[GHC] #9843: Add flag to infer undefined for variables with only types

[GHC]

#9843: Add flag to infer undefined for variables with only types
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       Reporter:  tempay             |                   Owner:
           Type:  feature request    |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Compiler           |                 Version:  7.8.3
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
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 It would be convenient to be able to write only type declarations for some
 or all variables and have the compiler assume that the definitions of
 those variables are 'undefined'.

 For example:

 {{{#!hs
 functionOne :: x -> y
 functionTwo :: y -> z
 functionThree :: x -> y
 functionThree = functionOne . functionTwo
 }}}

 would be equivalent to

 {{{#!hs
 functionOne :: x -> y
 functionOne = undefined
 functionTwo :: y -> z
 functionTwo = undefined
 functionThree :: x -> y
 functionThree = functionOne . functionTwo
 }}}

 I feel this would make type-driven development significantly more
 convenient/clean.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9843>
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