add comments, fix fc on an error, add constructor for U

src/Lib/Elab.idr

@@ -889,11 +889,9 @@ buildCase ctx prob scnm scty (dcName, arity, ty) = do
 
     makeConstr : List Bind -> List Pattern -> M (List (String, Pattern))
     makeConstr [] [] = pure $ []
-    -- would need M in here to throw, and I'm building stuff as I go, I suppose I could <$>
-    makeConstr [] (pat :: pats) = error ctx.ctxFC "too many patterns"
+    makeConstr [] (pat :: pats) = error (getFC pat) "too many patterns"
     makeConstr ((MkBind nm Implicit x) :: xs) [] = pure $ (nm, PatWild emptyFC Implicit) :: !(makeConstr xs [])
     makeConstr ((MkBind nm Auto x) :: xs) [] = pure $ (nm, PatWild emptyFC Auto) :: !(makeConstr xs [])
-    -- FIXME need a proper error, but requires wiring M three levels down
     makeConstr ((MkBind nm Explicit x) :: xs) [] = error ctx.ctxFC "not enough patterns"
     makeConstr ((MkBind nm Explicit x) :: xs) (pat :: pats) =
       if getIcit pat == Explicit

src/Main.idr

@@ -55,8 +55,9 @@ writeSource fn = do
   docs <- compile
   let src = unlines $
         [ "\"use strict\";"
-        ,  "const PiType = (h0, h1) => ({ tag: \"PiType\", h0, h1 })" ]
-        ++ map (render 90) docs
+        , "const PiType = (h0, h1) => ({ tag: \"PiType\", h0, h1 })"
+        , "const U = { tag: \"U\" };"
+        ] ++ map (render 90) docs
   Right _ <- writeFile fn src
     | Left err => fail (show err)
   Right _ <- chmodRaw fn 493 | Left err => fail (show err)