# 051: contextorder2.hs
[↑up](bunny_notes)

- issued: 2020-04-28
- 分類： A サンプルコードが fail
- status: Open

## 概要

instance 宣言における型変数の出現順序に関するもの。以下のプログラムがエラーとなる：

$$<pre>{
data Pair a b = Pair a b

instance (Show a, Show b) => Show (Pair b a) where
  show (Pair x y) = "Pair " ++ show x ++ " " ++ show y

main = print (Pair 1 'x')
$$}

## 調査ログ
## 2020-12-17

bunny 0.9.0 での実行結果：

$$<pre>{
$ bunny testrun contextorder2.hs
/home/unno/bunny/0.9.0/bin/bunnyc -d ./jout/contextorder2 --xno-implicit-prelude /home/unno/bunny/0.9.0/lib/Prelude.hs
/home/unno/bunny/0.9.0/bin/bunnyc -d ./jout/contextorder2 --xlibrary-path /home/unno/bunny/0.9.0/lib contextorder2.hs
Not a BoxedCharObj:AtomExpr(a=Var(obj=1 :: Integer))
Exception in thread "main" java.lang.AssertionError
        at jp.ne.sakura.uhideyuki.brt.runtime.RTLib.toJString(RTLib.java:98)
        at jp.ne.sakura.uhideyuki.brt.runtime.PutStrLnFunc.call(RTLib.java:29)
        at jp.ne.sakura.uhideyuki.brt.runtime.EvalApply.evalFun(RT.java:243)
        at jp.ne.sakura.uhideyuki.brt.runtime.EvalApply.runStep(RT.java:60)
        at jp.ne.sakura.uhideyuki.brt.runtime.EvalApply.eval(RT.java:18)
        at jp.ne.sakura.uhideyuki.brt.runtime.RT.eval(RT.java:292)
        at Sample.main(Sample.java:6)
$$}

### 2021-01-13

$<verb>{--ddump-core} してみる。

Pair 向け Show の実体では、辞書を a, b の順番でうけとって、つかうのは b, a 
順となっている：

$$<pre>{
(Main.Pair%I.show :: ([Prelude.Show t64,Prelude.Show t65] :=> (((Main.Pair t65) t64) -> [Prelude.Char]))) =
    \(Main.Pair%I.show.DARG0 :: Ä) (Main.Pair%I.show.DARG1 :: Ä) ->
        \(_Main.Pair%I.show.U1 :: ([Prelude.Show t50,Prelude.Show t51] :=> ((Main.Pair t51) t50))) ->
            case (_Main.Pair%I.show.U1 :: ([Prelude.Show t50,Prelude.Show t51] :=> ((Main.Pair t51) t50))) (_Main.Pair%I.show.U1b :: ([Prelude.Show t50,Prelude.Show t51] :=> ((Main.Pair t51) t50))) of
                Main.Pair (_Main.Pair%I.show.U2 :: t52) (_Main.Pair%I.show.U3 :: t53) :: (t52 -> (t53 -> ((Main.Pair t52) t53))) ->
                    (((Prelude.++ :: ([t55] -> ([t55] -> [t55])))
                        "Pair ")
                      (((Prelude.++ :: ([t56] -> ([t56] -> [t56])))
                          (((Prelude.show :: ([Prelude.Show t57] :=> (t57 -> [Prelude.Char])))
                              (Main.Pair%I.show.DARG1 :: Å))
                            (_Main.Pair%I.show.U2 :: t52)))
                        (((Prelude.++ :: ([t60] -> ([t60] -> [t60])))
                            " ")
                          (((Prelude.show :: ([Prelude.Show t61] :=> (t61 -> [Prelude.Char])))
                              (Main.Pair%I.show.DARG0 :: Å))
                            (_Main.Pair%I.show.U3 :: t53)))))

$$}

一方、渡す側では Pair に渡す順番で CompositDict を構成している：

$$<pre>{
(Main.main :: (Prelude.IO Prelude.())) =
    (((Prelude.print :: ([Prelude.Show t1] :=> (t1 -> (Prelude.IO Prelude.()))))
        (CompositDict ${Main.Pair Prelude.Show} [${Prelude.Integer Prelude.Show},${Prelude.Char Prelude.Show}]))
      (((Main.Pair :: (t2 -> (t3 -> ((Main.Pair t2) t3))))
          (((Prelude.fromInteger :: ([Prelude.Num t4] :=> (Prelude.Integer -> t4)))
              ${Prelude.Integer Prelude.Num})
            (1 :: Prelude.Integer)))  'x'))
$$}

これ、Rename の段階で $<verb>{instance (Show a, Show b) => Show (Pair b a) where}
を $<verb>{instance (Show b, Show a) => Show (Pair b a) where}
に書き換えてやれば、つじつまが合うんじゃないかな。

## 2021-10-24

全件確認シリーズ：

$$<pre>{
unno@unno-FMVD70GN7G ~/work/bissues/051 
$ cat contextorder2.hs 
data Pair a b = Pair a b

instance (Show a, Show b) => Show (Pair b a) where
  show (Pair x y) = "Pair " ++ show x ++ " " ++ show y

main = print (Pair 1 'x')
unno@unno-FMVD70GN7G ~/work/bissues/051 
$ runhaskell contextorder2.hs 
Pair 1 'x'
unno@unno-FMVD70GN7G ~/work/bissues/051 
$ ~/prj/bunny/compiler/bin/bunny testrun contextorder2.hs 
/home/unno/prj/bunny/compiler/bin/bunnyc -d ./jout/contextorder2 --xno-implicit-prelude /home/unno/prj/bunny/compiler/bin/../lib/Prelude.hs
/home/unno/prj/bunny/compiler/bin/bunnyc -d ./jout/contextorder2 --xlibrary-path /home/unno/prj/bunny/compiler/bin/../lib contextorder2.hs
Not a BoxedCharObj:AtomExpr(a=Var(obj=1 :: Integer))
Exception in thread "main" java.lang.AssertionError
        at jp.ne.sakura.uhideyuki.brt.runtime.RTLib.toJString(RTLib.java:98)
        at jp.ne.sakura.uhideyuki.brt.runtime.PutStrLnFunc.call(RTLib.java:29)
        at jp.ne.sakura.uhideyuki.brt.runtime.EvalApply.evalFun(RT.java:243)
        at jp.ne.sakura.uhideyuki.brt.runtime.EvalApply.runStep(RT.java:60)
        at jp.ne.sakura.uhideyuki.brt.runtime.EvalApply.eval(RT.java:18)
        at jp.ne.sakura.uhideyuki.brt.runtime.RT.eval(RT.java:292)
        at Sample.main(Sample.java:6)
$$}

ランタイムエラーになっているよう。