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168 lines
4.1 KiB
Markdown
168 lines
4.1 KiB
Markdown
# LISP 1.5 implemented in PLASMA
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LISP interpreted on a bytecode VM running on a 1 MHz 6502 is going to be sssllllooooowwwww. So I called this implementation DRAWL in keeping with the speech theme. DRAWL represents an exploration REPL language for the PLASMA environment. It isn't meant to be a full-blown programming language, more of an interactive sandbox for playing with S-expressions.
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## Missing features of LISP 1.5 in DRAWL
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- General recursion. The 6502 architecture limits recursion (but see tail recursion below), so don't expect too much here
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- Many of the built-in functions from the LISP 1.5 manual. Most can be coded in LISP and loaded at startup
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However, the code is partitioned to allow for easy extension so some of these missing features could be implemented.
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## Features of DRAWL
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- 32 bit integers and 80 bit floating point with transcendental math operators by way of the SANE library
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- Tail recursion handles deep recursion. Check out [loop.lisp](https://github.com/dschmenk/PLASMA/blob/master/src/lisp/loop.lisp)
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- Fully garbage collected behind the scenes
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- Optionally read LISP source file at startup
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- The PROG feature now present!
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- Arrays of up to four dimensions
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- FUNCTION operation with bound variables
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- Additional testing/looping construct: IF, FOR, WHILE, UNTIL
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- Bit-wise logic operations on 32 bit integers
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- Hexadecimal input/output
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The DRAWL implementation comes with the following built-in functions:
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### Constants
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- T = True
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- F = False
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- NIL = NULL
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- SPACE = SPACE character on output
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- CR = Carriage Return character on output
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- CSET()
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- CSETQ()
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- DEFINE()
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### Function types
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- LAMBDA(...)
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- FUNARG() = List constructed by FUNCTION()
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- FUNCTION()
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### Predicates
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- ATOM()
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- EQ()
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- NOT()
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- AND(...)
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- OR(...)
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- NULL()
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### Misc
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- SET
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- QUOTE()
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- ARRAY()
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- TRACE() = Turn tracing on/off
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- GC() = Run garbage collector and return free memory amount
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- QUIT() = Exit REPL
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### List manipulation
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- CAR()
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- CDR()
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- CONS()
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- LIST(...)
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### Conditionals
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- COND(...)
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- IF()
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### Output
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- PRHEX() = Turn hexadecimal output on/off
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- PRI(...) = Print without newline
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- PRINT(...) = Print with newline
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- FMTFPI() = Floating point format integer digits
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- FMTFPF() = Floating point format fractional digits
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- PRINTER() = Turn printer echo on/off on slot#
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### Looping
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- FOR(...)
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- WHILE(...)
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- UNTIL(...)
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### Associations
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- LABEL()
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- SET()
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- SETQ()
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### Program feature
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- PROG() = Algol like programming in LISP
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- GO() = Goto label inside PROG
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- RETURN() = Return from PROG with value
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### Numbers
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- +(...)
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- -()
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- \*()
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- /()
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- REM()
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- NEG()
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- ABS()
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- \>()
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- <()
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- MIN(...)
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- MAX(...)
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### Integers
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- BITNOT() = Bit-wise NOT
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- BITAND() = Bit-wise AND
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- BITOR() = Bit-wise OR
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- BITXOR= Bit-wise XOR
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- SHIFT() = Bit-wise SHIFT (positive = left, negative = right)
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- ROTATE() = Bit-wise ROTATE (positive = left, negative = right)
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### Floating Point (from the SANE library)
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- PI()
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- MATH_E()
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- LOGB()
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- SCALEB_I()
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- TRUNCATE()
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- ROUND()
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- SQRT()
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- COS()
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- SIN()
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- TAN()
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- ATAN()
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- LOG2()
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- LOG2_1()
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- LN()
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- LN_1()
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- POW2()
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- POW2_1()
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- POWE()
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- POWE_1()
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- POWE2_1()
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- POW_I()
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- POWY()
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- COMP()
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- ANNUITY()
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LISP is one of the earliest computer languages. As such, it holds a special place in the anals of computer science. I've always wanted to learn why LISP is held in such high regard by so many, so I went about learning LISP by actually implementing a LISP interpreter in PLASMA. PLASMA is well suited to implement other languages due to its rich syntax, performance and libraries.
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## Links
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Here are some links to get you started.
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LISP 1.5 Manual: https://archive.org/details/bitsavers_mitrlelisprammersManual2ed1985_9279667
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LISP 1.5 Primer: https://www.softwarepreservation.org/projects/LISP/book/Weismann_LISP1.5_Primer_1967.pdf
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P-LISP Manual (newer than LISP 1.5): https://archive.org/details/gLISP/gnosisLISPManual
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Apple Numerics Manual (SANE): https://vintageapple.org/inside_o/pdf/Apple_Numerics_Manual_Second_Edition_1988.pdf
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Video showing DRAWL in action: https://youtu.be/wBMivg6xfSg
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Preconfigured PLASMA ProDOS boot floppy for DRAWL: https://github.com/dschmenk/PLASMA/blob/master/images/apple/DRAWL.po
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