#2470: read for StdGen fails for arbitrary string
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Reporter: guest | Owner:
Type: bug | Status: closed
Priority: normal | Milestone:
Component: libraries/random | Version: 6.8.3
Severity: normal | Resolution: invalid
Keywords: StdGen read | Difficulty: Unknown
Testcase: | Architecture: x86
Os: Windows |
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Comment (by Isaac Dupree):
The Haskell 98 report is buggy; that behavior is unimplementable when
applying (`read::String->StdGen`) to an infinite list. Actually, no,
that's not quite right. (`readsPrec::Int->ReadS StdGen`) ==
(`readsPrec::Int->String->[(StdGen,String)]`). So readsPrec could be
defined to read only a finite amount of the string, and unconditionally
return `[(result,"")]` so that "read" always succeeded. But that breaks
the read/show identities (e.g. `(read.show)::[StdGen]->[StdGen]` would
break), and in general breaks the expected behavior for the `reads`
functions, so I don't think it's worth it to pretend the standard isn't
broken there.
-Isaac
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2470#comment:6>
GHC <http://www.haskell.org/ghc/>
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