ParaFlow

1
ParaFlow

• A practical, easy to use, parallel processing
  language.

2
Parallel programming constructs

• Para executes in parallel on all items in a
  collection.
• Flow marks a function as having no side effects.

3
Simplicity

• No objects or even functions are required. Hello
  world program is just
• print(Hello world.)
• Built in string type is easy and powerful.
• Memory for strings and objects is automatically
  freed. Files are automatically closed.
• Syntax is simple and readable. Generally very
  like C or Java.
• No threads to synchronize.

4
Example Flow Function

• flow polar(double angle,rad) into (double x,y)
• x rad math.cos(angle)
• y rad math.sin(angle)
• (double a,r) polar(4.0, 5.0)
• // The compiler would report an error if
• // the polar function modified any
• // global variables since it is declared as
• // flow. Functions with side effects must be
• // declared with the to keyword instead.

5
Para expression constructs

• // Make an array to work on.
• array of int a (1,2,3,4,5,6)
• // Get array of all elements squared
• array of int aSquared para (x in a) get xx
• // Get maximum value in array
• int maxA para (x in a) max x
• // Get array just containing odd numbers
• array of int odd para (x in a) filter x1

6
The parado construct

• // Declare a 2-D point class
• class point double x,y
• // function to scale an array of points
• to blowUp(array of point points, double
  scaleFactor)
• // With the para do construct can alter
• // all elements in a collection in parallel.
• para (p in points) do
• p.x scaleFactor
• p.y scaleFactor

7
The case statement

• // The case is different from Cs switch
• case (name)
• Mark,Angie occupation programmer
• Heidi occupation writer
• Rover
• occupation dog
• print(Woof)
• else occupation unknown
• // Motivation for difference is to avoid problems
  
• // with missing breaks, and allow use of
  non-integer
• // expressions.

8
Object Oriented Features

• Classes with single inheritance.
• Interfaces similar to Java. Automatic
  serialization of objects
• No overloading (but default parameters allowed).
• Methods must be declared polymorphic to be
  overridden.

9
A Simple Class and Serialization

• class family
• string name
• array of string members
• family kents (Kent, (Mira, Tisa, Jim,
  Heidi))
• print(kents)
• gt (Kent, (Mira, Tisa, Jim, Heidi))
• print(kents.members.size)
• gt 4

10
Other Advanced Features

• Flexible quotes makes embedding HTML and other
  intricate text in program easy.
• Does variable substitution in strings.
• Bounds checking on array accesses, and checking
  for use of uninitialized objects. Errors generate
  stack trace and position of error in source.
• For statement operates over collections (and
  makes bounds checks unneeded). Traditional for
  () also supported.
• No need to predeclare functions or for separate
  header files.
• Built in dir (aka hash,directory) collection. No
  need to cast objects out of collections.

11
Printing HTML fragment

• string title My ParaFlow CGI Program
  programName
• string background images/gears.jpg
• print(quote to ENDOFHTML
• ltHTMLgt
• ltHEADgtltTITLEgttitlelt/TITLEgtlt/HEADgt
• ltBODYgt BACKGROUNDbackgroundgt
• ltPgtHello HTML CGI World from ParaFlowlt/Pgt
• lt/BODYgt
• lt/HTMLgt
• ENDOFHTML)

12
Example Dir and For

• dir of int numNames
• (one _at_ 1, two _at_ 2, three _at_ 3)
• print(numNamesone)
• 1
• for (i in numNames)
• print( i ii)
• 1 1
• 2 4
• 3 9
• for (key_at_val in numNames)
• print(key -gt val)
• one -gt 1
• two -gt 2
• three-gt 3

13
Run Time Errors

• to goTooFar(array of int a, int value)
• // Set all elements of a to a value with a bug
• for (int i0 ilt a.size i)
• ai value
• to initArrays(array of int a, int aVal, string
  why)
• // Initialize two arrays to values
• print(Initializing a and b because why)
• goTooFar(a,aVal)
• array10 of int a
• initArrays(a,123,just because)
• Initializing a because just because
• -------- start stack dump --------
• goTooFar(altarray of 10gt, value123)
• initArrays(altarray of 10gt, aVal123, whyjust
  because)
• Run time error line 5 col 4 of pastEnd.pf array
  access out of bounds

14
More complex classes

• class animal
• string name
• to printName() print(self.name)
• polymorphic to speak() print(???)
• class dog extends animal
• polymorphic to speak() print(bark)
• class toyPoodle extends dog
• polymorphic to speak() print(yip)
• dog fido (Fido), toyPoodle fifi (Fifi)
• array of animals (fido, fifi)
• foreach (a in animals)
• a.speak()
• gtbark

15
Whats Implemented

• Classes with inheritance polymorphism
• Print and file I/O that handles objects of
  different types without being told how.
• For, while, if, case, functions with multiple
  returns
• Modules, exceptions, interfaces
• String, file, html fetch libraries.
• Reference counting/auto freeing of objects
• Serial implementations of para constructs.

16
Still to come

• Making parallel constructs actually work in
  parallel.
• Generating Pentium rather than C code.
• Current code is about 1/4 speed of equivalent C
• Generating Open Source buzz on language
• Open Source Conf Portland in July is launch

17
Implementation

• Whole module done in memory in many passes
• Tokenizer
• Scan tokens for class names
• Parser
• Resolving variable names
• Type checker
• C code generator
• Calls gcc on C code.