| TI BASIC | |
|---|---|
 | |
| Paradigm | Imperative |
| First appeared | 1979; 46 years ago (1979) |
| Typing discipline | Static,strong |
| Platform | TI-99/4, TI-99/4A |
| License | Proprietary |
TI BASIC is anANSI-compliantinterpreter for theBASIC programming language built into the 1979 Texas Instruments TI-99/4home computer and its improved 1981 version, theTI-99/4A.
In contrast to most BASICs found on contemporarymicrocomputers, TI BASIC does not trace its history toMicrosoft BASIC, but was instead developed in-house following the emergingMinimal BASIC standard being created by ANSI andECMA. This was, in turn, based on the originalDartmouth BASIC from the 1960s. There are a number of differences, sometimes subtle, between TI BASIC and the more common MS varieties.
Minimal BASIC lacks a number of features that are commonly found on contemporary BASICs, and Texas Instruments later introduced theTI Extended BASIC cartridge that enhanced the functionality accessible to BASIC users. This included a wide variety of features found in other BASICs, as well as new system functions forsprite handling, sound, and other features of the platform.
As was common on home computers, TI BASIC was used not only for programming but also as a thinoperating system. On top of Minimal BASIC, TI added commands for text, graphics, and basic file operations like recording totape or any other file system. Due to the specifics of the TI-99 platform, TI BASIC was most notable for its extremely slow performance, roughly half that of common machines, but conversely sported high numerical accuracy.
The TI-99 was based on theTMS9900microprocessor, a16-bit design that was originally built to provide a single-chipcentral processing unit (CPU) in low-end models of theirTI-990minicomputer lineup. The TMS9900 was also suitable for use in a microcomputer, but at that time the rest of the support chips required to build a complete computer were invariably8-bit, and this included TI's wide catalog of such chips. In a minicomputer, 16-bit support systems were built up of many individual chips, but this was not suitable for a low-cost product. TI thus adopted the solution of making the machine mostly 8-bit and connecting the various support chips to this 8-bitbus, with the TMS9900 reading the bus twice to produce a 16-bit value.[1]
The TMS9900'sinstruction set architecture was based on 16-bitopcodes, meaning that programs would generally be twice as large as they would be on an 8-bit machine. In the era of expensive memory, this presented a significant cost. To address this, TI created an 8-bitvirtual machine with its own language orintermediate representation known as the "Graphic Programming Language", or GPL, that allowed programs to be written in a more compact format. The downside to this approach is that every GPL instruction had to be converted on the fly into one or more underlying TMS9900 instructions.[2] The GPL code itself was stored on the 8-bit side of the machine, further slowing its performance.[3]
For all of these reasons, the machine ran far slower than it was theoretically capable of. This was particularly noticeable in BASIC. Every instruction in the user's program had to be read from 8-bit memory, interpreted using code written in GPL, and then output back over the 8-bit bus again. As a result, TI BASIC had poor performance; on common benchmarks of the era, the TI-99 generally ran half as fast as 8-bit machines like theCommodore PET orApple II.[4] For instance, running theByte Sieve in BASIC took 3960 seconds in TI BASIC, while the same test inApplesoft BASIC on the Apple II, ostensibly a much slower machine, took 2806 seconds, about 30% faster that the TI.[5]
Unlike most BASICs of the era, TI BASIC did not provide afull-screen editor. Instead, aline editor was provided, which allowed the user to add or edit one line at a time. Explicit line numbers were used to order each statement. It used a> prompt to indicate the current new line inimmediate mode, as opposed to the more commonREADY.[6] Line numbers ranged from 1 to 32767, inclusive, and entering a line outside that range resulted in the "BAD LINE NUMBER" error.[7] Line entry was aided by theNUMBER command, available only in immediate mode, which entered ascending line numbers,[8] andRESEQUENCE, which renumbered an existing program.[9]
TI BASIC also included a number ofdebugging commands.BREAK worked something likeSTOP, stopping execution on certain lines. UnlikeSTOP, the exit to immediate mode did not occur on the line whereBREAK appeared, but on the linesBREAK referred to. For instance,BREAK 130 would cause the program to exit to immediate mode whenever it moved to line 130. This could be used, for example, by inserting a singleBREAK at the top of the program to control execution, rather than having to insert aSTOP in the middle of the code.UNBREAK turned off existing breakpoints.[10] Additionally,TRACE printed out the line number of the currently executing line in angle-brackets:<100><110> etc, andUNTRACE turned it off.[11]
The ANSI-compatiblestatements of TI BASIC areDATA, DEF, DIM, END,FOR..TO..STEP..NEXT,GOSUB,GOTO,IF..THEN..ELSE, INPUT, LET, NEXT, ON..GOSUB, ON..GOTO, OPTION BASE, PRINT,RANDOMIZE, READ,REM, RESTORE,RETURN, STOP. Most of these operate in the same fashion as their MS counterparts with two additions;RANDOMIZE restarts therandom number generator at a given "seed" value, andOPTION BASE sets the first entry in arrays to either 0 or 1, whereas MS is always zero-based. To this standard set it addedCALL,CLOSE,DISPLAY andOPEN.[12]
In keeping with the Minimal BASIC standard,[13]IF statements could only perform branches, they could not perform arbitrary statements as was common in almost every other BASIC of the era. For instance, code such as:
100IFX>5THENPRINT"IT IS LARGE"
is not valid in TI BASIC. Instead, this would have to be performed using multiple lines:
100IFX<=5THEN300200PRINT"IT IS LARGE"
This can easily lead tooff-by-one errors if the conversion is not careful about changing the sense of the Boolean comparison. TI BASIC did, however, support theELSE clause:[14]
100IFX>5THEN200ELSE300
ThePRINT statement used colons to separate items on different lines, in addition to the more common comma or semicolon. This precluded its use as a statement separator, a concept that TI BASIC did not have.[15] This means a line can have only a single statement. Due to the way BASIC interpreters work,GOTO-based loops can be sped up significantly by combining code onto a single line, which reduces the number of lines in the program and the corresponding amount of time needed to find a particular line number. This seemingly minor missing feature may result in much slower code, and adding this feature was part of TI Extended BASIC.
Extensions to the Minimal BASIC system were often not represented directly in BASIC, but were instead accessed via theCALL command and a series of named GPL-based subroutines. For instance,CALL CLEAR clears the screen, andCALL KEY returns the keycode of the currently pressed key on the keyboard. The language lackedPEEK andPOKE so there was no official way[16] to create new CALLable code within BASIC, to do this one would require the TI Editor/Assembler, the TI Mini Memory cartridge which included a smallassembler,[17] or by using Extended BASIC.
Unlike Microsoft BASICs, which usedLEFT$,MID$,RIGHT$, andINSTR for manipulating strings, TI BASIC used the ANSI-compliantSEG$ andPOS.
Subprograms are called withCALL statement (e.g.CALL CLEAR).
CHAR Definition of graphical charactersCLEAR Clears thescreenCOLOR Defines foreground- and background color for 8 charactersGCHAR Reads one character at a specified position from the screenHCHAR Writes a character to a screen position and repeats it horizontallyJOYST Returns the position of thejoystickKEY Reads from the keyboard without echo on the screenSCREEN Changes the color of the screenSOUND Creates sounds (using afrequency) and noiseVCHAR Writes a character to a screen position and repeats it vertically
TI BASIC was located in the system's internalROMs. In 1981, TI released a plug-inROM cartridge that added additional functions to the existing code, improving the language in a number of ways.[18] Known as Extended BASIC, it was a highly anticipated addition to the platform.[19]
Among the changes was the addition of the ability to have multiple statements on a line. Using multiple statements may improve performance; loops that are implemented in a single line run much faster. Additionally, statements could now span several lines. As the underlying dialect already used the colon for string separators, Extended BASIC used the double-colon for this purpose. Confusingly, as a statement with two colons was also possible in TI BASIC, for instance,PRINT"A"::"B", which would output "A", a blank line and then "B", so these statements required a space to be added in Extended BASIC,PRINT"A"::"B".[18]
Another overdue addition was thatIF statements could now perform arbitrary statements, rather than only aGOTO. In Extended BASIC one could write a simple statement likeIFX>10THENX=X-1. This also worked in theELSE clause, allowing statements likeIFA=4ANDB=6THENR=10ELSEPRINT"OOPS".[18]
Other additions include a small selection of new statements, includingACCEPT,IMAGE,LINPUT,ON BREAK,ON ERROR,ON WARNING,SUB,SUBEND andSUBEXIT. The last three statements are used forstructured programming, allowing the creation of namedsubroutines. Extended BASIC also included a number of new functions and especially CALLable routines. Among the latter was a library of sprite commands, including ones that created motion that continued automatically.[18]
When equipped with the TI Speech Synthesizer, TI Extended BASIC users could alsogenerate speech from a predefined vocabulary as easily as writing text on-screen. For example, the following line of text would cause the speech synthesizer to identify the computer:[18]
CALL SAY("HELLO I AM A #TEXAS INSTRUMENTS# T I NINETY NINE FOUR A HOME COMPUTER")Multi-word phrases aredelimited with the # symbol, as#TEXAS INSTRUMENTS# in this example. Using a word not included in the speech synthesizer's built-in vocabulary of 338 words and phrases would cause it to slowly spell out the word. TI's Terminal Emulator II cartridge providedtext-to-speech functionality.[18]