1 module Language.Symantic.CLI.Fixity where
4 import Data.Eq (Eq(..))
5 import Data.Function ((.))
7 import Data.Maybe (Maybe(..))
8 import Data.Ord (Ord(..))
9 import Text.Show (Show(..))
10 import qualified Data.Bool as Bool
20 = Prefix { unifix_prece :: Precedence }
21 | Postfix { unifix_prece :: Precedence }
27 { infix_assoc :: Maybe Associativity
28 , infix_prece :: Precedence
31 infixL :: Precedence -> Infix
32 infixL = Infix (Just AssocL)
34 infixR :: Precedence -> Infix
35 infixR = Infix (Just AssocR)
37 infixB :: Side -> Precedence -> Infix
38 infixB = Infix . Just . AssocB
40 infixN :: Precedence -> Infix
41 infixN = Infix Nothing
49 -- | Given 'Precedence' and 'Associativity' of its parent operator,
50 -- and the operand 'Side' it is in,
51 -- return whether an 'Infix' operator
52 -- needs to be enclosed by parenthesis.
53 needsParenInfix :: (Infix, Side) -> Infix -> Bool
54 needsParenInfix (po, lr) op =
55 infix_prece op < infix_prece po
56 || infix_prece op == infix_prece po
60 case (lr, infix_assoc po) of
61 (_, Just AssocB{}) -> True
62 (SideL, Just AssocL) -> True
63 (SideR, Just AssocR) -> True
66 -- * Type 'Precedence'
69 -- ** Class 'PrecedenceOf'
70 class PrecedenceOf a where
71 precedence :: a -> Precedence
72 instance PrecedenceOf Fixity where
73 precedence (Fixity1 uni) = precedence uni
74 precedence (Fixity2 inf) = precedence inf
75 instance PrecedenceOf Unifix where
76 precedence = unifix_prece
77 instance PrecedenceOf Infix where
78 precedence = infix_prece
80 -- * Type 'Associativity'
82 = AssocL -- ^ Associate to the left: @a ¹ b ² c == (a ¹ b) ² c@
83 | AssocR -- ^ Associate to the right: @a ¹ b ² c == a ¹ (b ² c)@
84 | AssocB Side -- ^ Associate to both sides, but to 'Side' when reading.