:Keypress then Template:Keypress	Function	Returns a pseudo-random number with eight significant figures in the range [0,1)Template:Sfn
`RUN`	`[number]`	Template:Keypress	Command	Starts the current BASIC program, from its first line if no `number` is specified, else from the line with that number (or the first one after, if it does not exist)Template:Sfn
`SAVE`	`"filename" [DATA variable() Template:Pipe LINE number]`	Template:Keypress	Command	Saves the current BASIC program to tape or other storage device, with the `filename` specified; if the optional `LINE` followed by a line number is used, then the program will start automatically at the indicated line number when it is `LOAD`ed back in; with the optional `DATA`, the command saves the contents of the array named by the variable instead of the current BASIC programTemplate:Sfn
`SCREEN$`	`[(line, column)]`	Template:Keypress then Template:Keypress+Template:Keypress	Function/other	As a function, identifies the character at the specified line and column on the screen.Template:Sfn Used after the filename in a `LOAD` or `SAVE` command, indicates that the contents of the display memory should be loaded or saved; this essentially makes it a shortcut for `CODE 16384,6912`<ref group=note>The Spectrum’s display memory starts at address 16384 and is 6912 bytes long.</ref> but does not work with `VERIFY` because the contents of the display memory will be different by the time that command reads back the saved data;Template:Sfn
`SGN`	`number`	Template:Keypress then Template:Keypress	Function	Returns 1 if `number` is positive, 0 if it is 0, and −1 if it is negativeTemplate:Sfn
`SIN`	`number`	Template:Keypress then Template:Keypress	Function	Returns the sine of `number`Template:Sfn
`STEP`	`number`	Template:Keypress	Other	Indicates the interval used by a `FOR` statement,Template:Sfn for example <syntaxhighlight lang="basic" class="" style="" inline="1">FOR n=2 TO 6 STEP 2</syntaxhighlight> will skip `n=3` and `n=5` in the loop
`STOP`		Template:Keypress	Command	Ends execution of the current program, exiting to the BASIC editor; can also be given when the computer is waiting for input using the `INPUT` command;Template:Sfn once the program is stopped, it can be resumed with `CONTINUE`
`SQR`	`number`	Template:Keypress then Template:Keypress	Function	Returns the square root of `number`Template:Sfn
`STR$`	`number`	Template:Keypress then Template:Keypress	Function	Converts a number to string.
`TAB`	`column`	Template:Keypress then Template:Keypress	Other	In a `PRINT` statement, makes sure that the text to be output begins in the column specified, wrapping to the next line as necessary, but never more than one lineTemplate:Sfn
`TAN`	`number`	Template:Keypress then Template:Keypress	Function	Returns the tangent of `number`Template:Sfn
`THEN`	`statement`	Template:Keypress	Other	Follows the condition in an `IF` statement to indicate what should happen when the condition evaluates to true<ref group="note" name="if-else"/>Template:Sfn
`TO`		Template:Keypress	Other	Indicates a range from the number to the left of `TO` to the number of the right of it, inclusive;Template:Sfn when used with `FOR` both numbers must be supplied, while if used to slice strings, either may be left off to indicate the start or end of the string
`USR`	`string or address`	Template:Keypress then Template:Keypress	Function	When called with a single-character string, this returns the memory address at which the glyph for the user-defined graphic character corresponding to that character is defined.Template:Sfn If called with an address, it starts machine code execution at that address (thus making it one of the few Sinclair BASIC functions to have a Side effect) and returns the contents of the Z80’s BC register pair.Template:Sfn
`VAL`	`string`	Template:Keypress then Template:Keypress	Function	Evaluates the `string` as a number and returns the result;Template:Sfn this can perform calculations: `VAL "1+2"` returns 3, for example, and also evaluates variables and even other `VAL` statements: <syntaxhighlight lang="basic" class="" style="" inline="1">LET A=1: VAL "A+VAL ""2"""</syntaxhighlight><ref group="note">A string inside a string must have its quotes doubled in Sinclair BASIC.</ref> also returns 3
`VAL$`	`string`	Template:Keypress then Template:Keypress	Function	Similar to `VAL` but evaluates the string as a stringTemplate:Sfn
`VERIFY`	`"[filename]"`	Template:Keypress then Template:Keypress	Command	Reads a program or data from tape or other storage, much like `LOAD`, but instead of loading it into memory, compares it with the program or data that is already in memory. This is intended to be used immediately after a `SAVE` command, to make sure the program or data has been saved without corruption.Template:Sfn

Template:Multiple image

Official versionsEdit

4K BASICEdit

4K BASIC for ZX80<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> (so named for residing in 4 KiB read-only memory (ROM)), was developed by John Grant of Nine Tiles for the ZX80. It has integer-only arithmetic.

System Commands: NEW RUN LIST LOAD SAVE
Control Statements: GOTO IF THEN GOSUB STOP RETURN FOR TO NEXT CONTINUE
Input/Output Statements: PRINT INPUT
Assignment Statement: LET
Other Statements: CLEAR CLS DIM REM RANDOMIZE POKE
Functions: ABS CHR$ CODEPEEK RND STR$ TL$ USR

8K BASICEdit

8K BASIC is the ZX81 BASIC (also available as an upgrade for the ZX80<ref name="8Kupgrade" />), updated with floating-point arithmetic by Steve Vickers, so named for residing in 8 KiB ROM.

Statements: PRINT RAND LET CLEAR RUN LIST GOTO CONT INPUT NEW REM PRINT STOP BREAK IF STOP FOR NEXT TO STEP SLOW FAST GOSUB RETURN SAVE LOAD CLS SCROLL PLOT UNPLOT PAUSE LPRINT LLIST COPY DIM POKE NEW
Functions: ABS SGN SIN COS TAN ASN ACS ATN LN EXP SQR INT PI RND FUNCTION LEN VALSTR$ NOT CODE CHR$ INKEY$ AT TAB INKEY$ PEEK USR

48 BASICEdit

48 BASIC is the BASIC for the original 16/48 KB RAM ZX Spectrum (and clones), with colour and more peripherals added by Steve Vickers and John Grant. It resides in 16 KB ROM and began to be called 48 BASIC with the introduction of the ZX Spectrum 128 at which time the 16 KB Spectrum was no longer sold and most existing ones in use had been upgraded to 48 KB.<ref name="worldofspectrum.org">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

128 BASICEdit

128 BASIC is the BASIC for the ZX Spectrum 128.<ref name=":0">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It offers extra commands and uses letter-by-letter input.

New commands: LOAD ! SAVE ! MERGE ! ERASE ! PLAY SPECTRUM

+3 BASICEdit

+3 BASIC is the BASIC with disk support for the ZX Spectrum +3 and +2A.<ref name="worldofspectrum.org" />

New commands: FORMAT COPY

T/S 2000 BASICEdit

T/S 2000 BASIC is used on the Spectrum-compatible Timex Sinclair 2068 (T/S 2068) and adds the following six new keywords:

DELETE deletes BASIC program line ranges.
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).

BASIC64Edit

BASIC64 by Timex of Portugal, is a software extension<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> to allow better Basic programming with the 512×192 and dual display areas graphic modes available only on Timex Sinclair computers. This extension adds commands and does a complete memory remap to avoid the system overwriting the extended screen memory area. Two versions exist due to different memory maps – a version for TC 2048 and a version for T/S 2068 and TC 2068.

PRINT # prints to a specific output channel.
LIST # lists the program to a specific output channel.
CLS* clears both display areas.
INK* sets ink colour for both display areas
PAPER* sets paper colour both display areas
SCREEN$ selects the high / normal resolution modes.
PLOT* plots a pixel and updates the drawing position.
LINE draws a line from the previous PLOT position, supporting arc drawing
CIRCLE* draws a circle or oval, depending on screen mode.

Timex Extended BasicEdit

Timex Extended Basic by Timex of Portugal is used on the Timex Computer 3256, adding TEC – Timex Extended Commands commands supporting the AY-3-8912 sound chip, RS-232 network and the 512x192 pixel high resolution graphic mode.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

RAM drive commands: LOAD! SAVE! CAT! MERGE! ERASE! CLEAR!
RS-232 commands: FORMAT! LPRINT LLIST
AY-3-8912 commands: BEEP!
512 x 192 resolution commands: SCREEN$ DRAW! PLOT! CIRCLE!

Other versions, extensions, derivatives and successorsEdit

Interpreters for the ZX Spectrum familyEdit

Several ZX Spectrum interpreters exist.<ref name="SpectrumClassic">{{#invoke:citation/CS1|citation |CitationClass=web }} </ref>

Beta BASIC by Dr. Andy Wright, was originally a BASIC extension, but became a full interpreter.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

YS MegaBasic by Mike Leaman.<ref name="SpectrumClassic"/><ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

ZebraOS by Zebra Systems in New York, a cartridge version of T/S 2000 BASIC that used the 512×192 screen mode.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

Sea Change ROM by Steve Vickers and Ian Logan, modified by Geoff Wearmouth, a replacement ROM with an enhanced Sinclair BASIC.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

Gosh Wonderful by Geoff Wearmouth, a replacement ROM that fixes bugs and adds a tokenizer, stream lister, delete and renumber commands.<ref name="SpectrumClassic"/><ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

OpenSE BASIC (formerly SE BASIC) by Andrew Owen, a replacement ROM with bug fixes and many enhancements including ULAplus<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref> support, published as open source in 2011<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>