Write You a Haskell Stephen Diehl

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where f (Syn.EVar ”a”) = (Syn.EVar ”b”) f x = x is is good for pure logic, but most often our transformations will have to have access to some sort of state or context during traversal and thus the descedM will let us write the same rewrite but in a custom monadic context. transform :: Expr -> RewriteM Expr transform = descendM f where f (Syn.EVar x) = do env Expr) -> (Expr -> Expr) -> (Expr -> Expr) compose f g = descend (f . g) Recall from that monadic actions can be composed like functions using Kleisli composition operator. Functions : a -> b Monadic operations : a -> m b -- Function composition (.) :: (b -> c) -> (a -> b) -> a -> c f . g = \x -> g (f x) -- Monad composition ( m c) -> (a -> m b) -> a -> m c f g x >>= f We can now write composition descendM functions in terms of of Kleisli composition to give us a very general notion of AST rewrite composition. composeM :: (Applicative m, Monad m) => (Expr -> m Expr) -> (Expr -> m Expr) -> (Expr -> m Expr) composeM f g = descendM (f
So for instance if we have three AST monadic transformations (a, b, c) that we wish to compose into a single pass t we can use composeM to to generate the composite transformation. a :: Expr -> RewriteM Expr b :: Expr -> RewriteM Expr c :: Expr -> RewriteM Expr t :: Expr -> RewriteM Expr t = a ‘composeM‘ b ‘composeM‘ c Later we utilize both GHC.Generics and Uniplate to generalize this technique even more. Full Source e partial source for the Frontend of Proto<strong>Haskell</strong> is given. is is a stub of the all the data structure and scaffolding we will use to construct the compiler pipeline. • Proto<strong>Haskell</strong> Frontend e modules given are: • Monad.hs - Compiler monad • Flags.hs - Compiler flags • Frontend.hs - Frontend syntax • Name.hs - Syntax names • Compiler.hs - Initial compiler stub • Pretty.hs - Pretty printer • Type.hs - Type syntax Resources See: • e Architecture of Open Source Applications: GHC • GHC Commentary 127
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Write You a Haskell Building a mode
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Contents Introduction 6 Goals . . .
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Evaluation . . . . . . . . . . . .
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Syntax Errors . . . . . . . . . . .
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• containers • unordered-contai
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File ””, line 1, in TypeError:
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] TokenSym ”x”, TokenAdd, Token
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f: mov res, arg add res, 1 ret defi
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Datatypes Constructors for datatype
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length :: [a] -> Int length [] = 0
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Higher-Kinded Types e “type of ty
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eturn a >>= f = f a Law 2 m >>= ret
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data PlatonicSolid = Tetrahedron |
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foo :: Stack () foo = Stack $ do pu
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, bar :: Int } deriving (Show) comp
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class IsString a where fromString :
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Parsing Parser Combinators For pars
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instance Monad Parser where return
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natural :: Parser Integer natural =
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print $ eval $ run a Now we can try
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module Syntax where data Expr = Tr
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cannot proceed because the reductio
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later into native CPU instructions
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λx.e ere are several syntactical c
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type Name = String data Expr = Var
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Eta-expansion (λx.ex)e ′ β →
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Y = SSK(S(K(SS(S(SSK))))K) In a unt
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parensIf :: Bool -> Doc -> Doc pare
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In this notation, the expression ab
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In all the languages which we will
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eval1 expr = case expr of Succ t ->
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TNat -> return TNat _ -> throwError
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• T-Var Variables are simply pull
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t1 throwError $ Mismatch t2 a ty -
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Full Source • Typed Arithmetic
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1. Evaluate f to λy.e 2. Evaluate
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e 1 → e ′ 1 e 1 e 2 → e ′ 1
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case we will use a GADT to embed a
Page 77 and 78: AppP (AppP (VarP f) (VarP x)) (AppP
Page 79 and 80: e prim function will simply perform
Page 81 and 82: ere is nothing more practical than
Page 83 and 84: As before let rec expressions will
Page 85 and 86: Γ, x : τ = (Γ\x) ∪ {x : τ} Op
Page 87 and 88: where s’ = foldr Map.delete s as
Page 89 and 90: s2 Type -> Infer Subst bind a t |
Page 91 and 92: infer :: TypeEnv -> Expr -> Infer (
Page 93 and 94: App e1 e2 -> do tv
Page 95 and 96: -- | Unify two types uni :: Type ->
Page 97 and 98: unifies t (TVar v) = v ‘bind‘ t
Page 99 and 100: Interpreter Our evaluator will oper
Page 101 and 102: Our language can be compiled into a
Page 103 and 104: exec True contents -- :type command
Page 105 and 106: let rec fib n = if (n == 0) then 0
Page 107 and 108: • Higher order functions • Para
Page 109 and 110: • e PHOAS, the type-erased Core i
Page 111 and 112: If the ProtoHaskell compiler is inv
Page 113 and 114: infixl 6 + infixl 7 * f = 1 + 2 * 3
Page 115 and 116: -- Desugared f x = case x of Just _
Page 117 and 118: data Kind = KStar | KArr Kind Kind
Page 119 and 120: TypeError) -- | Inference state dat
Page 121 and 122: e expression or Expr type is the co
Page 123 and 124: data qname [var] where [tydecl] dat
Page 125 and 126: Typeclass Declarations Typeclass de
Page 127: Syntax Name Kind Description (,) Pa
Page 131 and 132: -- **Begin Haskell Syntax** { {-# O
Page 133 and 134: tokens :- -- Whitespace insensitive
Page 135 and 136: Expr : let VAR ’=’ Expr in Expr
Page 137 and 138: data Type = TVar Loc TVar | TCon Lo
Page 139 and 140: -- Start of layout ( Column: 0 ) fi
Page 141 and 142: Extensible Operators Haskell famous
Page 143 and 144: fixityspec :: Parser FixitySpec fix
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Write You a Haskell Stephen Diehl

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