flag to define transpose [] == _|_

I use transpose a lot as an "unzip" function for lists. For example, suppose:

foo :: [[String]]

is a list of rows (say, of lenght 2) obtained from a SQL query. To transform it into a list of 2 columns, I simply write transpose foo. But, if foo is empty, I obtain... [[],[]]? No, I obtain []. I want the program to raise an error and stop, instead of (perhaps) produce a pattern match failure later, because transpose [] can arguably be [[]] or [[],[]] or [[],[],[]] or ... at least in some situations where it is used to "unzip" lists of lists.

I could use foo :: [(String, String)] or foo :: [(String, String, String)] etc., but [ [String]] is simpler and more general, and I can use map, etc.

Trac metadata

Trac field	Value
Version	6.6.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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Operating system	Unknown
Architecture	Unknown