Proto Quick Start
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1. is true returns the result of the true expression otherwise returns the result of the false expression The true and false expressions must return the same type if test true false Restricts execution to subspaces based on test Where test is true the true expression is evaluated where test is false the false expression is evaluated The true and false expressions must return the same type State Because Proto is a purely functional language we create state using feedback loops A state variable is initialized at some value then evolves that value forward in time In regions where the feedback loop is not evaluated the state variable is reinitialized resuming evolution when the feedback loop begins to be evaluated again For example the expression rep t 0 t dt creates a timer that returns how long evaluation has been proceeding at each device letfed var init evolve body Creates a state variable for each var var is initially bound to the value of expression init and at each time step the state is evolved forward using expression evolve The body is evaluated within an extended scope including the state variables In the evolve expression each var is bound to an old value and dt is set to the time since the last step All init and evolve expressions are evaluated in parallel so no variable can reference another value in its init but variables can use one another s old values in their evolve sta2. Proto Quick Start By the authors of MIT Proto Last Updated November 6 2010 This is a quick start guide for Proto giving a quick tour of commonly used features of the language and simulator for people who are already comfortable with distributed programming languages For installation instructions see the README For a tutorial on the Proto language see the document Thinking In Proto For a reference to the Proto language see the Proto Language Reference For a usee manual for the simulator see the Proto Simulator User Manual For information on how to extend the functionality of the simulator see the MIT Proto Developers Guide 1 Credits for Proto The Proto language was created in partnership by Jonathan Bachrach and Jacob Beal As they created the language Jonathan created the first implementation of MIT Proto including the first compiler kernel simulator and embedded device implementations Since that time Jake and other contributors have built on the work begun by Jonathan MIT Proto also includes contributions from alphabetically Aaron Adler Geoffrey Bays Anna Der bakova Nelson Elhage Takeshi Fujiwara Tony Grue Joshua Horowitz Tom Hsu Kanak Kshetri Prakash Manghwani Dustin Mitchell Omar Mysore Maciej Pacula Hayes Raffle Dany Qumsiyeh Omari Stephens Mark Tobenkin Ray Tomlinson Kyle Usbeck Dan Vickery The Protobo platform code in platforms protobo also includes Topobo related code from alphabeti cally Mi
3. city Argument rad N Radius of a device body defaults from the initial distribution bounds 0 087 width x height n Argument w Key w Use walls to keep devices inside the initial distribution bounds Argument m Key m Enable movement toggled by key Sensors and Actuators Argument probes N Key p Display the first N of the three probes The p key cycles through how many are shown Argument 1 Key L Display LEDs toggled by key Key t Toggle user sensor 1 on selected devices Key y Toggle user sensor 2 on selected devices Key u Toggle user sensor 3 on selected devices
4. ctors to neighbors respectively e min hood max hood all hood any hood int hood summarize a field into a scalar that is respec tively minimum maximum for all existence and integral over the values of the field fold hood fold base value Collects value from each of the neighbors then folds these into a summary value using fold to combine elements into base one at a time Capable of violating the continuous space time abstraction Sensor and Actuators Actuators reset themselves to a null value whenever they are not actively being invoked Thus for example if sense 1 mov tup 2 red tup 1 will cause devices move to the right only when sense 1 is true and to turn on their red LED only when sense 1 is false mov velocity Attempt to move at velocity The return echoes velocity red n Set red LED to intensity n Intensity ranges from 0 to 1 but overloading of display can show values outside this range The return echoes n green and blue are identical but set the green and blue LEDs instead probe value i Posts value to the ith probe valid indices are 0 to 2 sense i Returns the ith user sensor value coord Returns the device s estimated coordinates hood radius Returns the maximum expected range at which devices can communicate Library Functions These are not primitive functions but are frequently used building blocks which have been included in Proto s distribution librar
5. ent f Key f Full screen display toggled by key Key z Reset display to initial view Key ARROW KEYS Shift simulation display in the direction of the arrow in the simulation s coordinate system Mouse LEFT DRAG Rotate display Mouse RIGHT DRAG Zoom display toward center zooms out away zooms in Selection Mouse LEFT CLICK Select the devices clicked on Mouse RIGHT CLICK Select then print the state of the selected device s to standard out Mouse SHIFT LEFT DRAG Toggle the selection of all devices in a rectangular display region Mouse SHIFT RIGHT DRAG Move selected devices Device Distribution Simulations are created with n devices distributed through a bounded 2D or 3D volume according to one of several distribution rules Argument n N Number of devices Argument 3d Use a 3D distribution default is 2D Argument DD grid Distributes devices in a grid rathen than uniformly randomly Unit Disc Radio Communication The default communication model connects all devices less than some fixed distance apart Argument r N Transmission range for radio default 15 Argument ns N Set transmission range to get an expected neighborhood size of N Overrides r Argument c Key c Display network connections toggled by key Dynamics The default physics package simple dynamics is a simple vector stepping system that does not handle collisions and allows instantaneous shifts in velo
6. hese into a field of boolean numbers which is true at approximately 10 devices The once function wrapped around this says to do this once and remember the result Then we feed this boolean field into the gradient function which finds the distance from each device to the nearest device with a true value that is the nearest one that picked a random number less than 0 01 Finally these distances are fed to the red LED actuator that produces those dots on the screen If you zoom in one the blue numbers you ll see that the dots float above the number at a height equal to the number The blue numbers are the output of the Proto expression and are visible because of the v you can hit n to turn them on and off The LEDs are visible because of the 1 and you can use L to turn them on and off 3 Proto Language Essentials Here are some essentials to the Proto language along with the most frequently used functions Evaluation Proto is a purely functional language Proto is written using s expressions in a manner very similar to Scheme Evaluating a Proto expression produces a program a dataflow graph that may be evaluated against a space to produce an evolving field of values at every point on the space Data Types All Proto expressions produce fields that map every point in space to a value The values produced are categorized into four basic types fields lambdas tuples and scalars A number is a scalar or vector tuple with scalar va
7. ke Fleder Limor Fried Josh Lifton Laura Yip 2 Smoke Test Let us assume you have already successfully built Proto Go to the base directory and type proto n 1000 r 10 1 c T v red gradient once lt rnd O 1 0 01 You should see a green network with blue unreadable text at the intersections Red dots will spread through the screen from several starting locations as a magenta number in the lower left counts upward Drag with your left mouse button to rotate the display You will see that the red dots form a mountainous landscape Drag with your right mouse button to zoom and get a better view Let s break down this command n 1000 means use 1000 devices and r 10 means connect devices within 10 meters of one another The c means show the network it s the green thing hit c to turn it off You ll notice the magenta number in the lower right go up when you do that it s displaying how many frames per second the simulator is rendering and the one in the lower left is displaying the number of simulated seconds that have elapsed The timing display was invoked by T hit T shift t to turn them off Now you are looking at just the blue numbers and the red dots and it s time to delve into the Proto expression a little it s the big thing inside the quotes The expression rnd 0 1 means that all 1000 devices should pick random floating point numbers between 0 and 1 The comparison lt rnd 0 1 0 01 turns t
8. lues a local is anything but a field and a boolean is a scalar interpreted as a logical value false is 0 anything else is true Namespaces and Bindings Proto is a lexically scoped language Names are not case sensitive Bindings contain values and are looked up by name Lexical bindings are visible only within the scope in which they are bound and shadow bindings of the same name from enclosing scopes When the Proto compiler encounters an unknown identifier name it searches its path for a file named name proto If it finds such a file then it loads the contents of the file and looks up the identifier again Definitions in subdirectories can be accessed with identifiers of the form dir name def name arg body Define a function name in the current scope with as many arguments as there are arg identifiers The body is evaluated within an extended scope where the arg identifiers are bound to arguments to the function fun which omits name creates anonymous functions let var value body Extends scope binding all var identifiers to their asso ciated value in parallel The body is evaluated in the extended scope let is like let except that identifies are bound sequentially so later ones can use earlier ones in their definition Control Flow all forms All forms are evaluated in parallel and the value of the last form returned mux test true false Evaluates both true and false expressions When test
9. tements Capable of violating the continuous space time abstraction rep var init evolve Create a single feedback variable and return its value Equivalent to letfed var init evolve var Capable of violating the continuous space time abstraction once expr Evaluates expr once then always returns that value Logic and Arithmetic e Logical operators and or not Constants inf e pi Arithmetic neg negation e Comparison lt gt lt gt Functions pow min max sqrt abs sin cos atan2 e Random Numbers rnd min max gives a floating point random number in the range min mag Vectors vdot a b normalize v polar to rect v rect to polar v Tuples tuple v Creates a tuple with the set of v arguments as its elements elt tuple i Returns the ith element of tuple counting from zero 1st 2nd and 3rd are functions for getting elements 0 1 and 2 Neighborhoods There are two types of neighborhood functions functions that create fields and functions that summarize fields into local values In between any pointwise function can be applied to fields producing a field whose values are the result of applying the pointwise operation to the values of the input fields e nbr expr Returns a field mapping neighbors to their values of expr e nbr range nbr angle nbr lag nbr vec return a field of distances bearings time lags and ve
10. y in the directory lib distance to source Calculates the shortest path distance from every device to the set of devices where source is true The function gradient is an alias broadcast source value Flow value outward from devices in the source to all other devices Each device takes its value from the nearest source device dilate source d Returns true for every device within distance d of the source distance regionl region2 Calculates the distance between region1 and region2 and broadcasts it everywhere disperse Devices repel from one another using spring forces dither Devices wander randomly in a 2D plane elect Devices choose a leader by mutual exclusion and maintain precisely one leader within a given distance timer Return the length that this device has been evaluating this expression i e not going in different branches of an if 4 Simulator Essentials Key q Quit the simulator Argument v Key n Show value computed at each device Toggled by key Argument sv Key v When device outputs a 2 or 3 tuple display it as a vector toggled by key Argument T Key T Display simulator time in lower left corner and frames per second in lower right corner Toggled by key Argument step Key s Use stepping mode advancing one step on key s Key x Execute freely ending stepping mode Argument s N Set simulated seconds per step default 0 01 ratio Display Argum
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