Write You a Haskell Stephen Diehl

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let f x = x + 1 Let ”f” [] (Lam ”x” (Op Add [Var ”x”, Lit (LitInt 1)])) Inference will generate a system of constraints which are solved via a process known as unification to yield the type of the expression. Int -> Int -> Int ~ a -> b b ~ Int -> c f :: Int -> Int In some cases this type will be incorporated directly into the AST and the inference will transform the frontend language into an explicitly typed core language. Let ”f” [] (Lam ”x” (TArr TInt TInt) (App (App (Prim ”primAdd”) (Var ”x”)) (Lit (LitInt 1)))) Transformation e type core representation is often suitable for evaluation, but quite often different intermediate representations are more amenable to certain optimizations and make various semantic properties of the language explicit. ese kind of intermediate forms will often attach information about free variables, allocations, and usage information directly in the AST structure. e most important form we will use is called the Spineless Tagless G-Machine ( STG ), an abstract machine that makes many of the properties of lazy evaluation explicit directly in the AST. Code Generation From the core language we will either evaluate it on top of a high-level interpreter written in <strong>Haskell</strong> itself, or into another intermediate language like C or LLVM which can itself be compiled into native code. let f x = x + 1 Quite often this process will involve another intermediate representation which abstracts over the process of assigning and moving values between CPU registers and main memory. LLVM and GHC’s Cmm are two target languages serving this purpose. 12
f: mov res, arg add res, 1 ret define i32 @f(i32 %x) { entry: %add = add nsw i32 %x, 1 ret i32 %add } From here the target language can be compiled into the system’s assembly language. All code that is required for evaluation is linked into the resulting module. f: movl movl addl movl ret %edi, -4(%rsp) -4(%rsp), %edi $1, %edi %edi, %eax And ultimately this code will be assembled into platform specific instructions by the native code generator, encoded as a predefined sequence of CPU instructions defined by the processor specification. 0000000000000000 : 0: 89 7c 24 fc mov %edi,-0x4(%rsp) 4: 8b 7c 24 fc mov -0x4(%rsp),%edi 8: 81 c7 01 00 00 00 add $0x1,%edi e: 89 f8 mov %edi,%eax 10: c3 retq 13
Page 1 and 2: Write You a Haskell Building a mode
Page 3 and 4: Contents Introduction 6 Goals . . .
Page 5 and 6: Evaluation . . . . . . . . . . . .
Page 7 and 8: Syntax Errors . . . . . . . . . . .
Page 9 and 10: • containers • unordered-contai
Page 11 and 12: File ””, line 1, in TypeError:
Page 13: ] TokenSym ”x”, TokenAdd, Token
Page 17 and 18: Datatypes Constructors for datatype
Page 19 and 20: length :: [a] -> Int length [] = 0
Page 21 and 22: Higher-Kinded Types e “type of ty
Page 23 and 24: eturn a >>= f = f a Law 2 m >>= ret
Page 25 and 26: data PlatonicSolid = Tetrahedron |
Page 27 and 28: foo :: Stack () foo = Stack $ do pu
Page 29 and 30: , bar :: Int } deriving (Show) comp
Page 31 and 32: class IsString a where fromString :
Page 33 and 34: Parsing Parser Combinators For pars
Page 35 and 36: instance Monad Parser where return
Page 37 and 38: natural :: Parser Integer natural =
Page 39 and 40: print $ eval $ run a Now we can try
Page 41 and 42: module Syntax where data Expr = Tr
Page 43 and 44: cannot proceed because the reductio
Page 45 and 46: later into native CPU instructions
Page 47 and 48: λx.e ere are several syntactical c
Page 49 and 50: type Name = String data Expr = Var
Page 51 and 52: Eta-expansion (λx.ex)e ′ β →
Page 53 and 54: Y = SSK(S(K(SS(S(SSK))))K) In a unt
Page 55 and 56: parensIf :: Bool -> Doc -> Doc pare
Page 57 and 58: In this notation, the expression ab
Page 59 and 60: In all the languages which we will
Page 61 and 62: eval1 expr = case expr of Succ t ->
Page 63 and 64: TNat -> return TNat _ -> throwError
Page 65 and 66:
• T-Var Variables are simply pull
Page 67 and 68:
t1 throwError $ Mismatch t2 a ty -
Page 69 and 70:
Full Source • Typed Arithmetic
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1. Evaluate f to λy.e 2. Evaluate
Page 73 and 74:
e 1 → e ′ 1 e 1 e 2 → e ′ 1
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case we will use a GADT to embed a
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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
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As before let rec expressions will
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Γ, x : τ = (Γ\x) ∪ {x : τ} Op
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where s’ = foldr Map.delete s as
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s2 Type -> Infer Subst bind a t |
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infer :: TypeEnv -> Expr -> Infer (
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App e1 e2 -> do tv
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-- | Unify two types uni :: Type ->
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unifies t (TVar v) = v ‘bind‘ t
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Interpreter Our evaluator will oper
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Our language can be compiled into a
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exec True contents -- :type command
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let rec fib n = if (n == 0) then 0
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• Higher order functions • Para
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• e PHOAS, the type-erased Core i
Page 111 and 112:
If the ProtoHaskell compiler is inv
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infixl 6 + infixl 7 * f = 1 + 2 * 3
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-- Desugared f x = case x of Just _
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data Kind = KStar | KArr Kind Kind
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TypeError) -- | Inference state dat
Page 121 and 122:
e expression or Expr type is the co
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data qname [var] where [tydecl] dat
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Typeclass Declarations Typeclass de
Page 127 and 128:
Syntax Name Kind Description (,) Pa
Page 129 and 130:
So for instance if we have three AS
Page 131 and 132:
-- **Begin Haskell Syntax** { {-# O
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tokens :- -- Whitespace insensitive
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Expr : let VAR ’=’ Expr in Expr
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data Type = TVar Loc TVar | TCon Lo
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-- Start of layout ( Column: 0 ) fi
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Extensible Operators Haskell famous
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fixityspec :: Parser FixitySpec fix
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Write You a Haskell Stephen Diehl

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