Write You a Haskell Stephen Diehl

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• Any GHC-specific language extensions. • Newtypes • Module namespaces • Operator parameters • Defaulting rules • Exceptions • Parallelism • Software Transactional Memory • Foreign Function Interface Now if one feels so inclined one could of course implement these features on top our final language, but they are left as an exercise to the reader! is of course begs the question of whether or not our language is “a Haskell”. In the strictest sense, it will not be since it doesn’t fully conform to either the Haskell 98 or Haskell 2010 language specifications. However in terms of the colloquial usage of the term Haskell, there does seem to be some growing feeling that the “Haskell language family” does exist as a definable subset of the functional programming design space, although many people disagree what its defining features are. In this sense we will most certainly be writing a language in the Haskell family. Intermediate Forms e passes between each of the phases make up the main compilation pipeline . For ProtoHaskell our pipeline consists of the transitions between four intermediate forms of the program. • e Source, the textual representation of the program from a file or user input. is is stored in a Text type. • e Frontend source, the untyped AST generated from the parser. • e Core, the explicitly typed, desugared form of the program generated after type inference. 106
• e PHOAS, the type-erased Core is transformed into Haskell expressions by mapping lambda expressions in our language directly into Haskell lambda expressions and then evaluated using the Haskell runtime. Pass Rep Haskell Type Parsing Source Text.Text Desugaring Frontend Frontend.Expr Typechecking Core Core.Expr Evaluation PHOAS CoreEval.ExprP For our later Fun language our pipeline builds on top of the ProtoHaskell but instead of going to an interpreter it will be compiled into native code through the native code generator (on top of LLVM) and compiled into a binary executable or evaluated by a just-in-time (JIT) compiler. Pass Rep Haskell Type Parsing Source Text.Text Desugaring Frontend Frontend.Expr Typechecking Core Core.Expr Transformation STG STG.Expr Transformation Imp Imp.Expr Code Generation LLVM LLVM.General.Module CompilerM e main driver of the compiler will be a ExceptT + State + IO transformer stack . All other passes and transformations in the compiler will hang off of this monad, which encapsulates the main compilation pipeline. type CompilerMonad = ExceptT Msg (StateT CompilerState IO) data CompilerState = CompilerState { _fname :: Maybe FilePath -- ^ File path , _imports :: [FilePath] -- ^ Loaded modules , _src :: Maybe L.Text -- ^ File source , _ast :: Maybe Syn.Module -- ^ Frontend AST , _tenv :: Env.Env -- ^ Typing environment , _kenv :: Map.Map Name Kind -- ^ Kind environment , _cenv :: ClassEnv.ClassEnv -- ^ Typeclass environment , _cast :: Maybe Core.Module -- ^ Core AST 107
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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
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 ->
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: • Higher order functions • Para
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 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
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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