sugar for data and other improvements

- parse types in let (everything but parser was there)
- add sugar for `data`
- move `joinBy` to prelude
- fix highlighting for char in vscode
- better errors for missing imports

port/Prettier.newt

@@ -14,7 +14,7 @@ import Prelude
 data Doc : U where
   Empty Line : Doc
   Text : String -> Doc
-  Nest : Nat -> Doc -> Doc
+  Nest : Int -> Doc -> Doc
   Seq : Doc -> Doc -> Doc
   Alt : Doc -> Doc -> Doc
 
@@ -24,7 +24,7 @@ data Doc : U where
 -- data Item = TEXT String | LINE Nat
 data Item : U where
   TEXT :  String -> Item
-  LINE : Nat -> Item
+  LINE : Int -> Item
 
 empty : Doc
 empty = Empty
@@ -43,13 +43,13 @@ group x = Alt (flatten x) x
 -- TODO - we can accumulate snoc and cat all at once
 layout : List Item -> SnocList String -> String
 layout Nil acc = fastConcat $ acc <>> Nil
-layout (LINE k :: x) acc = layout x (acc :< "\n" :< replicate k ' ')
+layout (LINE k :: x) acc = layout x (acc :< "\n" :< replicate (cast k) ' ')
 layout (TEXT str :: x) acc = layout x (acc :< str)
 
 -- Whether a documents first line fits.
-fits : Nat -> List Item -> Bool
+fits : Int -> List Item -> Bool
 fits 0 x = False
-fits w ((TEXT s) :: xs) = fits (w - length s) xs
+fits w ((TEXT s) :: xs) = fits (w - slen s) xs
 fits w _ = True
 
 -- vs Wadler, we're collecting the left side as a SnocList to prevent
@@ -58,21 +58,21 @@ fits w _ = True
 
 -- I've now added a `fit` boolean to indicate if we should cut when we hit the line length
 -- Wadler was relying on laziness to stop the first branch before LINE if necessary
-be : Bool -> SnocList Item -> Nat -> Nat -> List (Nat × Doc) -> Maybe (List Item)
+be : Bool -> SnocList Item -> Int -> Int -> List (Int × Doc) -> Maybe (List Item)
 be fit acc w k Nil = Just (acc <>> Nil)
 be fit acc w k ((i, Empty) :: xs) = be fit acc w k xs
 be fit acc w k ((i, Line) :: xs) = (be False (acc :< LINE i) w i xs)
 be fit acc w k ((i, (Text s)) :: xs) =
-  case not fit || (k + length s < w) of
-    True => (be fit (acc :< TEXT s) w (k + length s) xs)
+  case not fit || (k + slen s < w) of
+    True => (be fit (acc :< TEXT s) w (k + slen s) xs)
     False => Nothing
 be fit acc w k ((i, (Nest j x)) :: xs) = be fit acc w k ((i + j, x):: xs)
 be fit acc w k ((i, (Seq x y)) :: xs) = be fit acc w k ((i,x) :: (i,y) :: xs)
 be fit acc w k ((i, (Alt x y)) :: xs) =
   (_<>>_ acc) <$> (be True Lin w k ((i,x) :: xs) <|> be fit Lin w k ((i, y) :: xs))
 
-best : Nat -> Nat -> Doc -> List Item
-best w k x = fromMaybe Nil $ be False Lin w k ((Z,x) :: Nil)
+best : Int -> Int -> Doc -> List Item
+best w k x = fromMaybe Nil $ be False Lin w k ((0,x) :: Nil)
 
 -- interface Pretty a where
 --   pretty : a -> Doc
@@ -83,8 +83,8 @@ data Pretty : U -> U where
 pretty : {a} {{Pretty a}} → a → Doc
 pretty {{MkPretty p}} x = p x
 
-render : Nat -> Doc -> String
-render w x = layout (best w Z x) Lin
+render : Int -> Doc -> String
+render w x = layout (best w 0 x) Lin
 
 instance Semigroup Doc where
   x <+> y = Seq x (Seq (Text " ") y)
@@ -97,7 +97,7 @@ line = Line
 text : String -> Doc
 text = Text
 
-nest : Nat -> Doc -> Doc
+nest : Int -> Doc -> Doc
 nest = Nest
 
 instance Concat Doc where
@@ -123,7 +123,7 @@ stack = folddoc _</>_
 
 -- bracket x with l and r, indenting contents on new line
 bracket : String -> Doc -> String -> Doc
-bracket l x r = group (text l ++ nest (S (S Z)) (line ++ x) ++ line ++ text r)
+bracket l x r = group (text l ++ nest 2 (line ++ x) ++ line ++ text r)
 
 infixl 5 _<+/>_
 
@@ -138,7 +138,7 @@ fill Nil = Empty
 fill (x :: Nil) = x
 fill (x :: y :: xs) = Alt (flatten x <+> fill (flatten y :: xs)) (x </> fill (y :: xs))
 
--- separate with space
+-- separate with comma
 commaSep : List Doc -> Doc
 commaSep = folddoc (\a b => a ++ text "," <+/> b)