Foreign Inline Code in Haskell Manuel M T Chakravarty University of - - PowerPoint PPT Presentation

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Foreign Inline Code in Haskell Manuel M T Chakravarty University of - - PowerPoint PPT Presentation

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Foreign Inline Code in Haskell Manuel M T Chakravarty University of New South Wales mchakravarty TacticalGrace TacticalGrace justtesting.org 1 30 minute time slot: 25min talking + 5min [15min The Problem; 5min TH+Quasiquoting; 5min

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Manuel M T Chakravarty University of New South Wales

Foreign Inline Code in Haskell

mchakravarty

α

TacticalGrace TacticalGrace justtesting.org

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30 minute time slot: 25min talking + 5min [15min The Problem; 5min TH+Quasiquoting; 5min Inline Objective-C]

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λ

Shiny new functional language

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» Imagine, you have got a shiny, new functional language...

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» ...and you want to use it to write a great new app...

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λ

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» ...then you will need to use many existing frameworks and libraries. » Luckily, any serious language will have a foreign function interface! » Haskell standard includes a simple, but versatile FFI

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“Problem solved?”

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» Does that solve the problem of language interoperability? » Let me explain that at an example...

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“Problem solved?”

N

  • !

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» Does that solve the problem of language interoperability? » Let me explain that at an example...

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dumpURL :: String -> IO () dumpURL urlString = do urlData <- stringWithContentsOfUrl urlString putStr urlData

What we want to write

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dumpURL :: String -> IO () dumpURL urlString = do urlData <- stringWithContentsOfUrl urlString putStr urlData

What we want to write

char *stringWithContentsOfUrlCstub(char *urlString) { NSURL *url = [NSURL URLWithString:urlString]; [NSString stringWithContentsOfURL:url

encoding:NSUTF8StringEncoding error:NULL];

}

What we want to call (& need to put into an extra file)

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What we have to write as well…

foreign import stringWithContentsOfURLCstub :: CString -> IO CString stringWithContentsOfURL :: String -> IO String stringWithContentsOfURL url = withCString url $ \urlC -> do resultC <- stringWithContentsOfURLCstub urlC result <- peek resultC free resultC return result

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» FFI code: If you find it confusing, that’s fine, as I want to argue that you shouldn’t write it in the first place. * Anything extensively relying on foreign frameworks will be a pain [Hybrid languages (eg, F# & Scala) have a difgerent set of trade ofgs, but don’t solve it either.]

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Bridging Libraries

1-to-1 transliteration of types & functions

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* Bridging or binding libraries transliterate types & functions * Need to be maintained and documented; track multiple versions of base library * Lack of type safety * Tools and dynamic transliteration (by reflection) help

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C➙Haskell

c2hs

A case study

GTK+

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* c2hs: automation for bridging C libraries to Haskell <https://hackage.haskell.org/package/ c2hs> * Implements large parts of a C compiler front-end * Bridge for the cross-platform Gnome GUI library GTK+ <http://projects.haskell.org/ gtk2hs/>

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* AFAIK, currently the only fully featured and properly maintained Haskell GUI library * Haskell GTK+ library is used for realistic applications

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“Does this approach scale?”

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» Read question * It requires significant resources & constant efgort to track the original library * Application frameworks: enormous and growing footprint

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February 2011 Introduction of GTK+ 3

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* Base GTK+ development isn’t even particularly fast * Bridging libraries lag behind their base libraries * Another example: Haskell OpenGL library

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February 2011 Introduction of GTK+ 3 December 2013 GTK+ 3 in Haskell Bridge

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* Base GTK+ development isn’t even particularly fast * Bridging libraries lag behind their base libraries * Another example: Haskell OpenGL library

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* Compared to modern application frameworks, GTK+ is small!

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Bridging libraries don’t scale

Too much weight!

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“Interoperability is an old problem — maybe an old solution can help?”

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* Modula-2 with inline 68000 assembly * Assembly code can symbolically refer to Modula-2 entities (e.g., variables)

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* Modula-2 with inline 68000 assembly * Assembly code can symbolically refer to Modula-2 entities (e.g., variables)

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* Modula-2 with inline 68000 assembly * Assembly code can symbolically refer to Modula-2 entities (e.g., variables)

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“Inline C, C++, Objective-C, … in Haskell?”

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* We don’t want to build front ends for a few more languages into GHC * How do we share entities between the languages?

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Meta-programming Template Haskell

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» Generic infrastructure for program manipulation NOTE: I'll run through this quickly; I'll explain the details at the workshop.

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HASKELL WORKSHOP 2002

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* Template Haskell: Haskell extension implemented by GHC * Useful for: defining macros, code generators, code transformations… * Other languages have their own variants; eg., MetaOCaml » Let’s look at an example…

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HASKELL WORKSHOP 2002

#define

macros

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* Template Haskell: Haskell extension implemented by GHC * Useful for: defining macros, code generators, code transformations… * Other languages have their own variants; eg., MetaOCaml » Let’s look at an example…

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HASKELL WORKSHOP 2002

#define

macros

[| … |]

code generators

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* Template Haskell: Haskell extension implemented by GHC * Useful for: defining macros, code generators, code transformations… * Other languages have their own variants; eg., MetaOCaml » Let’s look at an example…

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HASKELL WORKSHOP 2002

#define

macros

[| … |]

code generators

trafo (ConE name) = …

code transformations

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* Template Haskell: Haskell extension implemented by GHC * Useful for: defining macros, code generators, code transformations… * Other languages have their own variants; eg., MetaOCaml » Let’s look at an example…

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$(sel 1 3) (a, b, c) = a

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* Meta function executed at splice point, generating spliced code

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$(sel 1 3) (a, b, c) = a

meta-programming function

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* Meta function executed at splice point, generating spliced code

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$(sel 1 3) (a, b, c) = a

meta-programming function splice

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* Meta function executed at splice point, generating spliced code

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$(sel 1 3) (a, b, c) = a

meta-programming function splice

\tup -> case tup of {(x, y, z) -> x} :: (a, b, c) -> a

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* Meta function executed at splice point, generating spliced code

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$(sel 1 3) (a, b, c) = a

meta-programming function splice

\tup -> case tup of {(x, y, z) -> x} :: (a, b, c) -> a $(sel 5 5) (a, b, c, d, e) = e

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* Meta function executed at splice point, generating spliced code

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$(sel 1 3) (a, b, c) = a

meta-programming function splice

\tup -> case tup of {(x, y, z) -> x} :: (a, b, c) -> a $(sel 5 5) (a, b, c, d, e) = e \tup -> case tup of {(x, y, z, v, w) -> w} :: (a, b, c, d, e) -> e

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* Meta function executed at splice point, generating spliced code

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sel :: Int -> Int -> ExpQ sel i n = [| \tup -> case tup of {$pat -> $res} |] where pat = tupP (map varP names) res = varE (names !! (i - 1)) names = [mkName $ "v" ++ show i | i <- [1..n]]

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* Quasiquotations in [|..|] brackets * Explain TH in more detail in the workshop

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sel :: Int -> Int -> ExpQ sel i n = [| \tup -> case tup of {$pat -> $res} |] where pat = tupP (map varP names) res = varE (names !! (i - 1)) names = [mkName $ "v" ++ show i | i <- [1..n]]

type of Haskell expressions

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* Quasiquotations in [|..|] brackets * Explain TH in more detail in the workshop

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sel :: Int -> Int -> ExpQ sel i n = [| \tup -> case tup of {$pat -> $res} |] where pat = tupP (map varP names) res = varE (names !! (i - 1)) names = [mkName $ "v" ++ show i | i <- [1..n]]

type of Haskell expressions quasi-quotation

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* Quasiquotations in [|..|] brackets * Explain TH in more detail in the workshop

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sel :: Int -> Int -> ExpQ sel i n = [| \tup -> case tup of {$pat -> $res} |] where pat = tupP (map varP names) res = varE (names !! (i - 1)) names = [mkName $ "v" ++ show i | i <- [1..n]]

type of Haskell expressions quasi-quotation spliced expression (anti quote)

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* Quasiquotations in [|..|] brackets * Explain TH in more detail in the workshop

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Processing other languages Generic quasi-quotation

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* Quoting arbitrary languages

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HASKELL WORKSHOP 2007

Quasiquoting for any language you can provide a parser for

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Language.C.Quote

add n = [cfun| int addConstant(int x) { return x + $int:n; } |]

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* QQ for C including some GNU extensions, parts of CUDA & OpenCL, and all of Objective-C

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Language.C.Quote

add n = [cfun| int addConstant(int x) { return x + $int:n; } |]

quasi-quotation identifier

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* QQ for C including some GNU extensions, parts of CUDA & OpenCL, and all of Objective-C

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Language.C.Quote

add n = [cfun| int addConstant(int x) { return x + $int:n; } |]

quasi-quotation identifier splice identifier

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* QQ for C including some GNU extensions, parts of CUDA & OpenCL, and all of Objective-C

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mkMap dev aenv fun arr = return $ CUTranslSkel "map" [cunit| $esc:("#include <accelerate_cuda.h>") extern "C" __global__ void map ($params:argIn, $params:argOut) { const int shapeSize = size(shOut); const int gridSize = $exp:(gridSize dev); int ix; for ( ix = $exp:(threadIdx dev) ; ix < shapeSize ; ix += gridSize ) { $items:(dce x .=. get ix) $items:(setOut "ix" .=. f x) } } |] where ...

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* Accelerate: embedded high-performance array language for GPUs * Combinators as code skeletons (code templates with holes) * Yellow splices/anti-quotes are the holes (parameters) of the template * Doing this with strings or explicit AST construction would be much worse

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mkMap dev aenv fun arr = return $ CUTranslSkel "map" [cunit| $esc:("#include <accelerate_cuda.h>") extern "C" __global__ void map ($params:argIn, $params:argOut) { const int shapeSize = size(shOut); const int gridSize = $exp:(gridSize dev); int ix; for ( ix = $exp:(threadIdx dev) ; ix < shapeSize ; ix += gridSize ) { $items:(dce x .=. get ix) $items:(setOut "ix" .=. f x) } } |] where ...

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* Accelerate: embedded high-performance array language for GPUs * Combinators as code skeletons (code templates with holes) * Yellow splices/anti-quotes are the holes (parameters) of the template * Doing this with strings or explicit AST construction would be much worse

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mkMap dev aenv fun arr = return $ CUTranslSkel "map" [cunit| $esc:("#include <accelerate_cuda.h>") extern "C" __global__ void map ($params:argIn, $params:argOut) { const int shapeSize = size(shOut); const int gridSize = $exp:(gridSize dev); int ix; for ( ix = $exp:(threadIdx dev) ; ix < shapeSize ; ix += gridSize ) { $items:(dce x .=. get ix) $items:(setOut "ix" .=. f x) } } |] where ...

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* Accelerate: embedded high-performance array language for GPUs * Combinators as code skeletons (code templates with holes) * Yellow splices/anti-quotes are the holes (parameters) of the template * Doing this with strings or explicit AST construction would be much worse

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Inlining foreign languages Inline C Code

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Language.C.Inline

dumpURL :: String -> IO () dumpURL urlString = do urlData <- putStr urlData stringWithContentsOfUrl urlString

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* Inline Objective-C * All the FFI code is generated automatically * Again, details in the workshop

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Language.C.Inline

dumpURL :: String -> IO () dumpURL urlString = do urlData <- putStr urlData

$(objc ['urlString] ''String [cexp| [NSString stringWithContentsOfURL: [NSURL URLWithString:urlString] encoding:NSUTF8StringEncoding error:NULL] |])

inline Objective-C splice

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* Inline Objective-C * All the FFI code is generated automatically * Again, details in the workshop

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Inline C

…is simple

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* Lack of bridge saves a lot of work; instant access to new versions * Bridges require familiarity with native libraries already; inline code leverages that directly * Haskell types are automatically mapped to types of the inline language

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Inline C

…is simple

No bridging library needs to be maintained

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* Lack of bridge saves a lot of work; instant access to new versions * Bridges require familiarity with native libraries already; inline code leverages that directly * Haskell types are automatically mapped to types of the inline language

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Inline C

…is simple

No extra documentation

No bridging library needs to be maintained

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* Lack of bridge saves a lot of work; instant access to new versions * Bridges require familiarity with native libraries already; inline code leverages that directly * Haskell types are automatically mapped to types of the inline language

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Inline C

…is simple

No extra documentation Some type safety

No bridging library needs to be maintained

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* Lack of bridge saves a lot of work; instant access to new versions * Bridges require familiarity with native libraries already; inline code leverages that directly * Haskell types are automatically mapped to types of the inline language

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Language integration by language inlining

types >< state languages

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Outline workshop * Get familiar with TH and Language.C.Quote * Run through three exercises using inline Objective-C including a graphical REPL

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Workshop Part 1 Template Haskell

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* http://www.haskell.org/haskellwiki/Template_Haskell * http://hackage.haskell.org/package/template-haskell

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Clone https://github.com/mchakravarty/ylj14-workshop

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printf :: String -> ExpQ printf fmt = gen (parse fmt)

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printf :: String -> ExpQ printf fmt = gen (parse fmt) data Format = D | S | L String parse :: String -> [Format]

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printf :: String -> ExpQ printf fmt = gen (parse fmt) data Format = D | S | L String parse :: String -> [Format] gen :: [Format] -> ExpQ gen [D] = [| \n -> show n |] gen [S] = [| \s -> s |] gen [L s] = [| s |]

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Task ❶

A recursive generator

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printf/

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printf :: String -> ExpQ printf fmt = gen (parse fmt) [| "" |]

printf/

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printf :: String -> ExpQ printf fmt = gen (parse fmt) [| "" |] gen :: [Format] -> ExpQ -> ExpQ

printf/

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printf :: String -> ExpQ printf fmt = gen (parse fmt) [| "" |] gen :: [Format] -> ExpQ -> ExpQ gen [] prefix = prefix

printf/

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printf :: String -> ExpQ printf fmt = gen (parse fmt) [| "" |] gen :: [Format] -> ExpQ -> ExpQ gen [] prefix = prefix gen (D : fmt) prefix

printf/

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printf :: String -> ExpQ printf fmt = gen (parse fmt) [| "" |] gen :: [Format] -> ExpQ -> ExpQ gen [] prefix = prefix gen (D : fmt) prefix = [| \n -> $(gen fmt [| $prefix ++ show n |]) |]

printf/

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printf :: String -> ExpQ printf fmt = gen (parse fmt) [| "" |] gen :: [Format] -> ExpQ -> ExpQ gen [] prefix = prefix gen (D : fmt) prefix = [| \n -> $(gen fmt [| $prefix ++ show n |]) |] gen (S : fmt) prefix

printf/

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printf :: String -> ExpQ printf fmt = gen (parse fmt) [| "" |] gen :: [Format] -> ExpQ -> ExpQ gen [] prefix = prefix gen (D : fmt) prefix = [| \n -> $(gen fmt [| $prefix ++ show n |]) |] gen (S : fmt) prefix = [| \s -> $(gen fmt [| $prefix ++ s |]) |]

printf/

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printf :: String -> ExpQ printf fmt = gen (parse fmt) [| "" |] gen :: [Format] -> ExpQ -> ExpQ gen [] prefix = prefix gen (D : fmt) prefix = [| \n -> $(gen fmt [| $prefix ++ show n |]) |] gen (S : fmt) prefix = [| \s -> $(gen fmt [| $prefix ++ s |]) |] gen (L s : fmt) prefix

printf/

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printf :: String -> ExpQ printf fmt = gen (parse fmt) [| "" |] gen :: [Format] -> ExpQ -> ExpQ gen [] prefix = prefix gen (D : fmt) prefix = [| \n -> $(gen fmt [| $prefix ++ show n |]) |] gen (S : fmt) prefix = [| \s -> $(gen fmt [| $prefix ++ s |]) |] gen (L s : fmt) prefix = gen fmt [| $prefix ++ s |]

printf/

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Workshop Part 2 Quasi-quotation of C variants

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* http://hackage.haskell.org/package/language-c-quote

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gensum/

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genSum :: Name -> Int -> BlockItem genSum arr n = [citem| { int sum = 0; for (int i = 0; i++; i < $n) sum += $id:(show arr)[i]; } |]

gensum/

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genSum :: Name -> Int -> BlockItem genSum arr n = [citem| { int sum = 0; for (int i = 0; i++; i < $n) sum += $id:(show arr)[i]; } |]

custom parser for C block items gensum/

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genSum :: Name -> Int -> BlockItem genSum arr n = [citem| { int sum = 0; for (int i = 0; i++; i < $n) sum += $id:(show arr)[i]; } |]

custom parser for C block items splicing of a name as an identifier gensum/

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genSum :: Name -> Int -> BlockItem genSum arr n = [citem| { int sum = 0; for (int i = 0; i++; i < $n) sum += $id:(show arr)[i]; } |]

custom parser for C block items splicing of a name as an identifier default is to splice as an expression gensum/

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Task ❷

Loop unrolling

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Replace the for loop by a statement sequence

[cstms| … |]

quote a statement sequence

$stms:…

splice a statement sequence

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genSum arr n = [citem| { int sum = 0; $stms:(additions 0) } |] where additions i | i == n = [] | otherwise = [cstms| sum += $id:(show arr)[ $int:i ]; $stms:(additions (i + 1)) |]

Replace the for loop by a statement sequence

[cstms| … |]

quote a statement sequence

$stms:…

splice a statement sequence

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Workshop Part 3 Inline Objective-C Code

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* http://hackage.haskell.org/package/language-c-inline

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{-# LANGUAGE TemplateHaskell, QuasiQuotes #-} import Language.C.Quote.ObjC import Language.C.Inline.ObjC

  • bjc_import ["<Foundation/Foundation.h>"]

nslog :: String -> IO () nslog msg = $(objc ['msg] ''() [cexp| NSLog(@"Here is a message from Haskell: %@”, ! ! ! ! ! ! msg) |])

  • bjc_emit

minimal/

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* Complete the skeleton in the exercise pack

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{-# LANGUAGE TemplateHaskell, QuasiQuotes #-} import Language.C.Quote.ObjC import Language.C.Inline.ObjC

  • bjc_import ["<Foundation/Foundation.h>"]

nslog :: String -> IO () nslog msg = $(objc ['msg] ''() [cexp| NSLog(@"Here is a message from Haskell: %@”, ! ! ! ! ! ! msg) |])

  • bjc_emit

imports for the generated Objective-C code minimal/

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* Complete the skeleton in the exercise pack

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{-# LANGUAGE TemplateHaskell, QuasiQuotes #-} import Language.C.Quote.ObjC import Language.C.Inline.ObjC

  • bjc_import ["<Foundation/Foundation.h>"]

nslog :: String -> IO () nslog msg = $(objc ['msg] ''() [cexp| NSLog(@"Here is a message from Haskell: %@”, ! ! ! ! ! ! msg) |])

  • bjc_emit

free variables imports for the generated Objective-C code minimal/

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* Complete the skeleton in the exercise pack

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{-# LANGUAGE TemplateHaskell, QuasiQuotes #-} import Language.C.Quote.ObjC import Language.C.Inline.ObjC

  • bjc_import ["<Foundation/Foundation.h>"]

nslog :: String -> IO () nslog msg = $(objc ['msg] ''() [cexp| NSLog(@"Here is a message from Haskell: %@”, ! ! ! ! ! ! msg) |])

  • bjc_emit

free variables imports for the generated Objective-C code finalise inline code minimal/

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* Complete the skeleton in the exercise pack

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Task ❸

Bridging classes

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particle/

Particle.hs

Represent Haskell record as ObjC class

Main.hs

Allocate instance and use it

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particle/

Particle.hs

Represent Haskell record as ObjC class

Main.hs

Allocate instance and use it

Complete the ObjC class implementation

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Task ❹

A simple application

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app/

Interpreter.hs

Haskell interface to package ghc

AppDelegate.hs

Haskell-Objective-C bridge

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app/

Interpreter.hs

Haskell interface to package ghc

AppDelegate.hs

Haskell-Objective-C bridge

Complete AppDelegate.hs

Run with open -a HSApp.app

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Thank you!

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Images from

http://wikimedia.org http://openclipart.org

GitHub repo

https://github.com/mchakravarty/language-c-inline

Megamax Modula-2 Screenshot by Dirk Steins