WIP

M  src/Nix/Builtins.hs
M  src/Nix/Expr/Shorthands.hs
M  src/Nix/Utils.hs
M  tests/ParserTests.hs
M  tests/PrettyParseTests.hs
M  tests/ReduceExprTests.hs

src/Nix/Builtins.hs

@@ -583,7 +583,7 @@ headNix :: forall e t f m. MonadNix e t f m => NValue t f m -> m (NValue t f m)
 headNix =
   maybe
     (throwError $ ErrorCall "builtins.head: empty list")
-    (pure)
+    pure
   . viaNonEmpty head <=< fromValue @[NValue t f m]
 
 tailNix :: forall e t f m. MonadNix e t f m => NValue t f m -> m (NValue t f m)

src/Nix/Expr/Shorthands.hs

@@ -8,6 +8,7 @@ module Nix.Expr.Shorthands where
 import           Data.Fix
 import           Nix.Atoms
 import           Nix.Expr.Types
+import           Nix.Utils
 
 -- * Basic expression builders
 
@@ -33,15 +34,17 @@ mkFloat = Fix . mkFloatF
 
 -- | Put a regular (double-quoted) string.
 mkStr :: Text -> NExpr
-mkStr = Fix . NStr . DoubleQuoted . \case
-  "" -> mempty
-  x  -> [Plain x]
+mkStr = Fix . NStr . DoubleQuoted .
+  whenText
+    mempty
+    (one . Plain)
 
 -- | Put an indented string.
 mkIndentedStr :: Int -> Text -> NExpr
-mkIndentedStr w = Fix . NStr . Indented w . \case
-  "" -> mempty
-  x  -> [Plain x]
+mkIndentedStr w = Fix . NStr . Indented w .
+  whenText
+    mempty
+    (one . Plain)
 
 -- | Put a path. Use @True@ if the path should be read from the environment, else use @False@.
 mkPath :: Bool -> FilePath -> NExpr
@@ -79,6 +82,7 @@ mkNot = mkOp NNot
 -- Language allows negate integers & floats.
 mkNeg :: NExpr -> NExpr
 mkNeg = mkOp NNeg
+infix 8 `mkNeg`
 
 -- | Put a binary operator.
 mkOp2 :: NBinaryOp -> NExpr -> NExpr -> NExpr
@@ -93,20 +97,34 @@ mkParamset params variadic = ParamSet params variadic mempty
 mkRecSet :: [Binding NExpr] -> NExpr
 mkRecSet = mkSet Recursive
 
+($#~#) = mkRecSet
+
 -- | Put a non-recursive set.
 --
 -- > { .. }
 mkNonRecSet :: [Binding NExpr] -> NExpr
 mkNonRecSet = mkSet NonRecursive
 
+($###) = mkNonRecSet
+
+
 -- | General set builder function.
 mkSet :: Recursivity -> [Binding NExpr] -> NExpr
 mkSet r = Fix . NSet r
 
+-- | Empty set.
+--
+-- Monoid. Use @//@ operation (shorthand $//) to extend the set.
+emptySet :: NExpr
+emptySet = mkNonRecSet mempty
+
 -- | Put a list.
 mkList :: [NExpr] -> NExpr
 mkList = Fix . NList
 
+emptyList :: NExpr
+emptyList = mkList mempty
+
 -- | Wrap in a @let@.
 --
 -- (Evaluate the second argument after introducing the bindings.)
@@ -162,26 +180,9 @@ mkIf e1 e2 = Fix . NIf e1 e2
 mkFunction :: Params NExpr -> NExpr -> NExpr
 mkFunction params = Fix . NAbs params
 
--- | Lambda function, analog of Haskell's @\\ x -> x@:
---
--- +---------------+-----------+
--- | Haskell       | Nix       |
--- +===============+===========+
--- | @x ==> expr @ | @x: expr@ |
--- +---------------+-----------+
-(==>) :: Params NExpr -> NExpr -> NExpr
-(==>) = mkFunction
-infixr 1 ==>
-
--- | Dot-reference into an attribute set: @attrSet.k@
-(@.) :: NExpr -> Text -> NExpr
-(@.) obj name = getRefOrDefault obj name Nothing
-infixl 2 @.
-
-
 -- | General dot-reference with optional alternative if the jey does not exist.
 getRefOrDefault :: NExpr -> VarName -> Maybe NExpr -> NExpr
-getRefOrDefault obj name alt = Fix $ NSelect obj (StaticKey name :| mempty) alt
+getRefOrDefault obj name alt = Fix $ NSelect obj (mkSelector name) alt
 
 -- ** Base functor builders for basic expressions builders *sic
 
@@ -293,55 +294,116 @@ recAttrsE pairs = mkRecSet $ uncurry ($=) <$> pairs
 
 -- * Nix binary operators
 
--- | Nix binary operator builder.
-mkBinop :: NBinaryOp -> NExpr -> NExpr -> NExpr
-mkBinop = mkOp2
-
 (@@), ($==), ($!=), ($<), ($<=), ($>), ($>=), ($&&), ($||), ($->), ($//), ($+), ($-), ($*), ($/), ($++)
   :: NExpr -> NExpr -> NExpr
+--  2021-07-10: NOTE: Probably the presedence of some operators is still needs to be tweaked.
+
+-- | Dot-reference into an attribute set: @attrSet.k@
+(@.) :: NExpr -> Text -> NExpr
+(@.) obj name = getRefOrDefault obj name Nothing
+infix 9 @.
+
+-- | Dot-reference into an attribute set with alternative if the key does not exist.
+--
+-- > s.x or y
+(@./) :: NExpr -> VarName -> NExpr -> NExpr
+(@./) obj name alt = getRefOrDefault obj name $ pure alt
+infix 9 @./
+
 -- | Function application (@' '@ in @f x@)
 (@@) = mkOp2 NApp
-infixl 1 @@
--- | Equality: @==@
-($==) = mkOp2 NEq
--- | Inequality: @!=@
-($!=) = mkOp2 NNEq
--- | Less than: @<@
-($<)  = mkOp2 NLt
--- | Less than OR equal: @<=@
-($<=) = mkOp2 NLte
+infixl 8 @@
+
+-- | List concatenation: @++@
+($++) = mkOp2 NConcat
+infixr 7 $++
+
+-- | Multiplication: @*@
+($*)  = mkOp2 NMult
+infixl 6 $*
+
+-- | Division: @/@
+($/)  = mkOp2 NDiv
+infixl 6 $/
+
+-- | Addition: @+@
+($+)  = mkOp2 NPlus
+infixl 5 $+
+
+-- | Subtraction: @-@
+($-)  = mkOp2 NMinus
+infixl 5 $-
+
+-- | Logical negation: @!e@
+($!) :: NExpr -> NExpr
+($!) = mkNot
+infix 5 $!
+
+-- | Extend/override the left attr set, with the right one: @//@
+($//) = mkOp2 NUpdate
+infixr 5 $//
+
 -- | Greater than: @>@
 ($>)  = mkOp2 NGt
+infix 4 $>
+
 -- | Greater than OR equal: @>=@
+infix 4 $>=
 ($>=) = mkOp2 NGte
+
+-- | Less than OR equal: @<=@
+($<=) = mkOp2 NLte
+infix 4 $<=
+
+-- | Less than: @<@
+($<)  = mkOp2 NLt
+infix 4 $<
+
+-- | Equality: @==@
+($==) = mkOp2 NEq
+infix 3 $==
+
+-- | Inequality: @!=@
+($!=) = mkOp2 NNEq
+infix 3 $!=
+
 -- | AND: @&&@
 ($&&) = mkOp2 NAnd
+infixl 2 $&&
+
 -- | OR: @||@
 ($||) = mkOp2 NOr
+infixl 2 $||
+
 -- | Logical implication: @->@
 ($->) = mkOp2 NImpl
--- | Extend/override the left attr set, with the right one: @//@
-($//) = mkOp2 NUpdate
--- | Addition: @+@
-($+)  = mkOp2 NPlus
--- | Subtraction: @-@
-($-)  = mkOp2 NMinus
--- | Multiplication: @*@
-($*)  = mkOp2 NMult
--- | Division: @/@
-($/)  = mkOp2 NDiv
--- | List concatenation: @++@
-($++) = mkOp2 NConcat
+infix 1 $->
 
+-- | Lambda function, analog of Haskell's @\\ x -> x@:
+--
+-- +---------------+-----------+
+-- | Haskell       | Nix       |
+-- +===============+===========+
+-- | @x ==> expr @ | @x: expr@ |
+-- +---------------+-----------+
+(==>) :: Params NExpr -> NExpr -> NExpr
+(==>) = mkFunction
+infixr 1 ==>
 
--- * Under deprecation
 
--- NOTE: Remove after 2023-07
--- | Put an unary operator.
-mkOper :: NUnaryOp -> NExpr -> NExpr
-mkOper op = Fix . NUnary op
+-- -- * Under deprecation
 
--- NOTE: Remove after 2023-07
--- | Put a binary operator.
-mkOper2 :: NBinaryOp -> NExpr -> NExpr -> NExpr
-mkOper2 op a = Fix . NBinary op a
+-- -- NOTE: Remove after 2023-07
+-- -- | Put an unary operator.
+-- mkOper :: NUnaryOp -> NExpr -> NExpr
+-- mkOper op = Fix . NUnary op
+
+-- -- NOTE: Remove after 2023-07
+-- -- | Put a binary operator.
+-- mkOper2 :: NBinaryOp -> NExpr -> NExpr -> NExpr
+-- mkOper2 op a = Fix . NBinary op a
+
+-- -- NOTE: Remove after 2023-07
+-- | Nix binary operator builder.
+-- mkBinop :: NBinaryOp -> NExpr -> NExpr -> NExpr
+-- mkBinop = mkOp2

src/Nix/Utils.hs

@@ -196,6 +196,14 @@ list e f l =
     (null l)
 {-# inline list #-}
 
+whenText
+  :: a -> (Text -> a) -> Text -> a
+whenText e f t =
+  bool
+    (f t)
+    e
+    (Text.null t)
+
 -- | Lambda analog of @maybe@ or @either@ for Free monad.
 free :: (a -> b) -> (f (Free f a) -> b) -> Free f a -> b
 free fP fF fr =