Write You a Haskell Stephen Diehl

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Write You a Haskell by Stephen Diehl Copyright © 2013-2015. www.stephendiehl.com is written work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. You may reproduce and edit this work with attribution for all non-commercial purposes. e included source is released under the terms of the MIT License. Git commit: 23a5afe76a51032ecfd08ac8c69932364520906c
Contents Introduction 6 Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Concepts 7 Functional Languages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Static Typing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Functional Compilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Parsing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Desugaring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Type Inference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Transformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Code Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Haskell Basics 14 Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Datatypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Pattern matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Recursion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Laziness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Higher-Kinded Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Typeclasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Monads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Applicatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Monoids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Deriving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 IO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Monad Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 1
Page 1: Write You a Haskell Building a mode
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 and 14: ] TokenSym ”x”, TokenAdd, Token
Page 15 and 16: f: mov res, arg add res, 1 ret defi
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
Page 71 and 72:
1. Evaluate f to λy.e 2. Evaluate
Page 73 and 74:
e 1 → e ′ 1 e 1 e 2 → e ′ 1
Page 75 and 76:
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 ->
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unifies t (TVar v) = v ‘bind‘ t
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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
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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
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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
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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