EFRP Programming EventDriven Systems AssignmentFree

1
E-FRPProgramming Event-Driven SystemsAssignment-
Free

• Zhanyong Wan, Walid Taha, and Paul Hudak
• Yale University
• Department of Computer Science

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Motivating Problem

• Yale RoboCup Team

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Simple RoboCup Controller (SRC)
behavior event delay
0-100
duty cycle
desired speed
SRC
0/1
power
speed
count
IR
0-100
ClkFast
ClkSlow
IncSpd
DecSpd
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Green Boxes
event delay

• Reactive behaviors
• Output change triggered by event(s)
• Immediate reaction o changes when e occurs
• Delayed reaction o changes right after e occurs

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Yellow Boxes

• Non-reactive behaviors
• Not directly triggered by events
• Output is a pure function of input behavior(s)
• Output changes when and only when any of the
  inputs changes

i1
o
f(i1, i2)
o f(i1, i2)
i2
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Simple RoboCup Controller (SRC)
behavior event delay
0-100
duty cycle
desired speed
SRC
0/1
power
speed
count
IR
0-100
ClkFast
ClkSlow
IncSpd
DecSpd
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SRC in C

• Event handlers

init() ds s dc count power 0
onIncSpd() ds onDecSpd() ds--
onIR() s onClkFast() count
count gt 100 ? 0 count 1 power count lt
dc ? 1 0 onClkSlow() dc s lt ds ? dc
1 s gt ds ? dc 1 dc power
count lt dc ? 1 0 s 0
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SRC in C Problem 1

• Scattered definition

init() ds s dc count power 0
onIncSpd() ds onDecSpd() ds--
onIR() s onClkFast() count
count gt 100 ? 0 count 1 power count lt
dc ? 1 0 onClkSlow() dc s lt ds ? dc
1 s gt ds ? dc 1 dc power
count lt dc ? 1 0 s 0
duty cycle
desired speed
SRC
power
speed
count
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SRC in C Problem 2

• Code duplication

init() ds s dc count power 0
onIncSpd() ds onDecSpd() ds--
onIR() s onClkFast() count
count gt 100 ? 0 count 1 power count lt
dc ? 1 0 onClkSlow() dc s lt ds ? dc
1 s gt ds ? dc 1 dc power
count lt dc ? 1 0 s 0
duty cycle
desired speed
SRC
power
speed
count
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Source of the Problems

• Event-Oriented View

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SRC in C Problem 3

• Poor modularity

Change is global!
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Solution Behavior-Oriented View
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Our Contributions

• The E-FRP (Event-Driven Functional Reactive
  Programming) language
• Fits the model
• Behavior-oriented rather than event-oriented
• Doesnt suffer from the problems C has
• Formal semantics
• An E-FRP compiler
• Generates efficient C code for PIC16C66 MCU
• Provably correct
• Preserves semantics
• Resource bounded target code
• Optimizations

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E-FRP by Examples

• Immediate reaction
• Delayed reaction

• One definition for each block in diagram
• Formal syntax in the paper
• Non-reactive behavior

f(i, o-)
o
i
e
o init c on e gt f(i,o)
i1
f(i1,i2)
f(i, o-)
o
o
i
i2
e
o f(i1,i2)
o init c on e gt f(i,o) later
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What about Semantics?

• Operational semantics
• Input an (infinite) event sequence
• Output an (infinite) store sequence
• On an event, a program yields a store and is
  updated by a new program
• Details in the paper
• Important design choices
• No user defined events
• No simultaneous events
• Simplifies semantics
• Generates more efficient code

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SRC in Two Languages

• E-FRP
• ds init 0 on IncSpd gt ds1,
• DecSpd gt ds-1
• s init 0 on IR gt s1,
• ClkSlow gt 0 later
• dc init 0 on ClkSlow gt
• if s lt ds then dc1
• else if s gt ds then dc-1
• else dc
• count init 0 on ClkFast gt
• if count gt 100 then 0
• else count1
• power if count lt dc then 1
• else 0

• C
• init()
• ds s dc count power 0
• onIncSpd() ds
• onDecSpd() ds--
• onIR() s
• onClkFast()
• count count gt 100 ? 0
• count 1
• power count lt dc ? 1 0
• onClkSlow()
• dc s lt ds ? dc 1

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SRC in Two Languages
duty cycle
desired speed
SRC
power
speed
count

• E-FRP
• ds init 0 on IncSpd gt ds1,
• DecSpd gt ds-1
• s init 0 on IR gt s1,
• ClkSlow gt 0 later
• dc init 0 on ClkSlow gt
• if s lt ds then dc1
• else if s gt ds then dc-1
• else dc
• count init 0 on ClkFast gt
• if count gt 100 then 0
• else count1
• power if count lt dc then 1
• else 0

• C
• init()
• ds s dc count power 0
• onIncSpd() ds
• onDecSpd() ds--
• onIR() s
• onClkFast()
• count count gt 100 ? 0
• count 1
• power count lt dc ? 1 0
• onClkSlow()
• dc s lt ds ? dc 1

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SRC in Two Languages
duty cycle
desired speed
SRC
power
speed
count

• E-FRP
• ds init 0 on IncSpd gt ds1,
• DecSpd gt ds-1
• s init 0 on IR gt s1,
• ClkSlow gt 0 later
• dc init 0 on ClkSlow gt
• if s lt ds then dc1
• else if s gt ds then dc-1
• else dc
• count init 0 on ClkFast gt
• if count gt 100 then 0
• else count1
• power if count lt dc then 1
• else 0

• C
• init()
• ds s dc count power 0
• onIncSpd() ds
• onDecSpd() ds--
• onIR() s
• onClkFast()
• count count gt 100 ? 0
• count 1
• power count lt dc ? 1 0
• onClkSlow()
• dc s lt ds ? dc 1

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Compile E-FRP to C

• Compilation
• Data representation
• Each behavior variable x in E-FRP ? two global
  variable x and x in C
• Translation
• For each event in E-FRP
• Collect data dependencies
• Determine order for assignments
• Provably correct
• Optimizations

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Castling

• Uses knowledge about compiler
• Why is castling useful?
• Fewer right-hand-side uses of x
• Easier to eliminate x later

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Unoptimized Target Code for SRC

• Target code before optimization

onIncSpd() ds ds 1 power if count lt dc
then 1 else 0 ds ds power
if count lt dc then 1 else 0 onDecSpd() ds
ds - 1 power if count lt dc then 1 else 0
ds ds power if count lt dc then
1 else 0 onIR() s s 1 power if
count lt dc then 1 else 0 s s
power if count lt dc then 1 else 0
onClkFast() count count gt 100 ? 0
count 1 power count lt dc ? 1 0
count count power count lt dc ? 1
0 onClkSlow() s 0 dc s lt ds ? dc
1 s gt ds ? dc 1 dc power
count lt dc ? 1 0 s s dc dc power
count lt dc ? 1 0
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Optimized Target Code for SRC

• Target code after optimization

onIncSpd() ds ds 1 onDecSpd() ds
ds - 1 onIR() s s 1
onClkFast() count count gt 100 ? 0
count 1 power count lt dc ? 1
0 onClkSlow() dc s lt ds ? dc 1
s gt ds ? dc 1 dc power count lt dc ? 1
0 s 0
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Related Work

• Languages for event-driven systems

Languages for reactive systems
Declarative
Resource-bounded
Fit forevent-drivensystems
Esterel
FRP
RT-FRP
E-FRP
Lustre
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End of Talk

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