don't print empty contexts in errors

lib/Quox/Context.idr

@@ -218,7 +218,7 @@ unzip3 (tel :< (x, y, z)) =
 
 
 
-export
+public export
 lengthPrf : Telescope _ from to -> (len ** len + from = to)
 lengthPrf [<]        = (0 ** Refl)
 lengthPrf (tel :< _) =
@@ -234,6 +234,11 @@ public export %inline
 length : Telescope {} -> Nat
 length = fst . lengthPrf
 
+public export
+null : Telescope _ from to -> Bool
+null [<] = True
+null _   = False
+
 
 export
 foldl : {0 acc : Nat -> Type} ->

lib/Quox/Typing/Context.idr

@@ -71,6 +71,10 @@ namespace TyContext
   empty =
     MkTyContext {dctx = new, dnames = [<], tctx = [<], tnames = [<], qtys = [<]}
 
+  public export %inline
+  null : TyContext q d n -> Bool
+  null ctx = null ctx.dnames && null ctx.tnames
+
   export %inline
   extendTyN : Telescope (\n => (q, BaseName, Term q d n)) from to ->
               TyContext q d from -> TyContext q d to
@@ -158,6 +162,10 @@ namespace EqContext
     dassign = [<], dnames = [<], tctx = [<], tnames = [<], qtys = [<]
   }
 
+  public export %inline
+  null : EqContext q n -> Bool
+  null ctx = null ctx.dnames && null ctx.tnames
+
   export %inline
   extendTyN : Telescope (\n => (q, BaseName, Term q 0 n)) from to ->
               EqContext q from -> EqContext q to

lib/Quox/Typing/Error.idr

@@ -300,12 +300,12 @@ parameters {auto _ : (Eq q, IsQty q, PrettyHL q)} (unicode : Bool)
   where
     inTContext : TyContext q d n -> Doc HL -> Doc HL
     inTContext ctx doc =
-      if showContext then
+      if showContext && not (null ctx) then
         vsep [sep ["in context", prettyTyContext unicode ctx], doc]
       else doc
 
     inEContext : EqContext q n -> Doc HL -> Doc HL
     inEContext ctx doc =
-      if showContext then
+      if showContext && not (null ctx) then
         vsep [sep ["in context", prettyEqContext unicode ctx], doc]
       else doc