Project Fortress

Project Fortress
Alex Miller

http://www.ﬂickr.com/photos/micbaun/1216608114/
Wednesday, July 1, 2009

Dude, isn’t
Fortress like
FORTRAN or
something?

http://www.ﬂickr.com/photos/ﬁnkle/3111290180/

Um, no.


Modern language design

+

Scientiﬁc computing


Features of interest
Mathematical rendering
Parallelism
Software transactional memory
Operator and function overloading
Objects / traits
Contracts
Components / apis


Let’s build some basics


Types

ZZ32, ZZ64 - signed integer types
RR32, RR64 - ﬂoating point types

String
Boolean


juxtaposition

3 4 evaluates to 12
“a” “b” evaluates to “ab”

log 1 evaluates to 0


Ranges

5:9 evaluates to [5,6,7,8,9]
5:9:2 evaluates to [5,7,9]

5#2 evaluates to [5,6]


Variables
Immutable: name[:type] = value
zero = 0
zero:ZZ32 = 0
Mutable: var name[:type] = value
OR name[:type] := value
var sum = 0
sum := 0


Now you’re dangerous.


A simple example
component fact
export Executable

fact(n:ZZ32): ZZ32 =
if n = 0 then 1
else n fact(n-1)
end

run():()=do
for k<-seq(1:10) do
println " fact(" k ") = " fact(k)
end
end

end

Executable - a trait juxtaposition as operator
deﬁning run()
Parallelism - in terms, in for
Rendering: ZZ32, <-, fonts
seq() - force sequential


BIG ideas

But factorial is just a big multiply...use aggregate PROD
operator ∏ instead.
This is known as a BIG operator.


More direct implementation
component factp
export Executable

factp(n:ZZ32): ZZ32 =
PROD [i <- 1:n] i

run():()=do
for k<-seq(1:10) do
println " factp(" k ") = " factp(k)
end
end

end

PROD = aggregate Known as “BIG”
product operators
SUM = summation You can make your own!

Operator overloading

Would be nice to actually use the right mathematical
operator ! instead of a function, wouldn’t it?


Let’s make it an operator
component facto
export Executable

opr(n:ZZ32)! = PROD [i <- 1:n] i

run():()=do
for k<-seq(1:10) do
println k "! = " k!
end
end

end

opr() used to define a Also can do prefix, infix,
postfix operator here nofix, multifix, or
enclosing!


Lists
evens = <|[ZZ32] 2,4,6,8,10|>
println "evens: " evens

evens2 = <|[ZZ32] 2 x | x <- 1:5|>
println "evens2: " evens2

odds = <|[ZZ32] e - 1 | e <- evens |>
println "odds: " odds

evens: <|2, 4, 6, 8, 10|>
evens2: <|2, 4, 6, 8, 10|>
odds: <|1, 3, 5, 7, 9|>


Another example
component sos
import List.{...}
export Executable

sumOfSquares(n:List[ZZ32]): ZZ64 = do
sum:ZZ64 := 0
for i<-0#|n| do
sum += (n[i])^2
end
sum
end

run():()=do
theList = <|[ZZ32] x | x<-1#100|>
println "sumOfSquares = "
sumOfSquares(theList)
end

end

What’s the bug? (Hint: think parallelism)


Implicit parallelism
Many things implicitly parallel
for loops
parameters to a function call
do ... also ... end construct
Here, for loop is parallel, so sum += is a data race
Use atomic to ﬁx


Atomic punk
component sos
import List.{...} Fortress uses Software
export Executable
Transactional Memory
sumOfSquares(n:List[ZZ32]): ZZ64 = do

atomic blocks executed all
sum:ZZ64 := 0
for i<-0#|n| do

or nothing
atomic sum += (n[i])^2
end
sum

Retry on collision
end

run():()=do
theList = <|[ZZ32] x | x<-1#100|>
println "sumOfSquares = " Transactions may nest
sumOfSquares(theList)
end
tryatomic
end


Traits
component traitexample
export Executable
trait - like Java interface
trait Animal
talk():String
end methods - abstract or
trait Fuzzy concrete
howFuzzy():String
end
object - like Java ﬁnal class
trait Cat extends Animal

ﬁelds, methods
getter name():String
talk() = "meow"
end

object Whiskers extends {Cat, Fuzzy} constructors
name() = "Whiskers"
howFuzzy() = "real fuzzy"
end multiple inheritance
run():() = do
w:Whiskers = Whiskers getter / setter - metadata
println w.name() " is " w.howFuzzy()
end
end

Function contracts
component factc
export Executable Documentation of
factorial(n:ZZ32):ZZ32 semantic constraints
requires { n >= 0 }
ensures { outcome >= 0 } beyond the type system.
= PROD [i <- 1:n] i

run():() = do requires - speciﬁes pre-
conditions on incoming
for k<-seq(1:10) do
println k "! = " factorial(k)

arguments
end
end
end

ensures - speciﬁes post-
condition on “outcome”


Components and APIs

Components modularize your program
Components export and import APIs (NEVER other
components, just APIs)
APIs are explicitly deﬁned in their own ﬁle type
Repository for components


And more...
Literal arrays, multi-dimensional arrays
Maps, sets, skip lists, trees, heaps, sparse vectors and matrices,
quick sort, etc in library
Explicit thread spawn, memory region tree
Function overloading
Tuples
Tests
Functions as ﬁrst class objects
Exceptions


Whither next?

Currently working on compiler
Goal is to have it working in 6 months for a real
bioinformatics project


For more...

Project Home: http://projectfortress.sun.com/Projects/
Community
David Chase: http://www.infoq.com/presentations/
chase-fortress
Guy Steele, Eric Allen: http://tinyurl.com/md6f6g


Alex Miller

Twitter: http://twitter.com/puredanger
Blog: http://tech.puredanger.com
Presentations: http://slideshare.net/alexmiller


Project Fortress

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