Applesoft BASIC

Applesoft BASIC
Original author(s) Marc McDonald and Ric Weiland
Initial release 1977 (1977)
Stable release Applesoft II / 1978 (1978)
Operating system Apple II series
Type Microsoft BASIC

Applesoft BASIC is a dialect of Microsoft BASIC, developed by Marc McDonald and Ric Weiland, supplied with the Apple II series of computers. It supersedes Integer BASIC and is the BASIC in ROM in all Apple II series computers after the original Apple II model. It is also referred to as FP BASIC (from "floating point") because of the Disk Operating System (DOS) command used to invoke it, instead of INT for Integer BASIC. Applesoft BASIC was supplied by Microsoft and its name is derived from the names of both Apple and Microsoft. Apple employees, including Randy Wigginton, adapted Microsoft's interpreter for the Apple II and added several features. The first version of Applesoft was released in 1977 only on cassette tape and lacked proper support for high-resolution graphics. Applesoft II, which was made available on cassette and disk and in the ROM of the Apple II Plus and subsequent models, was released in 1978. It is this latter version, which has some syntax differences from the first as well as support for the Apple II high-resolution graphics modes, that most people mean by the term "Applesoft."

Background

When Steve Wozniak wrote Integer BASIC for the Apple II, he did not implement support for floating point math because he was primarily interested in writing games, a task for which integers alone were sufficient.[1] In 1976, Microsoft had developed Microsoft BASIC, a BASIC interpreter for the MOS Technology 6502, but at the time there was no production computer that used it. Upon learning that Apple had a 6502 machine, Microsoft asked if the company were interested in licensing BASIC, but Steve Jobs replied that Apple already had one. The Apple II was unveiled to the public at the West Coast Computer Faire in April 1977 and became available for sale in June. One of the most common customer complaints about the computer was BASIC's lack of floating-point capability. Integer BASIC is limited to whole numbers between −32768 and 32767 and caused problems for users attempting to write business applications with it. As Wozniak—the only person who understood Integer BASIC well enough to add floating point features—was busy with the Disk II drive and controller and with Apple DOS, Apple turned to Microsoft.

Apple reportedly obtained an eight-year license for Applesoft BASIC from Microsoft for a flat fee of $31,000, renewing it in 1985 through an arrangement that gave Microsoft the rights and source code for Apple's Macintosh version of BASIC.[2] Applesoft was designed to be backwards-compatible with Integer BASIC and uses the core of Microsoft's 6502 BASIC implementation, which includes using the GET command for detecting key presses and not requiring any spaces on program lines. While Applesoft BASIC is slower than Integer BASIC, it has many features that the older BASIC lacks:

Conversely, Applesoft lacked the MOD (remainder) operator that had been present in Integer BASIC.

Microsoft licensed a BASIC compatible with Applesoft to VTech for its Laser 128 clone.[3]

Speed issues, features

Whereas Wozniak originally referred to his Integer BASIC as "Game BASIC," having written it so he could write a Breakout clone for his new computer,[1] few action games were written in Applesoft BASIC for several reasons:

Other language features:

Bugs

Due to a short-cut in the programming of the overflow test when evaluating 16 bit numbers, entering any number from 437760 to 440319 for a new line number at the BASIC prompt will cause Applesoft to crash, usually to a monitor prompt.[6] Entering 440000 at the prompt has been used to hack games that are protected against entering commands at the prompt after the program is loaded.

Early evolution

The original Applesoft, stored in RAM as documented in its Reference Manual of November 1977, has smaller interpreter code than the later Applesoft II, occupying 8½ kb of memory,[7] instead of the 10 kb used by the later Applesoft II. Consequently, it lacks a number of command features developed for the later, mainstream version:

as well as several the later version would have, that had already been present in Apple's Integer BASIC:

In addition, its low-resolution graphics commands have different names from their Integer BASIC/Applesoft II counterparts. All command names are of the form PLTx such that GR, COLOR=, PLOT, HLIN and VLIN are called PLTG, PLTC, PLTP, PLTH, and PLTV, respectively. The command for returning to text mode, known as TEXT in other versions, is simply TEX, and carries the proviso that it has to be the last statement in a program line.

The USR() function is also defined differently, serving as a stand-in for the absent CALL command. Its argument is not for passing a numerical value to the machine-language routine, but is instead the call-address of the routine itself; there is no "hook" to pre-define the address. All of several examples in the manual use the function only to access "system monitor ROM" routines, or short user-routines to manipulate the ROM routines. No mention is made of any code to calculate the value returned by the function itself; the function is always shown being assigned to "dummy" variables, which, without action to set a value by user-code, just receive a meaningless value handed back to them. Even accessed ROM routines that return values (in examples, those that provide the service of PDL() and SCRN() functions) merely have their values stored, by user-routines, in locations that are separately PEEKed in a subsequent statement.

Unlike in Integer BASIC and Applesoft II, the Boolean operators AND, OR and NOT perform bitwise operations on 16-bit integer values. If they are given values outside that range, an error results.

The terms OUT and PLT (and the aforementioned IN) appear in the list of reserved words, but are not explained anywhere in the manual.

Sample code

Hello World, with inverse video and bell character, run then listed

Hello World in Applesoft BASIC can be entered as the following:

 10TEXT:HOME
 20?"HELLO WORLD"

Multiple commands can be included on the same line of code if separated by a colon (:). The ? can be used in Applesoft BASIC (and almost all versions of Microsoft BASIC) as a shortcut for "PRINT", though spelling out the word is not only acceptable but canonical—Applesoft converted "?" in entered programs to the same token as "PRINT" (thus no memory is actually saved by using "?"), thus either appears as "PRINT" when a program is listed. The program above appears in a LIST command as:

 10  TEXT : HOME
 20  PRINT "HELLO WORLD"

[8]

When Applesoft II BASIC was initially released in mid-1978, it came on cassette tape and could be loaded into memory via the Apple II's machine language monitor. When the enhanced Apple II+ replaced the original II in 1979, Applesoft was now included in ROM and automatically started on power-up if no bootable floppy disk was present. Conversely, Integer BASIC was now removed from ROM and turned into an executable file on the DOS 3.3 disk.

BASIC for the Apple III

Microsoft and Apple each developed their own versions of BASIC for the Apple III computer. Apple III Microsoft BASIC was designed to run on the CP/M platform available for the Apple III. Apple Business BASIC, meanwhile, shipped with the Apple III. Donn Denman ported Applesoft BASIC to SOS and reworked it to take advantage of the extended memory of the Apple III.

Both languages introduced a number of new or improved features over Applesoft II, some of the same features as each other, and some unique to each. Both languages replace Applesoft II's single-precision floating-point variables using 5-byte storage with the somewhat-reduced-pecision 4-byte variables, while also adding a larger numerical format. Apple III Microsoft BASIC provides double-precision floating-point variables, taking 8 bytes of storage,[9] while Apple Business BASIC offers an extra-long integer type, also taking 8 bytes for storage.[10] Both languages also retain 2-byte integers, and maximum 255-character strings.

Other new features common to both languages include:

Differences of the same features:

Apple III Microsoft BASIC Apple Business BASIC
integer division operator \ (backslash) DIV
reading the keyboard without waiting INKEY$ function returns a one-character string representing the last key pressed, or the null string if no new key pressed since last reading KBD read-only "reserved variable" returns the ASCII code of the last key pressed; the manual fails to document what is returned if no new key pressed since last reading
reassigning a portion of a string variable MID$() assignment statement SUB$() assignment statement
determining position of text output POS() function to read horizontal screen position, and LPOS() function to read horizontal position on printer HPOS and VPOS assignable "reserved variables" to read or set the horizontal or vertical position for text screen output
accepting hexadecimal-format values "&H"-formatted expressions TEN() function to give numerical value from string representing hexadecimal
result of ASC("")

(null string operand)

causes an error returns the value −1

Features specific to each language are described separately below.

Apple III Microsoft BASIC additional new features

There is no support for graphics provided within the language, nor for reading analog controls or buttons; nor is there a means of defining the active window of the text screen.

Apple Business BASIC additional new features

Apple Business BASIC eliminates all references to absolute memory addresses. Thus, the POKE command and PEEK() function were not included in the language, and new features replaced the CALL statement and USR() function. Functionality of certain features in Applesoft that had been achieved with various PEEK and POKE locations is now provided by:

External binary subroutines and functions are now loaded into memory by a single INVOKE disk-command that loads separately-assembled code modules, listing the names of all files to be used. A PERFORM statement is then used to call an INVOKEd procedure by name, with an argument-list. INVOKEd functions would be referenced in expressions by EXFN. (floating-point) or EXFN%. (integer), with the function name appended, plus the argument-list for the function.

Graphics are supported with an INVOKEd module, with features including displaying text within graphics in various fonts, within four different graphics modes available on the Apple III, including the precursor of Apple IIe's double-high-resolution mode.

See also

References

  1. 1 2 Wozniak, Steve (2014-05-01). "How Steve Wozniak Wrote BASIC for the Original Apple From Scratch". Gizmodo. Retrieved 2 May 2014.
  2. Herzfeld, Andy "MacBasic – The Sad Story of MacBasic". http://www.folklore.org/StoryView.py?project=Macintosh&story=MacBasic.txt . Folklore.org. 2014 February 12
  3. Grevstad, Eric (1986-12). "Laser 128 / An Affordable Compatible". inCider. p. 58. Retrieved 29 June 2014. Check date values in: |date= (help)
  4. Applesoft II Basic Programming Reference Manual, Apple Computer, Inc., 1978
  5. 1 2 Applesoft BASIC Programmer's Reference Manual (for IIe only), Apple Computer, Inc., 1982
  6. http://www.txbobsc.com/scsc/scdocumentor/D912.html Disassembled ROM. See comments at $DA1E.
  7. Applesoft Extended Precision Floating Point Basic Language Reference Manual, Apple Computer, Inc., November 1977
  8. This article includes text from Everything2, licensed under GFDL.
  9. Apple III Microsoft BASIC Reference Manual, Microsoft Corporation, 1982
  10. Apple Business BASIC Reference Manual, Apple Computer, Inc., 1981

External links

This article is issued from Wikipedia - version of the Sunday, April 24, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.