Today i wrote some sample code after a Logic lecture at my university. The idea is to represent the AST of propositional logic as an ADT with some convenience functions (like read-/show instances) and then later perhaps try to make some automatic transformations on the AST. After construction of the Show instances i found the output a bit boring and thought that some Unicode math symbols would spice things up. What happens can be seen in the attached picture (only 3k, that's ok right?). My terminal supports UTF-8 (when i do cat Logic.hs i can see the unicode symbols properly). What might be the problem?
regards Mattias
module Logic where
infixr 5 :->:, :/\:, :\/:
infixr 5 -->, /\, \/
infix 4 :|-:, :|=:
infix 4 |-, |=
data Logic = Formulae :|-: Formulae
| Formulae :|=: Formulae
data Formulae = Formulae :->: Formulae
| Formulae :/\: Formulae
| Formulae :\/: Formulae
| Formulae :<->: Formulae
| Not Formulae
| P
| Q
| R
| S
-- Operators
(-->) = (:->:)
(/\) = (:/\:)
(\/) = (:\/:)
(<->) = (:<->:)
(|-) = (:|-:)
(|=) = (:|=:)
--a <-> b = (a --> b) /\ (b --> a)
-- Show
instance Show Logic where
showsPrec d (f1 :|-: f2) = shows f1 . showString " ⊢ " . shows f2
showsPrec d (f1 :|=: f2) = shows f1 . showString " ⊨ " . shows f2
p = 5
p' = 6
instance Show Formulae where
showsPrec d (f1 :->: f2) = showBinaryF d f1 " → " f2
showsPrec d (f1 :/\: f2) = showBinaryF d f1 " ⋀ " f2
showsPrec d (f1 :\/: f2) = showBinaryF d f1 " ⋁ " f2
showsPrec d (f1 :<->: f2) = showBinaryF d f1 " ↔ " f2
showsPrec d (Not f) = showString "¬"
. showsPrec p' f
showsPrec _ P = showString "p"
showsPrec _ Q = showString "q"
showsPrec _ R = showString "r"
showsPrec _ S = showString "s"
showBinaryF d f1 op f2 = showParen (d > p)
$ showsPrec p' f1
. showString op
. showsPrec p' f2
import Logic main = do print (P --> Q |- (Not P) --> (Not Q))
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