haskell-jp / questions #79

quote を書いたところで解決できる変数が解決されず、splice 時まで遅延されるのはむしろ特殊な挙動

Local names, which are not in scope at splice locations, are actually evaluated when the quotation is processed.

>>> :set -XTemplateHaskell
>>> import 
>>> let e = () in $(unboundVarE $ mkName "e")
()

正確には、 [e| |] のなかで束縛されてない変数が自動で unboundVarE $ mkName “e” されるところが、です。

ここまでの話は，`v` が見えない状況で [e|v|] が unboundVarE $ mkName "v" 相当になるのは何故かという説明のつもりでしたが

lookupValueName は splice 時に与えられた名前を解決し、quote 中の変数は quote processing 時に名前を解決します

>>> let e = () in $(unboundVarE $ mkName "e")
()

pure x = Mealy $ \_ -> (x, pure x)
Mealy p >>= fq = Mealy $ \x -> let {(y, p') = p x; (z, q') = runMealy (fq y) x} in (z, p' >>= q')

ghc-options:
- -rtsopts
- -prof
- -fprof-auto

ghc: panic! (the 'impossible' happened)
  (GHC version 8.6.5 for x86_64-unknown-linux):
	lookupGlobal
  Failed to load interface for 'GHC.Integer.Type'
  Perhaps you haven't installed the "p_dyn" libraries for package 'integer-gmp'?
  Use -v to see a list of the files searched for.
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in ghc:Outputable
        pprPanic, called at compiler/typecheck/TcEnv.hs:132:32 in ghc:TcEnv

Please report this as a GHC bug:  

app = Mealy $ \(f, x) -> let (y, g) = f x in (y, ???)

newtype Switch a b c = Switch (Mealy a (b, Maybe c))