Well aa isn't returning a string. It's returning a function for
later evaluation which encapsulates the string. It's like
driving anywhere in California. You can't get there following
the road signs unless you've driven there once before. In this
case the road signs say "return a string" but the way to get
their is "return a string encapsulated in a function". The error
message ("you can't get there from here") is then straightforward.
-ljr
Andrew Coppin wrote:
aa :: String -> String
aa instr = do
putStrLn "abc"
putStrLn "abc"
return "Az"
>> Couldn't match expected type `[t]' against inferred type
`IO ()'
Any code that does any I/O must have a result type "IO blah". If the
code returns no useful information, it will be "IO ()". If, like above,
it returns a string, it will be "IO String". And so on.
(I must say, that error message doesn't make it terribly clear what the
problem is...)
--
Lanny Ripple <[EMAIL PROTECTED]>
ScmDB / Cisco Systems, Inc.
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