doc/guide/src/WarnUnusedAnomalies.adoc

   1 WarnUnusedAnomalies
   2 ===================
   3
   4 The `warnUnused` <:MLBasisAnnotations:MLBasis annotation> can be used
   5 to report unused identifiers.  This can be useful for catching bugs
   6 and for code maintenance (e.g., eliminating dead code).  However, the
   7 `warnUnused` annotation can sometimes behave in counter-intuitive
   8 ways.  This page gives some of the anomalies that have been reported.
   9
  10 * Functions whose only uses are recursive uses within their bodies are
  11 not warned as unused:
  12 +
  13 [source,sml]
  14 ----
  15 local
  16 fun foo () = foo () : unit
  17 val bar = let fun baz () = baz () : unit in baz end
  18 in
  19 end
  20 ----
  21 +
  22 ----
  23 Warning: z.sml 3.5.
  24   Unused variable: bar.
  25 ----
  26
  27 * Components of actual functor argument that are necessary to match
  28 the functor argument signature but are unused in the body of the
  29 functor are warned as unused:
  30 +
  31 [source,sml]
  32 ----
  33 functor Warning (type t val x : t) = struct
  34    val y = x
  35 end
  36 structure X = Warning (type t = int val x = 1)
  37 ----
  38 +
  39 ----
  40 Warning: z.sml 4.29.
  41   Unused type: t.
  42 ----
  43
  44
  45 * No component of a functor result is warned as unused.  In the
  46 following, the only uses of `f2` are to match the functor argument
  47 signatures of `functor G` and `functor H` and there are no uses of
  48 `z`:
  49 +
  50 [source,sml]
  51 ----
  52 functor F(structure X : sig type t end) = struct
  53    type t = X.t
  54    fun f1 (_ : X.t) = ()
  55    fun f2 (_ : X.t) = ()
  56    val z = ()
  57 end
  58 functor G(structure Y : sig
  59                            type t
  60                            val f1 : t -> unit
  61                            val f2 : t -> unit
  62                            val z : unit
  63                         end) = struct
  64    fun g (x : Y.t) = Y.f1 x
  65 end
  66 functor H(structure Y : sig
  67                            type t
  68                            val f1 : t -> unit
  69                            val f2 : t -> unit
  70                            val z : unit
  71                         end) = struct
  72    fun h (x : Y.t) = Y.f1 x
  73 end
  74 functor Z() = struct
  75    structure S = F(structure X = struct type t = unit end)
  76    structure SG = G(structure Y = S)
  77    structure SH = H(structure Y = S)
  78 end
  79 structure U = Z()
  80 val _ = U.SG.g ()
  81 val _ = U.SH.h ()
  82 ----
  83 +
  84 ----
  85 ----