Document Syntax.

src/Syntax.hs

@@ -2,9 +2,17 @@ module Syntax where
 
 import Data.Map
 
-data Syntax a f =
+-- | A node in an abstract syntax tree.
+data Syntax
+  a -- ^ The type of leaves in the syntax tree, typically String, but possibly some datatype representing different leaves more precisely.
+  f -- ^ The type representing another level of the tree, e.g. the children of branches. Often Cofree or Fix or similar.
+  =
+  -- | A terminal syntax node, e.g. an identifier, or atomic literal.
   Leaf a
+  -- | An ordered branch of child nodes, expected to be variadic in the grammar, e.g. a list of statements or uncurried function parameters.
   | Indexed [f]
+  -- | An ordered branch of child nodes, expected to be of fixed length in the grammar, e.g. a binary operator & its operands.
   | Fixed [f]
+  -- | A branch of child nodes indexed by some String identity. This is useful for identifying e.g. methods & properties in a class scope by their names. Note that comments can generally occur in these scopes as well; one strategy for dealing with this is to identify comments by their text in the source.
   | Keyed (Map String f)
   deriving (Functor, Show, Eq)