Transcript Functional Reactive Python On Introducing CS to High School

Functional Reactive Python
On Introducing CS to High School
Students
John Peterson
Western State College
Gunnison, CO
Goals
• Get high school students excited about
CS with a 1 week summer camp
• Bring them to Gunnison in the summer
Use video gaming as the bait
• Lots of outdoor activity
• Integrate Math / Physics into the
program
Objectives
• Teach basic principles – avoid putting
too much “in a can” or just doing drag &
drop / menu pulling (Not Alice)
• Avoid big chunks of code – no time to
teach software engineering
• Lots of small projects rather than one
big one
• Don’t hide from basic math / physics
• Use freely available software
Declarative Language Research
High school students are the best
audience I’ve ever had for exploring new
programming styles
• No pre-conceived notions about how to
program
• Eager to learn
• Will tell you what they think
The Game Engine
After considering a few possibilities, we
settled on the Panda3D game engine.
• Good support from CMU
• Python is a good instructional language
• All the basic features we needed were
covered
Modeling
We also chose to cover 3-D modeling a bit. We
used Blender but this had some problems
interacting with Panda:
• Texture loss (we never figured this out)
• Lack of support for joints / animations in the
files exported to Panda
• Poorly adapted to the Windows environment
In spite of this, many students spent a lot of
time building Blender models.
Student Work
While building these 3-D models isn’t
programming, it did help us get
accustomed to working in 3 space and
allowed students to personalize their 3-D
worlds.
Software Issues
Our goal was not to teach any specific
language or software system
We wanted every program to be as
declarative as possible: elegant and
compact
FRP (Functional Reactive Programming)
was used to hide time flow from the
students
Plan A
Write a custom front end (in Haskell of
course) to allow domain-specific
semantics and notations, provide
compile-time type safety, and give
appropriate error messages.
• Probably the right thing to do
• Not enough time!
• Doesn’t solve the debugging problem
• Need to build custom IDE
Plan B
Attempt to recreate FRP using Python
libraries.
• Able to use existing IDE (Pydev in
Eclipse), good debugger
• Python has lambda (just uglified lisp
after all)
• Students are likely to run into Python
later
• Much less work!!
Programming Style
Create factory functions for all game objects
(models, lights, gui controls, camera) – these
return an object “handle”
Use python keywords and good defaulting to
avoid complexity in the factory
“Moving parts” are defined by reactive signals
Signals can be defined separately to allow
circular reference
Use signals like “time” to get motion
Functional Reactive Programming
This is work I did back in the Yale (yuck!)
days.
The big idea is to hide time flow – no
event handles, explicit updating.
A “signal” (reactive value) is something
that seems to mutate on its own as time
progresses. Time flow becomes implicit.
Example: Moving Bear
from Panda import *
begin()
p = pandaBear()
p.position = P3(sin(time), 3, cos(time))
world.cameraPos = P3(0,-3,0)
start()
Teaching points: sin / cos, coordinate system, trajectories
Demo1.py
More Positioning
p1 = pandaBear()
p2 = pandaBear()
def f(t):
return P3(sin(t), 3, cos(t))
p1.position = f(time)
p2.position = f(time + pi)
p1.HPR = P3(time*2,0,0)
p2.scale = 0.2 * (5 + sin(2*time))
world.cameraPos = P3(0,-4,0)
Demo2.py
Adding Controls
Panda3d has lots of user interface devices. We
wrapped these up in FRP style to make them
easy to use.
h = hangglider()
Text("Use slider to adjust heading")
s = Slider(max = 2*pi)
Text(s.value)
h.position = P3(sin(time), 3, cos(time))
h.HPR = P3(s.value, 0, 0)
world.cameraPos = P3(0,-5,0)
Demo3.py
Teaching Math
A great thing about 3-D gaming is that
you can’t hide from math! Students
needed to pick this up fast.
We covered linear interpolation, basic
trig, paths, periodic functions, and
vector arithmetic (Thanks to Andy Keck
for being a great math teacher!)
We didn’t shy away from calculus – here’s
an example using derivatives.
Point Where You Go
Text("Plane circles while pointing forward")
p = boeing707()
b = P3C(3, time, sin(time*3))
p.position = b
db = deriv(P3(0,0,0), b)
hpr = P3toHPR(db) # Explained in lecture
p.HPR = P3(getX(hpr)-radians(90),-getY(hpr),
0)
world.cameraPos = P3(0,-10,1)
Demo4.py
Teaching Programming
We also wanted to teach basic ideas in
programming
Function definition was easy
We used for loops which arranged objects
in various patterns to talk about
conditional behavior, nested loops,
arrays, and random numbers
Exploding Balls
mycolors = [red, blue, green, yellow, purple, brown, white, black]
bagOfBalls = []
endPos = []
world.cameraPos = P3(0,-30,0)
random.seed()
explodeSpeed = 3 #.1 is very slow, 10 is very fast
for p in range(0,getRand(50,88)):
theColor = mycolors[getRand(0,7)]
if getRand(0,1) == 1:
bagOfBalls.append(volleyBall(color = theColor))
else:
bagOfBalls.append(soccerBall(color = theColor))
endPos.append(P3(getRand(-5,5), getRand(-5,5), getRand(-5,5)))
startPos = P3(0,0,0)
for index in range(0, len(endPos)):
d = endPos[index]
bagOfBalls[index].position = startPos + time*explodeSpeed*d
Demo5.py
Teaching Physics
Finally, we were able to get to some simple physics.
Here’s a bouncing ball:
def launch(p0, v0):
a = P3(0,0,-g)
v = v0 + integral(a)
p = p0 + integral(v)
return react(p, when(getZ(p) < 0, bounce, p, v))
def bounce(p0, v0):
return launch(P3(getX(p0), getY(p0), -getZ(p0)),
0.9*P3(getX(v0), getY(v0),
-getZ(v0)))
And the Roller Coaster
def f((t0, p0, v0), t1):
deltaT = t1 - t0
pe = scaleP3(deltaT, v0) + p0
p1 = P3(getX(pe), getY(pe), coasterPath(getX(pe)))
dir = p1 - p0
oldv = absP3(v0)
deltaz = getZ(p1) - getZ(p0)
s1 = oldv*oldv - 2 * g * deltaz
if s1 < 0:
newv = - sqrt(-s1)
else:
newv = sqrt(s1) * 0.999
v1 = scaleP3(newv, normP3(dir))
return ((t1, p1, v1), p1)
Demo6.py
Roller Coaster Notes
We covered the basic physics to make
this understandable
Students can explore changes to the
physical laws
Needed to “crack open” the underlying
signal extrapolation function. That was
tough since you see the signal state and
delta t. But you can also use this to
explain how integral and derivitave work
Panda Effects
Effects are fun for the students even
though they don’t contribute to the
core subject material.
We did lighting, particle effects
(explosions, sparkles, flames, ..), and
retexturing
Check out our disco
Demo7.py
Character Animation
Panda has a number of built-in jointed
characters. These are easy to control –
they have additional signals to set joint
angles.
What we didn’t do was introduce a way to
create animations easily. No easy way
to save a pose or sequence poses.
Games???
OK – I haven’t showed you any games. No
paddleball or asteroids or shooting
gallery or space invaders or doom.
Why? Because we didn’t get them
working yet. There was plenty to do
without gaming but next time this needs
to be fixed.
There were FRP problems, notational
problems, and time problems.
Game Engine Issues
• Any game engine has a huge API – it’s a lot of
work to build on such a big base
• Need to “normalize” existing models. We
wanted to use a common size / orientation so
students could swap models easily.
• No 3-D design environment for positioning
models or creating animations.
• Many high level abstractions are hard to
encapsulate. We avoided many of these
(collisions, tasks, animations).
Things the Worked
• Gaming as a way to unify math, cs, and physics
• Wide appeal – gamers and non gamers both
had fun
• Lots of assistants – kept students from
getting frustrated (thanks to Kate, Darek,
and Stephan)
• FRP made programs small and easily
understood
• Great source of projects for CS students
• Summer employment for CS students
Things That Didn’t Work Well
• Blender (too complex, importing
problems)
• FRP “in the large” – not sure how to do
this yet
• Python – not really a great language for
non-programmers. Notational issues
kept coming up (no user-definable infix
operators, couldn’t get field selection to
lift, overloading problems, …)
For Next Year
• More gaming!
• Better publicity – it’s hard to get students in the
door.
• Better software – too much time in the debugger,
poor notations, no type checking
• Better preparation – more examples, better lesson
planning (especially for math / physics integration
into the CS stuff)
• Music videos – this is something that we definitely
need to get to that leads nicely up to games. We
used Haskore to teach music but didn’t get the sound
to synch correctly with the action
Programming Language Issues
Making time flow implicit is a big win.
Laziness is crucial. We spent way to much time
having to re-invent lazy evaluation. Forward
reference was a big problem
Python’s O-O system kept getting in the way
Python lacks the syntactic flexibility that we
really needed
Good type systems make things a LOT easier.
We did some “load time” type checking but
didn’t get full H-M. Students didn’t
understand the debugger.
Multi-Disciplinary Education
CS instruction suffers from tunnel vision – we don’t do a
good job with students that are not going all the way
into CS.
Integrating the math and physics into our curriculum
broadens the appeal and sends a message to future
CS students
The creative side of CS is often hidden in CS1 – the
game engine gives us a chance to work in a more
creative environment
We were able to cover a wide range of math – not just
one specific topic. The visual nature of the system
helps a lot.
We hope to sell this beyond just CS instruction
Conclusions
Game engines are an appealing way to get students in
the door to CS departments
The broad range of topics helped keep all of the
students on board
3-D modeling was a nice contrast to programming – it let
students blow off steam when programming got hard
CS needs to better serve students in other disciplines
We need to get students interested in CS earlier
The 2 girls at the camp enjoyed it as much as the hard
core gamers.
Scenes from Camp
The Last Conclusion
A good recreational program will make
students forget the frustration of
software development.