copilot-prettyprinter: Preserve proposition quantifiers. Refs #254.

Currently, `copilot-language` remembers whether a proposition (i.e., a stream
of booleans) is quantified universally (i.e., using `forAll`) or existentially
(i.e., using `exists`). When translating from `copilot-language` to
`copilot-core`, however, the quantifier is discarded. This means that a
`copilot-core` `Property` does not record any quantifier information at all,
making it impossible for downstream libraries that use `copilot-core` to handle
universal quantification differently from existential quantification.

Now that `copilot-core` preserves quantifier information in its API, this
commit updates `copilot-prettyprinter` to pretty-print quantifier information
appropriately.

Author: RyanGlScott

copilot-prettyprinter/src/Copilot/PrettyPrint.hs

@@ -175,10 +175,15 @@ ppProperty :: Property -> Doc
 ppProperty
   Property
     { propertyName     = name
-    , propertyExpr     = e }
+    , propertyProp     = p }
   =   text "property \"" <> text name <> text "\""
   <+> text "="
-  <+> ppExpr e
+  <+> ppProp p
+
+-- | Pretty-print a Copilot proposition.
+ppProp :: Prop -> Doc
+ppProp (Forall e) = text "forall" <+> parens (ppExpr e)
+ppProp (Exists e) = text "exists" <+> parens (ppExpr e)
 
 -- | Pretty-print a Copilot specification, in the following order:
 --