Little Rebol program that demonstrates using 'parse' to interpret some rudimentary Logo commands with a turtle and visual interface

turbol.reb

REBOL [
  title: "Rudimentary implementation of Logo Turtle"
  date: 2015-02-16
  author: "Martin Ceronio"  
]

{ Load the turtle image; you can find the original at https://edu.kde.org/images/icons/kturtle_32.png Thanks, KTurtle! }
turtle-img: do to-string debase
{make image! [32x32 #{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} #{
FFFFFFFFFFFFFFFFFFFF
FFFFFF000000000000FF
FFFFFFFFFFFFFFFFFFFF
FFFFFFFFFFFFFFFFFFFF
FFFFFFFFFF0300000000
00FFFFFFFFFFFFFFFFFF
FFFFFFFFFFFFFFFFFFFF
FFFFFFFFFFFFFF030000
000000FFFFFFFFFFFFFF
FFFFFFFFFFFFFFFFFFFF
FFFFFFFFFFFFFF000000
00000000000000FFFFFF
FFFFFFFFFFFFFFFFFFFF
FFFFFFFFFFFFFFFFFF00
000000000000010200FF
FFFFFFFFFFFFFFFFFFFF
FFFFFFFFFFFFFFFFFFFF
FF000000000001020304
00FFFFFFFFFFFFFFFFFF
FFFFFFFFFFFFFFFFFFFF
FFFFFF00000000010204
050600FFFFFFFFFFFFFF
FFFFFFFFFFFFFFFFFFFF
FFFFFFFFFF0000000203
0405000000FFFFFFFFFF
FFFFFFFFFFFFFFFFFF00
0000000000FFFF000000
04050607000000FFFF00
0000000000FFFFFFFFFF
FF000000000000FFFFFF
FF000506080900FFFFFF
FF000011121400FFFFFF
FFFFFF000000000000FF
FFFFFF000708090A00FF
FFFFFF000000000000FF
FFFFFFFFFFFFFF000000
00FFFF000000090A0B0C
000000FFFF00000000FF
FFFFFFFFFFFFFFFFFF00
000000FFFF0008090A0C
0D0E0F1000FFFF000000
00FFFFFFFFFFFFFFFFFF
FF000000000000000A0B
0C0D0E0F111200000300
040400FFFFFFFFFFFFFF
FFFFFFFFFFFF00080A0B
0C0D0E0F101112131416
1700FFFFFFFFFFFFFFFF
FFFFFFFFFFFFFFFF000A
0B0C0D0E101112131415
16171800FFFFFFFFFFFF
FFFFFFFFFFFFFF000000
000C0D0E0F1011121315
161718191A00000000FF
FFFFFFFFFFFFFFFFFF00
000B0C0E0F1011121314
15161718191B1C1D1E00
00FFFFFFFFFFFFFFFFFF
FF00000D0E0F10111214
15161718191A1B1C1D1E
200000FFFFFFFFFFFFFF
FFFFFF00000F10111213
14151617181A1B1C1D1E
1F20210000FFFFFFFFFF
FFFFFFFFFF0000101213
1415161718191A1B1C1D
1F202122230000FFFFFF
FFFFFFFFFFFFFF000012
1314151618191A1B1C1D
1E1F20212224250000FF
FFFFFFFFFFFFFFFFFF00
001415161718191A1B1C
1E1F2021222324252600
00FFFFFFFFFFFFFFFFFF
FF0000000018191A1B1C
1D1E1F20212324252600
000000FFFFFFFFFFFFFF
FFFFFFFFFFFF00191A1C
1D1E1F20212223242526
2800FFFFFFFFFFFFFFFF
FFFFFFFFFFFFFFFF0000
001D1E1F202223242526
27000000FFFFFFFFFFFF
FFFFFFFFFFFFFF000000
00000000202122232425
272800000000000000FF
FFFFFFFFFFFFFFFFFF00
000000FF000022232425
262728290000FF000000
00FFFFFFFFFFFFFFFF00
0000000000FF00000000
0000000000000000FF00
0000000000FFFFFFFFFF
FF000000000000FFFFFF
FFFFFFFFFFFFFFFFFFFF
FF000000000000FFFFFF
FFFFFF000000000000FF
FFFFFFFFFFFFFFFFFFFF
FFFFFF000000000000FF
FFFFFFFFFF0000000000
00FFFFFFFFFFFFFFFFFF
FFFFFFFFFF0000000000
00FFFFFF
}]}

{ This represents the "API" of the turtle, including the parse rules for commands issued to it
  It also translates commands into drawing commands for VID }
turtle: make object! [
  field-size: 400x400
  direction: 0
  location: field-size / 2
  command-history: copy []
  draw-commands: copy []
  pen-is-down: true
  last-error: none

  parse-rules: [
    some [
      ['fd | 'forward] set value integer! (move-by value) |
  	  ['bk | 'back] set value integer! (move-by value * -1) |
	  'left set value integer! (turn value * -1) |
	  'right set value integer! (turn value) |
	  'color set value word! (set-color value) |
  	  'home (reset) |
  	  ['pu | 'penup] (pen-is-down: false) |
  	  ['pd | 'pendown] (pen-is-down: true) |
  	  'clear (clear) |
	  'repeat set value integer! set blk block! (repeat none! value [ parse blk parse-rules ]) |
  	  set word word! (last-error: to-string compose ["unknown word " (word)]) break 
    ]    
  ]
  
  translate-fld: func [location [pair!]] [
    location/y: field-size/y - location/y 
    location 
  ]  
  
  turn: func [degrees [integer!]] [
    direction: direction + degrees
	degrees: degrees // 360
  ]
  
  set-color: func [color] [
    append draw-commands compose [ pen (color) ]
  ]
  
  reset: func [] [
    direction: 0
	location: field-size / 2
  ]
  
  clear: func [] [
    reset
	pen-is-down: true
	draw-commands: copy []
	command-history: copy []
  ]
  
  { Stores a command and parses it, updating the state and possibly updating draw commands }
  command: func [cmd [string!]] [
    append/only command-history cmd
	process-command cmd
  ]
  
  { Moves the turtle in the direction it is currently facing by the distance given; also generates draw commands }
  move-by: func [distance [integer!]] [
    delta: to-pair compose [(to-integer (sine direction) * distance) (to-integer  (cosine direction) * distance)]
	if pen-is-down [ append draw-commands compose [line (translate-fld location) (translate-fld location + delta)] ]
	location: location + delta
  ]
  
  process-command: func [cmd [string!]] [
    last-error: none
	parse to-block cmd parse-rules
  ]
  
  redraw-commands: func [] [
    last-error: none
    draw-commands: copy []
	reset
	for-each cmd command-history [
	  process-command
	  if last-error [ break ]
	]
  ]
  
]

{ User Interface }
view layout [

  across
  tfield: box white turtle/field-size effect [
    draw [ pen red translate 200x200 scale .75 .75 rotate turtle/direction image turtle-img -16x-16 16x16 ]
  ]
  
  chistory: text-list data turtle/command-history
  
  return
  
  cfield: field [ 
    turtle/command cfield/text
	tfield/effect/draw: copy turtle/draw-commands
	append tfield/effect/draw compose/deep [ translate (turtle/translate-fld turtle/location) scale .75 .75 rotate (turtle/direction) image turtle-img -16x-16 16x16 ]
	if turtle/last-error [ alert turtle/last-error ]
	show tfield   { Update the drawing area }
	show chistory { Update the history text-list }
	cfield/text: none
	focus cfield
  ]
  
  do [
    
    focus cfield
  ]
 
]