Tab "\t" character behaviour in (Win)Hugs/ghc

[Rijk-Jan van Haaften]

Hello,

Recently, Craig Delehanty discovered that there is
a difference in behaviour of putStr "a\tb" between
Hugs and WinHugs (see comp.lang.functional).

Hugs interprets it as a alignment character:
 >putStr "a\tb"
"a       b"
 >
(7 spaces)
but in WinHugs, it is always the same as 8 spaces:
 >putStr "a\tb"
"a        b"
 >
(8 spaces)

What does the language definition say about this?
What is the behaviour of ghc/ghci?

Rijk-Jan