Add flag to infer undefined for variables with only types

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:

functionOne :: x -> y
functionTwo :: y -> z
functionThree :: x -> y
functionThree = functionOne . functionTwo

would be equivalent to

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.

Trac metadata

Trac field	Value
Version	7.8.3
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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