<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;"><span style="font-family: courier,monaco,monospace,sans-serif;">I don't understand this error message. Haskell appears not to understand that 1 is a Num.<br><br>Prelude> :t 1<br>1 :: (Num t) => t<br>Prelude> :t [1,2,3,4,5]<br>[1,2,3,4,5] :: (Num t) => [t]<br>Prelude> <br><br>Michael<br><br>===================<br><br>f :: [Int] -> IO [Int]</span><br style="font-family: courier,monaco,monospace,sans-serif;"><span style="font-family: courier,monaco,monospace,sans-serif;">f lst = do return lst</span><br style="font-family: courier,monaco,monospace,sans-serif;"><br style="font-family: courier,monaco,monospace,sans-serif;"><span style="font-family: courier,monaco,monospace,sans-serif;">main = do let lst = f [1,2,3,4,5]</span><br style="font-family: courier,monaco,monospace,sans-serif;"><span style="font-family:
courier,monaco,monospace,sans-serif;"> fmap (+1) lst</span><br style="font-family: courier,monaco,monospace,sans-serif;"><br>===============================<br><br>Prelude> :l test<br>[1 of 1] Compiling Main ( test.hs, interpreted )<br><br>test.hs:5:17:<br> No instance for (Num [Int])<br> arising from the literal `1' at test.hs:5:17<br> Possible fix: add an instance declaration for (Num [Int])<br> In the second argument of `(+)', namely `1'<br> In the first argument of `fmap', namely `(+ 1)'<br> In the expression: fmap (+ 1) lst<br>Failed, modules loaded: none.<br>Prelude> <br></td></tr></table><br>