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Refactor and add tutorial to README.md
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Benno Fünfstück
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101
README.md
101
README.md
@ -1,6 +1,105 @@
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haskell-generate
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====================
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================
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[](http://travis-ci.org/bennofs/haskell-generate)
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## Introduction
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If you want to generate haskell source code, you could build up haskell-src-exts AST and then pretty print it. But that's easy to screw up, because haskell-src-exts doesn't include tag it's AST with a type. This library aims to fill the gap, adding type information to haskell-src-exts expressions and also managing imports for you.
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## Getting started
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First, you need to import this library:
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```haskell
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import Language.Haskell.Generate
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```
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This module reexports `Language.Haskell.Exts.Syntax`, because haskell-generate builds on top of that.
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There are two main types in haskell-generate. The first is the monad `Generate` and the type alias `ExpG`. The `Generate` monad is used to track required imports. It also allows to generate unique names. `ExpG t` is just an action in the `Generate` monad that returns an expression of type `t`.
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How do you build expressions? There is a number of predefined expressions for the functions in the
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Prelude. This allows you to just use these and combine them to new expressions. For example, let's define a expression that reads a file called "names":
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```haskell
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readNamesFile' :: ExpG (IO String)
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readNamesFile' = readFile' <>$ expr "names"
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```
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Here we use `(<>$)` to apply the `readFile'` expression to the string `names`. `readFile'` is one of the expressions already provided by haskell-generate. All expressions that are provided by haskell-generate end with an apostrophe. You can find more of them in the module `Language.Haskell.Generate.PreludeDef`. The `expr` function is used to lift the string `names` into an expression of type `ExpG String`.
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Now that we have an expression, we need to bind it to a name in a module. For this job, we use another monad, the `ModuleM` monad. It allows you to bind expressions to names and then generate
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a module with those names.
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Here's how we generate our module:
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```haskell
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myModule :: ModuleG
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myModule = do
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d <- addDecl (Ident "main") $ applyE2 bind' readNamesFile' putStrLn'
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return $ Just [exportFun d]
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```
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`ModuleG` is again a type synonym for an action in the `ModuleM` monad. It must either return Nothing (which omits the export list) or an export list. In this case, we export the "main" function, which we previously defined using `addDecl`.
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The only thing left to do is to generate the actual source code for the module, for which we
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use the `generateModule` function, which takes the module name as an argument:
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```haskell
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main :: IO ()
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main = putStrLn $ generateModule myModule "Main"
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```
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If you run the program, you'll get the following output:
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```haskell
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module Main (main) where
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import qualified GHC.Base
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import qualified System.IO
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main
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= (GHC.Base.>>=) (System.IO.readFile ['n', 'a', 'm', 'e', 's'])
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System.IO.putStrLn
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```
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If you run this code, you'll get the contents of the "names" file. The code is a bit ugly and uses
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qualified imports to avoid name clashes, but it works.
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## Importing functions
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Until now, we've only used the predefined expressions from `Language.Haskell.Generate.PreludeDef`, but often you'll want to use definitions from other modules that you might want to use.
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You can do that using the `useValue` from haskell-generate. Let's look at the type of `useValue`:
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```haskell
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useValue :: String -> Name -> ExpG t
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```
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`useValue` takes a module name in which the function is defined and the name of the function. It returns an expression of any type you which. This function is unsafe, because it cannot check that the returned type is actually the type of the function. That's why you usually given `useValue` an explicit type signature.
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For example, suppose we want to use the function `permutations` from Data.List. We write the following definition for it:
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```haskell
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permutations' :: ExpG ([a] -> [[a]]) -- Here we given an explicit type for permutations'. This is not checked, so make sure it's actually right!
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permutations' = useValue "Data.List" (Ident "permutations") -- "permutations" is an identifier, not a symbol, so we use the "Ident" constructor.
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```
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## Using TH to automagically import functions
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If the function you want to import is already available at compile time, you can use the template haskell code from `Language.Haskell.Generate.TH` to generate the expression definitions. This is the approach we use for the Prelude, as an example.
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Using the example from the previous section, we could also import the `permutations` function like this:
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```haskell
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-- at the top of the file:
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{-# LANGUAGE TemplateHaskell #-} -- Enable template haskell
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import Data.List (permutations) -- The function needs to be available at compile time
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declareFunction 'permutations -- This generates the same code as above, but is more type-safe because you don't have to specify the type yourself.
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```
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## Contributing
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If you have an idea, a question or a bug report, open an issue on github. You can also find me on freenode in the #haskell channel, my nick is bennofs.
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@ -37,7 +37,8 @@ library
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, template-haskell
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exposed-modules:
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Language.Haskell.Generate
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Language.Haskell.Generate.Base
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Language.Haskell.Generate.Monad
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Language.Haskell.Generate.Expression
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Language.Haskell.Generate.TH
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Language.Haskell.Generate.PreludeDef
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@ -2,5 +2,6 @@ module Language.Haskell.Generate
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( module X
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) where
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import Language.Haskell.Generate.Base as X
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import Language.Haskell.Exts.Syntax as X
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import Language.Haskell.Generate.Monad as X
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import Language.Haskell.Generate.PreludeDef as X
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12
src/Language/Haskell/Generate/Expression.hs
Normal file
12
src/Language/Haskell/Generate/Expression.hs
Normal file
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module Language.Haskell.Generate.Expression
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( Expression(..)
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, app
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) where
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import Language.Haskell.Exts.Syntax
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newtype Expression t = Expression { runExpression :: Exp }
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app :: Expression (a -> b) -> Expression a -> Expression b
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app (Expression a) (Expression b) = Expression $ App a b
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@ -3,9 +3,10 @@
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{-# LANGUAGE ScopedTypeVariables #-}
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{-# LANGUAGE UndecidableInstances #-}
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{-# LANGUAGE FlexibleInstances #-}
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module Language.Haskell.Generate.Base
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( ExpM(..), ExpG, ExpType
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, runExpM, newName
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module Language.Haskell.Generate.Monad
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( Generate(..), ExpG
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, runGenerate, newName
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, returnE
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, useValue, useCon, useVar
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, caseE
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, applyE, applyE2, applyE3, applyE4, applyE5, applyE6
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@ -19,6 +20,7 @@ module Language.Haskell.Generate.Base
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, addDecl
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, runModuleM
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, generateModule
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, generateExp
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)
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where
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@ -31,32 +33,30 @@ import qualified Data.Set as S
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import Language.Haskell.Exts.Pretty
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import Language.Haskell.Exts.SrcLoc
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import Language.Haskell.Exts.Syntax
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import Language.Haskell.Generate.Expression
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--------------------------------------------------------------------------------
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-- Generate expressions
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-- | A ExpM is a monad used to track the imports that are needed for a given expression. Usually, you don't have to use
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-- this type directly, but use combinators to combine several ExpM into bigger expressions. The t type parameter tracks
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-- the type of the expression, so you don't accidently build expression that don't type check.
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newtype ExpM t a = ExpM { unExpM :: StateT Integer (Writer (S.Set ModuleName)) a } deriving (Functor, Applicative, Monad)
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newtype Generate a = Generate { unGenerate :: StateT Integer (Writer (S.Set ModuleName)) a } deriving (Functor, Applicative, Monad)
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-- | The ExpG type is a ExpM computation that returns an expression. Usually, this is the end result of a function generating
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-- a haskell expression
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type ExpG t = ExpM t Exp
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runGenerate :: Generate a -> (a, S.Set ModuleName)
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runGenerate (Generate a) = runWriter $ evalStateT a 0
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-- | Evaluate a ExpM action, returning the needed modules and the value.
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runExpM :: ExpM t a -> (a, S.Set ModuleName)
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runExpM (ExpM expt) = runWriter $ evalStateT expt 0
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type ExpG t = Generate (Expression t)
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unsafeCoerceE :: ExpM t a -> ExpM t' a
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unsafeCoerceE (ExpM x) = ExpM x
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returnE :: Exp -> ExpG t
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returnE = return . Expression
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generateExp :: ExpG t -> String
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generateExp = prettyPrint . runExpression . fst . runGenerate
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-- | Generate a case expression.
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caseE :: ExpG x -> [(Pat, ExpG t)] -> ExpG t
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caseE v alt = do
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v' <- unsafeCoerceE v
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alt' <- mapM (\(p,a) -> fmap (\a' -> Alt noLoc p (UnGuardedAlt a') (BDecls [])) a) alt
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return $ Case v' alt'
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v' <- v
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alt' <- mapM (\(p,a) -> fmap (\a' -> Alt noLoc p (UnGuardedAlt $ runExpression a') (BDecls [])) a) alt
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return $ Expression $ Case (runExpression v') alt'
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-- | Import a function from a module. This function is polymorphic in the type of the resulting expression,
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-- you should probably only use this function to define type-restricted specializations.
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@ -67,31 +67,27 @@ caseE v alt = do
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-- > addInt = useValue "Prelude" $ Symbol "+"
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--
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useValue :: String -> Name -> ExpG a
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useValue md name = ExpM $ do
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useValue md name = Generate $ do
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lift $ tell $ S.singleton $ ModuleName md
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return $ Var $ Qual (ModuleName md) name
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return $ Expression $ Var $ Qual (ModuleName md) name
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-- | Import a value constructor from a module. Returns the qualified name of the constructor.
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useCon :: String -> Name -> ExpM t QName
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useCon md name = ExpM $ do
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useCon :: String -> Name -> Generate QName
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useCon md name = Generate $ do
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lift $ tell $ S.singleton $ ModuleName md
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return $ Qual (ModuleName md) name
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-- | Use the value of a variable with the given name.
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useVar :: Name -> ExpG t
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useVar name = return $ Var $ UnQual name
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useVar name = return $ Expression $ Var $ UnQual name
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-- | Generate a new unique variable name with the given prefix. Note that this new variable name
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-- is only unique relative to other variable names generated by this function.
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newName :: String -> ExpM t Name
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newName pref = ExpM $ do
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newName :: String -> Generate Name
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newName pref = Generate $ do
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i <- get <* modify succ
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return $ Ident $ pref ++ show i
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-- | This type family can be used to get the type associated with some expression.
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type family ExpType a :: *
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type instance ExpType (ExpM t a) = t
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-- | Generate a expression from a haskell value.
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class GenExp t where
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type GenExpType t :: *
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@ -103,36 +99,43 @@ instance GenExp (ExpG a) where
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type GenExpType (ExpG a) = a
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expr = id
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instance GenExp (Expression t) where
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type GenExpType (Expression t) = t
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expr = return
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instance GenExp Char where
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type GenExpType Char = Char
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expr = return . Lit . Char
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expr = return . Expression . Lit . Char
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instance GenExp Integer where
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type GenExpType Integer = Integer
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expr = return . Lit . Int
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expr = return . Expression . Lit . Int
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instance GenExp Rational where
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type GenExpType Rational = Rational
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expr = return . Lit . Frac
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expr = return . Expression . Lit . Frac
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instance GenExp a => GenExp [a] where
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type GenExpType [a] = [GenExpType a]
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expr = ExpM . fmap List . mapM (unExpM . expr)
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expr = Generate . fmap (Expression . List . map runExpression) . mapM (unGenerate . expr)
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instance GenExp x => GenExp (ExpG a -> x) where
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type GenExpType (ExpG a -> x) = a -> GenExpType x
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expr f = do
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pvarName <- newName "pvar_"
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body <- unsafeCoerceE $ expr $ f $ return $ Var $ UnQual pvarName
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return $ Lambda noLoc [PVar pvarName] body
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body <- expr $ f $ return $ Expression $ Var $ UnQual pvarName
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return $ Expression $ Lambda noLoc [PVar pvarName] $ runExpression body
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--------------------------------------------------------------------------------
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-- Apply functions
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-- | Apply a function in a haskell expression to a value.
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applyE :: ExpG (a -> b) -> ExpG a -> ExpG b
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applyE a b = unsafeCoerceE $ liftM (foldl1 App) $ sequence [ce a,ce b]
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where ce = unsafeCoerceE
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applyE a b = wrap $ liftM (foldl1 App) $ sequence [unwrap a, unwrap b]
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where wrap = fmap Expression
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unwrap = fmap runExpression
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-- | Operator for 'applyE'.
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(<>$) :: ExpG (a -> b) -> ExpG a -> ExpG b
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@ -142,28 +145,33 @@ infixl 1 <>$
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-- | ApplyE for 2 arguments
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applyE2 :: ExpG (a -> b -> c) -> ExpG a -> ExpG b -> ExpG c
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applyE2 a b c = unsafeCoerceE $ liftM (foldl1 App) $ sequence [ce a,ce b,ce c]
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where ce = unsafeCoerceE
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applyE2 a b c = wrap $ liftM (foldl1 App) $ sequence [unwrap a,unwrap b,unwrap c]
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where wrap = fmap Expression
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unwrap = fmap runExpression
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-- | Apply a function to 3 arguments
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applyE3 :: ExpG (a -> b -> c -> d) -> ExpG a -> ExpG b -> ExpG c -> ExpG d
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applyE3 a b c d = unsafeCoerceE $ liftM (foldl1 App) $ sequence [ce a,ce b,ce c,ce d]
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where ce = unsafeCoerceE
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applyE3 a b c d = wrap $ liftM (foldl1 App) $ sequence [unwrap a,unwrap b,unwrap c,unwrap d]
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where wrap = fmap Expression
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unwrap = fmap runExpression
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-- | Apply a function to 4 arguments
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applyE4 :: ExpG (a -> b -> c -> d -> e) -> ExpG a -> ExpG b -> ExpG c -> ExpG d -> ExpG e
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applyE4 a b c d e = unsafeCoerceE $ liftM (foldl1 App) $ sequence [ce a,ce b,ce c,ce d,ce e]
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where ce = unsafeCoerceE
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applyE4 a b c d e = wrap $ liftM (foldl1 App) $ sequence [unwrap a,unwrap b,unwrap c,unwrap d,unwrap e]
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where wrap = fmap Expression
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unwrap = fmap runExpression
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-- | Apply a function to 5 arguments
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applyE5 :: ExpG (a -> b -> c -> d -> e -> f) -> ExpG a -> ExpG b -> ExpG c -> ExpG d -> ExpG e -> ExpG f
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applyE5 a b c d e f = unsafeCoerceE $ liftM (foldl1 App) $ sequence [ce a,ce b,ce c,ce d,ce e,ce f]
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where ce = unsafeCoerceE
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applyE5 a b c d e f = wrap $ liftM (foldl1 App) $ sequence [unwrap a,unwrap b,unwrap c,unwrap d,unwrap e,unwrap f]
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where wrap = fmap Expression
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unwrap = fmap runExpression
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-- | Apply a function to 6 arguments
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applyE6 :: ExpG (a -> b -> c -> d -> e -> f -> g) -> ExpG a -> ExpG b -> ExpG c -> ExpG d -> ExpG e -> ExpG f -> ExpG g
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applyE6 a b c d e f g = unsafeCoerceE $ liftM (foldl1 App) $ sequence [ce a,ce b,ce c,ce d,ce e,ce f,ce g]
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where ce = unsafeCoerceE
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applyE6 a b c d e f g = wrap $ liftM (foldl1 App) $ sequence [unwrap a,unwrap b,unwrap c,unwrap d,unwrap e,unwrap f,unwrap g]
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where wrap = fmap Expression
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unwrap = fmap runExpression
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--------------------------------------------------------------------------------
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-- Generate modules
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@ -180,7 +188,7 @@ data FunRef t = FunRef Name
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instance GenExp (FunRef t) where
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type GenExpType (FunRef t) = t
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expr (FunRef n) = return $ Var $ UnQual n
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expr (FunRef n) = return $ Expression $ Var $ UnQual n
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-- | Generate a ExportSpec for a given function item.
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exportFun :: FunRef t -> ExportSpec
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@ -189,8 +197,8 @@ exportFun (FunRef name) = EVar (UnQual name)
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-- | Add a declaration to the module. Return a reference to it that can be used to either apply the function to some values or export it.
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addDecl :: Name -> ExpG t -> ModuleM (FunRef t)
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addDecl name e = ModuleM $ do
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let (body, mods) = runExpM e
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tell (mods, [FunBind [Match noLoc name [] Nothing (UnGuardedRhs body) $ BDecls []]])
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let (body, mods) = runGenerate e
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tell (mods, [FunBind [Match noLoc name [] Nothing (UnGuardedRhs $ runExpression body) $ BDecls []]])
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return $ FunRef name
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-- | Extract the Module from a module generator.
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@ -6,7 +6,7 @@
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module Language.Haskell.Generate.PreludeDef where
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import Language.Haskell.Exts.Syntax
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import Language.Haskell.Generate.Base
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import Language.Haskell.Generate.Monad
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import Language.Haskell.Generate.TH
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--------------------------------------------------------------------------------
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@ -66,22 +66,22 @@ fmap concat $ mapM declareNamedSymbol
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(<>.) a b = dot' <>$ a <>$ b
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tuple0 :: ExpG ()
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tuple0 = return $ Var $ Special UnitCon
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tuple0 = returnE $ Var $ Special UnitCon
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tuple2 :: ExpG (a -> b -> (a,b))
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tuple2 = return $ Var $ Special $ TupleCon Boxed 2
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tuple2 = returnE $ Var $ Special $ TupleCon Boxed 2
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tuple3 :: ExpG (a -> b -> c -> (a,b,c))
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tuple3 = return $ Var $ Special $ TupleCon Boxed 3
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tuple3 = returnE $ Var $ Special $ TupleCon Boxed 3
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tuple4 :: ExpG (a -> b -> c -> d -> (a,b,c,d))
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tuple4 = return $ Var $ Special $ TupleCon Boxed 4
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tuple4 = returnE $ Var $ Special $ TupleCon Boxed 4
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tuple5 :: ExpG (a -> b -> c -> d -> (a,b,c,d,e))
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tuple5 = return $ Var $ Special $ TupleCon Boxed 5
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tuple5 = returnE $ Var $ Special $ TupleCon Boxed 5
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cons :: ExpG (a -> [a] -> [a])
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cons = return $ Var $ Special Cons
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cons = returnE $ Var $ Special Cons
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instance Num t => Num (ExpG t) where
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a + b = add' <>$ a <>$ b
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@ -89,6 +89,6 @@ instance Num t => Num (ExpG t) where
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a * b = mult' <>$ a <>$ b
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negate a = negate' <>$ a
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abs a = abs' <>$ a
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fromInteger a = return $ Lit $ Int a
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fromInteger a = returnE $ Lit $ Int a
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signum a = signum' <>$ a
|
||||
|
||||
|
||||
@ -10,7 +10,7 @@ module Language.Haskell.Generate.TH
|
||||
|
||||
import Data.Char
|
||||
import Language.Haskell.Exts.Syntax hiding (Name)
|
||||
import Language.Haskell.Generate.Base hiding (Name)
|
||||
import Language.Haskell.Generate.Monad hiding (Name)
|
||||
import Language.Haskell.TH
|
||||
import Language.Haskell.TH.Syntax
|
||||
|
||||
@ -36,9 +36,13 @@ declareNamedThing (thing, name, thingClass) = do
|
||||
[| useValue $(lift md) $ $(conE thingClass) $(lift $ nameBase thing) |]
|
||||
]
|
||||
|
||||
where overQuantifiedType f (ForallT bnds ctx t) = ForallT bnds ctx $ overQuantifiedType f t
|
||||
where overQuantifiedType f (ForallT bnds ctx t) = ForallT (map removeKind bnds) ctx $ overQuantifiedType f t
|
||||
overQuantifiedType f x = f x
|
||||
|
||||
removeKind :: TyVarBndr -> TyVarBndr
|
||||
removeKind (KindedTV n _) = PlainTV n
|
||||
removeKind x = x
|
||||
|
||||
-- | Declare a symbol, using the given name for the definition.
|
||||
declareNamedSymbol :: (Name, String) -> DecsQ
|
||||
declareNamedSymbol (func, name) = declareNamedThing (func, name, 'Symbol)
|
||||
|
||||
Loading…
Reference in New Issue
Block a user