Write You a Haskell Stephen Diehl

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, _flags :: Flags.Flags -- ^ Compiler flags , _venv :: CoreEval.ValEnv Core.Expr -- ^ Core interpreter environment , _denv :: DataEnv.DataEnv -- ^ Entity dictionary , _clenv :: ClassEnv.ClassHier -- ^ Typeclass hierarchy } deriving (Eq, Show) e compiler itself will have several entry points, expr for interactive evaluation that expects an expression object and joins it into accumulated interactive environment. And modl path that compile whole modules. roughout the next 10 chapters we will incrementally create a series of transformations with the following type signatures. parseP :: FilePath -> L.Text -> CompilerM Syn.Module dataP :: Syn.Module -> CompilerM Syn.Module groupP :: Syn.Module -> CompilerM Syn.Module renameP :: Syn.Module -> CompilerM Syn.Module desugarP :: Syn.Module -> CompilerM Syn.Module inferP :: Syn.Module -> CompilerM Core.Module evalP :: Core.Module -> CompilerM () e code path for modl is then simply the passes composed with the Kleisli composition operator to form the composite pipeline for compiling modules. (>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c And that’s basically the entire structure of the compiler. It’s just a pipeline of monadic actions for each pass rolled up inside of CompilerM. modl :: FilePath -> L.Text -> CompilerM () modl fname = parseP fname >=> dataP >=> groupP >=> renameP >=> desugarP >=> inferP >=> evalP Engineering Overview REPL It is extremely important to have an interactive shell to be able to interactively explore the compilation steps and intermediate forms for arbitrary expressions. GHCi does this very well, and nearly every intermediate form is inspectable. We will endeavor to recreate this experience with our toy language. 108
If the ProtoHaskell compiler is invoked either in GHCi or as standable executable, you will see a similar interactive shell. _ _ _ | ProtoHaskell Compiler 0.1.0 | | | | __ _ ___| | __ | Copyright (c) 2013-2015 Stephen Diehl | |_| |/ _‘ / __| |/ / | Released under the MIT License | _ | (_| \__ \ < | |_| |_|\__,_|___/_|\_\ | Type :help for help Compiling module: prelude.fun > id (1+2) 3 > :type (>>=) (>>=) :: Monad m => m a -> (a -> m b) -> m b > :set -ddump-rn > :load test.fun Command line conventions will follow the Haskell’s naming conventions. ere will be a strong emphasis on building debugging systems on top of our architecture so that when subtle bugs creep up you will have the tools to diagnose the internal state of the type system and detect flaws in the implementation. Command :browse :load :reload :edit :core :module :source :type :kind :set :unset :ekg :constraints :quit Action Browse the type signatures for a program Load a program from file Run the active file Edit the active file in system editor Show the core of an expression or program Show active modules imports Show the source code of an expression or program Show the type of an expression Show the kind of an expression Set a flag Unset a flag Start the EKG profiler as a background process Dump the typing constraints for an expression Exit interpreter e most notable difference is the very important :core command which will dump out the core representation of any expression given in the interactive shell. Also the :constraints which will interactively walk you through the type checker’s reasoning about it how derived the type it did for a given expression. ProtoHaskell> :type plus plus :: forall a. Num a => a -> a -> a 109
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 . . . . . . . . . . .
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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
Page 47 and 48:
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 and 108: • Higher order functions • Para
Page 109: • e PHOAS, the type-erased Core i
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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