Lego/Scheme

1
Lego/Scheme

• By Rusty Burchfield and Brent Hepburn

2
Background

• Limited implementation of Scheme for the standard
  firmware
• Developed at Indiana University by three CS
  undergraduates
• Developed start to finish in three days

3
Environment

• Petite Chez Scheme 6.1
• LegoScheme compiler
• LegoScheme source
• Lego Mindcontrol
• Visual Basic output from LegoScheme

4
Features

• 10 concurrent tasks
• Support for most built-in scheme functions
• Support for lambda definitions
• Functions defined for direct interaction with RCX

5
Limitations

• Requires Lego Mindcontrol
• Tail-recursive ONLY and without parameters
• Limited support for bindings
• Only 8 functions
• Only 30 signed integers available
• Concurrency issues

6
Example

• (define task_zero
• (lambda ()
• (setup-sensor 1 'reflection 'percent)
• (set-engine-direction "02" 'forward)
• (set-engine-speed "02" 4)
• (set-engine-on/off "02" 'on)
• (task_one)
• (task_two)
• (task_three)))
• (define task_one
• (lambda ()
• (let ((x (read-from-sensor 0)) (y
  (read-from-sensor 2)))
• (if ( x t)
• (set-engine-on/off "02" 'off))
• (if ( y t)
• (flip-engine-direction "02"))
• (task_one))))

• (define task_two
• (lambda ()
• (wait 500)
• (flip-engine-direction "0")
• (wait 200)
• (flip-engine-direction "0")
• (wait 500)
• (flip-engine-direction "2")
• (wait 200)
• (flip-engine-direction "2")
• (task_two))
• (define task_three
• (lambda ()
• (let ((z (read-from-sensor 1)))
• (if (gt z 50) (play-system-sound 'fast-slide-up)
  (task_three)))))

7
Conclusion

• Difficult to use
• Many restrictions
• Hard to setup
• Lacking the power of Scheme

8
Resources

• References
• http//www.cs.indiana.edu/mtwagner/legoscheme/
• http//home.zonnet.nl/ericbrok/legomind/projects/r
  obo/mindcontrol.htm
• More Information
• http//www.cs.rit.edu/bah5108/