Template Haskell allows code to be generated at compile time by splicing quasi quotations into the abstract syntax tree. It works by running Haskell code that constructs syntax expressions and splicing the results into the code being compiled. This allows features like generating boilerplate code, domain-specific languages, and compile-time metaprogramming in Haskell.

1. Template Haskell
konn

2. Template Haskell

3. Template Haskell
Haskell

4. Template Haskell
Haskell

5. Template Haskell
Haskell
Q

6. Template Haskell
Haskell
Q
C preprocessor

7. TH

8. TH
Haskell

9. TH
Haskell
IO
compile-time wxWidgets Network...

11. RandomDef.hs
{-# LANGUAGE TemplateHaskell #-}
module Main where
import Language.Haskell.TH
import System.Random
$( do rnd <- runIO $ randomRIO (0,1)
let nm = mkName (["a", "b"] !! rnd)
m <- [d| main = $(varE $ mkName "a") |]
t <- valD (varP nm) (normalB [| putStrLn " ( ´ `) " |]) []
return (t:m)
)

12. RandomDef.hs
{-# LANGUAGE TemplateHaskell #-}
module Main where
import Language.Haskell.TH
import System.Random IO
$( do rnd <- runIO $ randomRIO (0,1)
let nm = mkName (["a", "b"] !! rnd)
m <- [d| main = $(varE $ mkName "a") |]
t <- valD (varP nm) (normalB [| putStrLn " ( ´ `) " |]) []
return (t:m)
)

13. Splice( )
{-# LANGUAGE TemplateHaskell #-}
module Main where
import Language.Haskell.TH
import System.Random
$( do rnd <- runIO $ randomRIO (0,1)
let nm = mkName (["a", "b"] !! rnd)
m <- [d| main = $(varE $ mkName "a") |]
t <- valD (varP nm) (normalB [| putStrLn " ( ´ `) " |]) []
return (t:m)
)

14. Splice

15. Splice
(Q )

16. Splice
(Q )
splice
splice

17. Splice
(Q )
splice
splice
“ ”

18. {-# LANGUAGE TemplateHaskell #-}
module Main where
import Language.Haskell.TH
import System.Random
$( do rnd <- runIO $ randomRIO (0,1)
let nm = mkName (["a", "b"] !! rnd)
m <- [d| main = $(varE $ mkName "a") |]
t <- valD (varP nm) (normalB [| putStrLn " ( ´ `) " |]) []
return (t:m)
)

20. [ |

21. [ |
[| putStrLn “hogehoge” |]

22. [ |
[| putStrLn “hogehoge” |]
[t| String |]

23. [ |
[| putStrLn “hogehoge” |]
[t| String |]
[d| main = putStrLn |]

24. [ |
[| putStrLn “hogehoge” |]
[t| String |]
[d| main = putStrLn |]
[$ident| function f() {..} |]

25. [ |
[| putStrLn “hogehoge” |]
[t| String |]
[d| main = putStrLn |]
[$ident| function f() {..} |]
DSL

26. [ |
[| putStrLn “hogehoge” |]
[t| String |]
[d| main = putStrLn |]
[$ident| function f() {..} |]
DSL

27. [ |
[| putStrLn “hogehoge” |]
[t| String |]
[d| main = putStrLn |]
[$ident| function f() {..} |]
DSL
)JavaScript (

28. splice
[d| main = $(varE $ mkName "a") |]
splice
[d| main = ‘a |] TH
a
`a
``String

29. {-# LANGUAGE TemplateHaskell #-}
module Main where
import Language.Haskell.TH
import System.Random
$( do rnd <- runIO $ randomRIO (0,1)
let nm = mkName (["a", "b"] !! rnd)
m <- [d| main = $(varE $ mkName "a") |]
t <- valD (varP nm) (normalB [| putStrLn " ( ´ `) " |]) []
return (t:m)
)

30. valD (varP nm) (normalB [| putStrLn " ( ´ `) " |]) []
[d| $(varP nm) = putStrLn “ ( ´ `) ” |]
…… ……
ghci
> runQ [d| main = putStrLn “hoge” |]

31. Sucks
GHC
TH Ver.UP
(ex. HOC )

32. lib2 =
let
l=LetS[ValD(VarP $ mkName"it")(NormalB(f"be"))[]]
f=VarE . mkName
in
DoE [ l, l, l, NoBindS $ f"oh",l,
NoBindS $ InfixE(Just$ f"speaking")(f"words")(Just $ f "wisdom"),l]

33. lib2 =
let
l=LetS[ValD(VarP $ mkName"it")(NormalB(f"be"))[]]
f=VarE . mkName
in
DoE [ l, l, l, NoBindS $ f"oh",l,
NoBindS $ InfixE(Just$ f"speaking")(f"words")(Just $ f "wisdom"),l]

34. lib2 =
let
l=LetS[ValD(VarP $ mkName"it")(NormalB(f"be"))[]]
f=VarE . mkName
in
DoE [ l, l, l, NoBindS $ f"oh",l,
NoBindS $ InfixE(Just$ f"speaking")(f"words")(Just $ f "wisdom"),l]
do let it = be
let it = be
let it = be
oh
let it = be
speaking `words` wisdom
let it = be

35. reify
IO reify
Q