/
Eval.hs
440 lines (388 loc) · 16.1 KB
/
Eval.hs
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{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE ApplicativeDo #-}
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE MultiWayIf #-}
{-# LANGUAGE PartialTypeSignatures #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TupleSections #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}
{-# OPTIONS_GHC -fno-warn-name-shadowing #-}
module Nix.Eval where
import Control.Arrow (first)
import Control.Monad
import Control.Monad.Fix
import Control.Monad.State
import Data.Align.Key
import Data.Fix
import Data.Functor.Compose
import Data.HashMap.Lazy (HashMap)
import qualified Data.HashMap.Lazy as M
import Data.List (intercalate, partition, foldl')
import Data.List.NonEmpty (NonEmpty(..))
import qualified Data.List.NonEmpty as NE
import Data.Maybe (fromMaybe, catMaybes)
import Data.Text (Text)
import qualified Data.Text as Text
import Data.These
import Data.Traversable (for)
import Data.Void
import Nix.Atoms
import Nix.Convert
import Nix.Expr
import Nix.Pretty
import Nix.Scope
import Nix.Stack
import Nix.StringOperations (runAntiquoted)
import Nix.Thunk
import Nix.Utils
-- import System.IO.Unsafe -- move this into a tracing module
class (Show v, Monad m) => MonadEval v m | v -> m where
freeVariable :: Text -> m v
evalCurPos :: m v
evalConstant :: NAtom -> m v
evalString :: Text -> DList Text -> m v
evalLiteralPath :: FilePath -> m v
evalEnvPath :: FilePath -> m v
evalUnary :: NUnaryOp -> v -> m v
evalBinary :: NBinaryOp -> v -> m v -> m v
-- ^ The second argument is an action because operators such as boolean &&
-- and || may not evaluate the second argument.
evalWith :: m v -> m v -> m v
evalIf :: v -> m v -> m v -> m v
evalAssert :: v -> m v -> m v
evalApp :: v -> m v -> m v
evalAbs :: Params Void -> (m v -> m v) -> m v
evalError :: String -> m a
type MonadNixEval e v t m =
(MonadEval v m, Scoped e t m, MonadThunk v t m, MonadFix m,
Framed e m, MonadFile m, MonadVar m,
ToValue Bool m v, ToValue [t] m v,
FromValue (Text, DList Text) m v,
ToValue (AttrSet t) m v, FromValue (AttrSet t) m v,
ToValue (AttrSet t, AttrSet SourcePos) m v,
FromValue (AttrSet t, AttrSet SourcePos) m v)
wrapExpr :: NExprF (m v) -> NExpr
wrapExpr x = Fix (Fix (NSym "<?>") <$ x)
exprFContext :: (Framed e m) => NExprF (m v) -> m r -> m r
exprFContext e = withStringContext $
"While forcing thunk for: " ++ show (prettyNix (wrapExpr e)) ++ "\n"
-- | Evaluate an nix expression, with a given NThunkSet as environment
evalExpr :: MonadNixEval e v t m => NExpr -> m v
evalExpr = cata eval
eval :: forall e v t m. MonadNixEval e v t m => NExprF (m v) -> m v
eval (NSym "__curPos") = evalCurPos
eval (NSym var) = lookupVar var >>= \case
Nothing -> freeVariable var
Just v -> force v pure
eval (NConstant x) = evalConstant x
eval (NStr str) = uncurry evalString =<< assembleString str
eval (NLiteralPath p) = evalLiteralPath p
eval (NEnvPath p) = evalEnvPath p
eval (NUnary op arg) = evalUnary op =<< arg
eval (NBinary NApp fun arg) = do
traceM "NApp"
scope <- currentScopes @_ @t
evalApp ?? withScopes scope arg =<< fun
eval (NBinary op larg rarg) = larg >>= \lval -> evalBinary op lval rarg
eval (NSelect aset attr alt) = do
traceM "NSelect"
mres <- evalSelect aset attr
traceM "NSelect..2"
case mres of
Right v -> pure v
Left (s, ks) -> fromMaybe err alt
where
err = evalError @v $ "Could not look up attribute "
++ intercalate "." (map Text.unpack (NE.toList ks))
++ " in " ++ show @v s
eval (NHasAttr aset attr) = do
traceM "NHasAttr"
toValue . either (const False) (const True) =<< evalSelect aset attr
eval e@(NList l) = do
traceM "NList"
scope <- currentScopes
toValue =<< for l (thunk . exprFContext e . withScopes @t scope)
eval e@(NSet binds) = do
traceM "NSet..1"
(s, p) <- evalBinds e True False binds
traceM $ "NSet..2: s = " ++ show (void s)
traceM $ "NSet..2: p = " ++ show (void p)
toValue (s, p)
eval e@(NRecSet binds) = do
traceM "NRecSet..1"
(s, p) <- evalBinds e True True (desugarBinds (eval . NRecSet) binds)
traceM $ "NRecSet..2: s = " ++ show (void s)
traceM $ "NRecSet..2: p = " ++ show (void p)
toValue (s, p)
eval e@(NLet binds body) = do
traceM "Let..1"
(s, _) <- evalBinds e True True (NE.toList binds)
traceM $ "Let..2: s = " ++ show (void s)
pushScope s body
eval (NIf cond t f) = cond >>= \v -> evalIf v t f
eval (NWith scope body) = evalWith scope body
eval (NAssert cond body) = cond >>= \v -> evalAssert v body
eval e@(NAbs params body) = do
-- It is the environment at the definition site, not the call site, that
-- needs to be used when evaluating the body and default arguments, hence
-- we defer here so the present scope is restored when the parameters and
-- body are forced during application.
traceM "NAbs"
scope <- currentScopes @_ @t
evalAbs (clearDefaults params) $ \arg ->
-- jww (2018-04-17): We need to use the bound library here, so that
-- the body is only evaluated once.
withScopes @t scope $ do
args <- buildArgument e params arg
pushScope args body
where
clearDefaults :: Params r -> Params Void
clearDefaults (Param name) = Param name
clearDefaults (ParamSet xs b mv) = ParamSet (map (Nothing <$) xs) b mv
-- | If you know that the 'scope' action will result in an 'AttrSet t', then
-- this implementation may be used as an implementation for 'evalWith'.
evalWithAttrSet :: forall e v t m. MonadNixEval e v t m => m v -> m v -> m v
evalWithAttrSet scope body = do
-- The scope is deliberately wrapped in a thunk here, since it is
-- evaluated each time a name is looked up within the weak scope, and
-- we want to be sure the action it evaluates is to force a thunk, so
-- its value is only computed once.
traceM "Evaluating with scope"
cur <- currentScopes @_ @t
s <- thunk $ exprFContext (NWith scope body)
$ withScopes cur scope
pushWeakScope ?? body $ force s $ fromValue @(AttrSet t)
attrSetAlter :: forall e v t m. MonadNixEval e v t m
=> [Text]
-> AttrSet (m v)
-> m v
-> m (AttrSet (m v))
attrSetAlter [] _ _ = evalError @v "invalid selector with no components"
attrSetAlter (p:ps) m val = case M.lookup p m of
Nothing
| null ps -> go
| otherwise -> recurse M.empty
Just x
| null ps -> go
| otherwise ->
x >>= fromValue >>= \s -> recurse (force ?? pure <$> s)
where
go = return $ M.insert p val m
-- jww (2018-04-13): Need to record positions for attr paths as well
recurse s = attrSetAlter ps s val <&> \m' ->
M.insert p (toValue =<< fmap (value @_ @_ @m) <$> sequence m') m
desugarBinds :: forall r. ([Binding r] -> r) -> [Binding r] -> [Binding r]
desugarBinds embed binds = evalState (mapM (go <=< collect) binds) M.empty
where
collect :: Binding r
-> State (HashMap VarName (Maybe SourcePos, [Binding r]))
(Either VarName (Binding r))
collect (NamedVar (StaticKey x p:|y:ys) val) = do
m <- get
let v = case M.lookup x m of
Nothing -> (p, [NamedVar (y:|ys) val])
Just (p, v) -> (p, NamedVar (y:|ys) val : v)
put $ M.insert x v m
pure $ Left x
collect x = pure $ Right x
go :: Either VarName (Binding r)
-> State (HashMap VarName (Maybe SourcePos, [Binding r]))
(Binding r)
go (Right x) = pure x
go (Left x) = do
Just (p, v) <- gets $ M.lookup x
pure $ NamedVar (StaticKey x p :| []) (embed v)
evalBinds :: forall e v t m. MonadNixEval e v t m
=> NExprF (m v)
-> Bool
-> Bool
-> [Binding (m v)]
-> m (AttrSet t, AttrSet SourcePos)
evalBinds e allowDynamic recursive binds = do
scope <- currentScopes @_ @t
buildResult scope . concat =<< mapM (go scope) (moveOverridesLast binds)
where
moveOverridesLast = (\(x, y) -> y ++ x) .
partition (\case NamedVar (StaticKey "__overrides" _ :| []) _ -> True
_ -> False)
go :: Scopes m t -> Binding (m v) -> m [([Text], Maybe SourcePos, m v)]
go _ (NamedVar (StaticKey "__overrides" _ :| []) finalValue) =
finalValue >>= fromValue >>= \(o', p') ->
return $ map (\(k, v) -> ([k], M.lookup k p', force v pure))
(M.toList o')
go _ (NamedVar pathExpr finalValue) = do
let go :: NAttrPath (m v) -> m ([Text], Maybe SourcePos, m v)
go = \case
h :| t -> evalSetterKeyName allowDynamic h >>= \case
(Nothing, _) ->
pure ([], Nothing,
toValue (mempty :: AttrSet t))
(Just k, pos) -> case t of
[] -> pure ([k], pos, finalValue)
x:xs -> do
(restOfPath, _, v) <- go (x:|xs)
pure (k : restOfPath, pos, v)
go pathExpr <&> \case
-- When there are no path segments, e.g. `${null} = 5;`, we don't
-- bind anything
([], _, _) -> []
result -> [result]
go scope (Inherit ms names) = fmap catMaybes $ forM names $ \name ->
evalSetterKeyName allowDynamic name >>= \case
(Nothing, _) -> return Nothing
(Just key, pos) -> return $ Just ([key], pos, do
mv <- case ms of
Nothing -> withScopes scope $ lookupVar key
Just s -> s >>= fromValue @(AttrSet t) >>= \s ->
clearScopes @t $ pushScope s $ lookupVar key
case mv of
Nothing -> evalError @v $ "Inheriting unknown attribute: "
++ show (void name)
Just v -> force v pure)
buildResult :: Scopes m t
-> [([Text], Maybe SourcePos, m v)]
-> m (AttrSet t, AttrSet SourcePos)
buildResult scope bindings = do
s <- foldM insert M.empty bindings
res <- if recursive
then loebM (encapsulate <$> s)
else traverse (thunk . exprFContext e . withScopes scope) s
return (res, foldl' go M.empty bindings)
where
-- jww (2018-04-13): Need to record positions for attr paths as well
go m ([k], Just pos, _) = M.insert k pos m
go m _ = m
encapsulate f attrs =
thunk . exprFContext e
. withScopes scope
. pushScope attrs $ f
insert m (path, _, value) = attrSetAlter path m value
evalSelect :: forall e v t m. MonadNixEval e v t m
=> m v
-> NAttrPath (m v)
-> m (Either (v, NonEmpty Text) v)
evalSelect aset attr = do
traceM "evalSelect"
s <- aset
traceM "evalSelect..2"
path <- evalSelector True attr
traceM $ "evalSelect..3: " ++ show path
res <- extract s path
traceM "evalSelect..4"
return res
where
extract x path@(k:|ks) = fromValueMay x >>= \case
Just (s :: AttrSet t, p :: AttrSet SourcePos) ->
case M.lookup k s of
Just v -> do
traceM $ "Forcing value at selector " ++ Text.unpack k
force v $ case ks of
[] -> pure . Right
y:ys -> extract ?? (y:|ys)
Nothing ->
Left . (, path) <$> toValue (s, p)
Nothing ->
return $ Left (x, path)
evalSelector :: (MonadEval v m, FromValue (Text, DList Text) m v)
=> Bool -> NAttrPath (m v) -> m (NonEmpty Text)
evalSelector allowDynamic binds =
NE.map fst <$> traverse (evalGetterKeyName allowDynamic) binds
-- | Evaluate a component of an attribute path in a context where we are
-- *retrieving* a value
evalGetterKeyName :: (MonadEval v m, FromValue (Text, DList Text) m v)
=> Bool -> NKeyName (m v) -> m (Text, Maybe SourcePos)
evalGetterKeyName canBeDynamic
| canBeDynamic = evalKeyNameDynamicNotNull
| otherwise = evalKeyNameStatic
evalKeyNameStatic :: forall v m. MonadEval v m
=> NKeyName (m v) -> m (Text, Maybe SourcePos)
evalKeyNameStatic = \case
StaticKey k p -> pure (k, p)
DynamicKey _ ->
evalError @v "dynamic attribute not allowed in this context"
evalKeyNameDynamicNotNull
:: forall v m. (MonadEval v m, FromValue (Text, DList Text) m v)
=> NKeyName (m v) -> m (Text, Maybe SourcePos)
evalKeyNameDynamicNotNull = evalKeyNameDynamicNullable >=> \case
(Nothing, _) ->
evalError @v "value is null while a string was expected"
(Just k, p) -> pure (k, p)
-- | Evaluate a component of an attribute path in a context where we are
-- *binding* a value
evalSetterKeyName :: (MonadEval v m, FromValue (Text, DList Text) m v)
=> Bool -> NKeyName (m v) -> m (Maybe Text, Maybe SourcePos)
evalSetterKeyName canBeDynamic
| canBeDynamic = evalKeyNameDynamicNullable
| otherwise = fmap (first Just) . evalKeyNameStatic
-- | Returns Nothing iff the key value is null
evalKeyNameDynamicNullable
:: forall v m. (MonadEval v m, FromValue (Text, DList Text) m v)
=> NKeyName (m v)
-> m (Maybe Text, Maybe SourcePos)
evalKeyNameDynamicNullable = \case
StaticKey k p -> pure (Just k, p)
DynamicKey k ->
runAntiquoted "\n" (fmap Just . assembleString) (>>= fromValueMay) k
<&> \case Just (t, _) -> (Just t, Nothing)
_ -> (Nothing, Nothing)
assembleString :: forall v m. (MonadEval v m, FromValue (Text, DList Text) m v)
=> NString (m v) -> m (Text, DList Text)
assembleString = \case
Indented _ parts -> fromParts parts
DoubleQuoted parts -> fromParts parts
where
go = runAntiquoted "\n" (pure . (, mempty)) (>>= fromValue)
fromParts parts = mconcat <$> mapM go parts
buildArgument :: forall e v t m. MonadNixEval e v t m
=> NExprF (m v) -> Params (m v) -> m v -> m (AttrSet t)
buildArgument e params arg = do
scope <- currentScopes @_ @t
case params of
Param name -> M.singleton name
<$> thunk (exprFContext e (withScopes scope arg))
ParamSet s isVariadic m ->
arg >>= fromValue >>= \args -> do
let inject = case m of
Nothing -> id
Just n -> M.insert n $ const $
thunk (exprFContext e (withScopes scope arg))
loebM (inject $ alignWithKey (assemble scope isVariadic)
args (M.fromList s))
where
assemble :: Scopes m t
-> Bool
-> Text
-> These t (Maybe (m v))
-> AttrSet t
-> m t
assemble scope isVariadic k = \case
That Nothing ->
const $ evalError @v $ "Missing value for parameter: " ++ show k
That (Just f) -> \args ->
thunk $ exprFContext e
$ withScopes scope
$ pushScope args f
This x | isVariadic -> const (pure x)
| otherwise ->
const $ evalError @v $ "Unexpected parameter: " ++ show k
These x _ -> const (pure x)
-----
framedEvalExpr :: Framed e m => (NExprF (m v) -> m v) -> NExprLoc -> m v
framedEvalExpr eval = adi (eval . annotated . getCompose) psi
where
psi k v = withExprContext v (k v)
-----
{-
streamValues :: MonadVar m => v -> Stream (EValueF m) m ()
streamValues = void . yields . fmap go
where
go (EThunk (Left v)) = streamValues v
go (EThunk v) = effect (streamValues <$> forceThunk v)
-}