Back to the BASICs

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# Back to the BASICs
## Jan 'half/byte' Krutisch
## Baltic Ruby 2024
---
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# Back to the BASICs
## Jan 'half/byte' Krutisch
## Baltic Ruby 2024
---
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# Let's go back in time
---
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# 1985

???

Age hook, but skip the joke

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background-image: url(img/altair8800.png)
# 1975

???
- Altair 8800
- Microsoft BASIC by Bill Gates, Paul Allen, Monte Davidoff
---
background-image: url(img/altair_basic_better.jpg)

---
# First wave of home computers
- Apple II (1977)
- Commodore PET, VIC-20, C-64 ('77, '80, '82)
- TRS-80 (1977 / 1980)
- Atari 400/800 (1979)
- Sinclair ZX80, ZX81, Spectrum (1980, '81, '82)
- Acorn BBC Micro (1981)
- Amstrad CPC (1984)
- ...
---
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# Why I like these systems
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# Simple
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# Complete understanding
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background-image: url(img/amiga.png)
# 1985
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background-image: url(img/c64.png)
# Commodore C64

???

Also came with Microsoft BASIC

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# BASIC
---

## Beginners
## All purpose
## Symbolic
## Instruction
## Code
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# Some BASIC facts

???

- created in 1963 at Dartmouth College (NH)
- by John G. Kemeny & Thomas E. Kurtz
- Originally a compiled language for multi-user systems
- Later: Interpreter for smaller computers
- Micro-Soft BASIC for home computers (Written by Bill Gates, Paul Allen and Monte Davidoff)
- Most home computers use some variant of MS BASIC
---

background-image: url(img/c64_basic.png)

---
# A BASIC example
```basic
10 FOR I = 1 TO 200 STEP 0.2
20 GOSUB 100
30 PRINT SPC(II);"#"
40 NEXT I
50 END
100 II = INT((SIN(I) + 1)*20)
110 RETURN
```
---
# What stands out
```basic
10 FOR I = 1 TO 200 STEP 0.2
20 GOSUB 100
30 PRINT SPC(II);"#"
40 NEXT I
50 END
100 II = INT((SIN(I) + 1)*20)
110 RETURN
```
---
# BASIC IS LOUD!!!1!!
```basic
10 FOR I = 1 TO 200 STEP 0.2
20 GOSUB 100
30 PRINT SPC(II);"#"
40 NEXT I
50 END
100 II = INT((SIN(I) + 1)*20)
110 RETURN
```
---
# Short variable names
```basic
10 FOR I = 1 TO 200 STEP 0.2
20 GOSUB 100
30 PRINT SPC(II);"#"
40 NEXT I
50 END
100 II = INT((SIN(I) + 1)*20)
110 RETURN
```
---
# All Variables are global
```basic
10 FOR I = 1 TO 200 STEP 0.2
20 GOSUB 100
30 PRINT SPC(II);"#"
40 NEXT I
50 END
100 II = INT((SIN(I) + 1)*20)
110 RETURN
```
---
# No "functions", no args
```basic
10 FOR I = 1 TO 200 STEP 0.2
20 GOSUB 100
30 PRINT SPC(II);"#"
40 NEXT I
50 END
100 II = INT((SIN(I) + 1)*20)
110 RETURN
```
---
# Explicit line numbers
```basic
10 FOR I = 1 TO 200 STEP 0.2
20 GOSUB 100
30 PRINT SPC(II);"#"
40 NEXT I
50 END
100 II = INT((SIN(I) + 1)*20)
110 RETURN
```
---
background-image: url(img/teletype.png)
---
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<video src="videos/basic_plus_monitor.mp4" controls="controls" height="681">

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![](img/basic_in_mem.drawio.png)

???
- zero as delimiter
- pointer to next line
- line number
- token
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# Modern development workflow

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# Let's find out what's going on
---
background-image: url(img/c64_insider_book.png)

???

A book from 1988

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background-image: url(img/lee_davison_commentary.png)

---
background-image: url(img/pagetable.png)
---
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# Behold: 6502 assembler
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# Don't be afraid
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# First part of
# "BASIC warm start"
## (MAIN:)
---
# BASIC warm start
<table class="disassembly">
<tr>
<td class="routine-comment" colspan="5">
<div class="details">
<div class="paragraph">
the warm start vector is initialised to point here
</div>
</div>
</td>
</tr>
<tr>
<td class="address-2"><span id="A483"></span>A483</td>
<td class="bytes">20 60 A5</td>
<td class="instruction">JSR <a href="A560.html">$A560</a></td>
<td class="comment-1" rowspan="1">call for BASIC input</td>
</tr>
<tr>
<td class="address-1"><span id="A486"></span>A486</td>
<td class="bytes">86 7A</td>
<td class="instruction">STX $7A</td>
<td class="comment-1" rowspan="1">save BASIC execute pointer low byte</td>
</tr>
<tr>
<td class="address-1"><span id="A488"></span>A488</td>
<td class="bytes">84 7B</td>
<td class="instruction">STY $7B</td>
<td class="comment-1" rowspan="1">save BASIC execute pointer high byte</td>
</tr>
<tr>
<td class="address-1"><span id="A48A"></span>A48A</td>
<td class="bytes">20 73 00</td>
<td class="instruction">JSR $0073</td>
<td class="comment-1" rowspan="1">increment and scan memory</td>
</tr>
<tr>
<td class="address-1"><span id="A48D"></span>A48D</td>
<td class="bytes">AA</td>
<td class="instruction">TAX</td>
<td class="comment-1" rowspan="1">copy byte to set flags</td>
</tr>
<tr>
<td class="address-1"><span id="A48E"></span>A48E</td>
<td class="bytes">F0 F0</td>
<td class="instruction">BEQ <a href="A474.html#A480">$A480</a></td>
<td class="comment-1" rowspan="1">loop if no input</td>
</tr>
<tr>
<td class="routine-comment" colspan="5">
<span id="A490"></span>
<div class="comments">
<div class="paragraph">
got to interpret the input line now ....
</div>
</div>
</td>
</tr>
<tr>
<td class="address-1"><span id="A490"></span>A490</td>
<td class="bytes">A2 FF</td>
<td class="instruction">LDX #$FF</td>
<td class="comment-1" rowspan="1">current line high byte to -1, indicates immediate mode</td>
</tr>
<tr>
<td class="address-1"><span id="A492"></span>A492</td>
<td class="bytes">86 3A</td>
<td class="instruction">STX $3A</td>
<td class="comment-1" rowspan="1">set current line number high byte</td>
</tr>
<tr>
<td class="address-1"><span id="A494"></span>A494</td>
<td class="bytes">90 06</td>
<td class="instruction">BCC <a href="A49C.html">$A49C</a></td>
<td class="comment-1" rowspan="1">if numeric character go handle new BASIC line</td>
</tr>
<tr>
<td class="routine-comment" colspan="5">
<span id="A496"></span>
<div class="comments">
<div class="paragraph">
no line number .. immediate mode
</div>
</div>
</td>
</tr>
<tr>
<td class="address-1"><span id="A496"></span>A496</td>
<td class="bytes">20 79 A5</td>
<td class="instruction">JSR <a href="A579.html">$A579</a></td>
<td class="comment-1" rowspan="1">crunch keywords into BASIC tokens</td>
</tr>
<tr>
<td class="address-1"><span id="A499"></span>A499</td>
<td class="bytes">4C E1 A7</td>
<td class="instruction">JMP <a href="A7AE.html#A7E1">$A7E1</a></td>
<td class="comment-1" rowspan="1">go scan and interpret code</td>
</tr>
</table>
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# .opcode[JSR] .arg[$A560]
## Jump to SubRoutine
### Push return address on stack
---
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# What does .arg[$A560] do?
## Waits for input
## X, Y contain buffer address
## Ends with .opcode[RTS]
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# .opcode[RTS]
## ReTurn from Subroutine
## Pops return address on stack
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# What's X and Y?
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# Registers
.contain[![](img/registers.drawio.png)]
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# .opcode[STX] .arg[$7A]
# .opcode[STY] .arg[$7B]
## SToreX, SToreY
### stores register in memory
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# Odd address much?
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# Zeropage
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# .opcode[JSR] .arg[$0073]
### jumps to CHRGET
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# CHRGET?
### increments pointers in .arg[$7A], .arg[$7B]
### reads character there into A
### Sets a couple of flags
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# .opcode[TAX]
## Transfer A to X
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# .opcode[BEQ] .arg[$A480]
## Branch if EQual
### If zero flag is set, branch to relative address
### (Actual byte code: .bytes[F0 F0])
### .bytes[FO] = -16
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# Yeah, but, why?
## If read byte is zero:
## line was empty, so restart
---
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# .opcode[LDX] .arg[\#$FF]
## LoaDX
### Load immediate value into X
### X = -1
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# .opcode[STX] .arg[$3A]
### .arg[$3A] is current BASIC line number
### -1 signifies immediate mode
---
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# .opcode[BCC] .arg[$A49C]
## Branch if Carry Clear
### Carry flag usually for arithmetic operations

???

CHRGET sets carry if not a digit character

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# .opcode[JSR] .arg[$A579]
### Jump to tokenizer (CRUNCH)
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# .opcode[JMP] .arg[$A7E1]
## JuMP
### (No address pushed on stack)
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# .arg[$A7E1] is interpreter start point
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# Let's turn it into Ruby
---

```ruby
loop do
  begin
    line = @input.readline.strip
    parse(line)
  rescue BasicError => e
    @error.puts e.message
    @output.puts "READY."
  end
end

def parse(line)
  if line[0] =~ /\d/
    parse_line(line)
  else
    parse_direct(line)
  end
end
```

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# A few core concepts
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# Tokenizer
## CRUNCH:
---
# Find token (pseudocode)
```ruby
buffer = input
pos = 0 # position in pointer
token = 0
n = 0

loop do
  if token[i][n] == buffer[pos + n]
    token += 1
    n = 0
  else
    return token
  end
end
```
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# ! TRUTH / 2

???

Not even half the truth

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# Interpreter
## NEWSTT:
---
# Interpreter
1. look for token
2. lookup routine in table
3. call routine
4. rinse, repeat
---
# Let's PRINT
```basic
10 PRINT (2 + 2) * 5 + SIN(XY)
```
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# What shall we PRINT?
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# Formula Evaluation
## FRMEVL:, EVAL:
---
# Expression evaluation
```ruby
(2 + 2) * 5 + SIN(XY)
```
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<video src="videos/frmevl.mp4" controls="controls" height="681">
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# This nearly broke me
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# Ruby BASIC?
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# Roughly 1000-1500 lines
## (Of terrible ruby code)
## codeberg.org/halfbyte/ruby-basic

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# DEMO
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<video src="videos/ruby_basic.mp4" controls="controls" height="681">

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# What did I learn
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# Microsoft BASIC
# is
# a work of art
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# A very different world
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# Hard to transfer to Ruby
## (sometimes)
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# Global State is good, actually
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# Global State is good, actually
## (sometimes)
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# Complexity
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# What are we doing?
---
background-image: url(img/book_stack.png)

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# So many CPU cycles lost

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# So much Energy spent
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## cough, LLMs, cough
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## I don't want to go back
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## BUT: Be more aware?
---
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## What is your impact?
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## What are the incentives?
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## At least: Don't pile on
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# Acknowledgements
---
# Michael Steil
# Lee Davison
# The VICE team
# My Betatesters
## (aka RubyUnconf)
---
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# Jan Krutisch
## Co-Founder of Depfu.com
## Freelance Web Developer
## Digital Artist
## Looking for work
## @halfbyte@ruby.social
## https://halfbyte.me
# Thank you!