On Nov 22, 2007 8:19 AM, Peter Verswyvelen
worksFine = if True then putStrLn "True" else putStrLn "False"
This is just an expression, the indentation is inconsequential.
worksNOT = do if True then putStrLn "True" else putStrLn "False"
The first line, "if True", sets the indentation level of the statements in the "do" to two spaces. So this is interpreted as worksNOT = do { if True ; then putStrLn "True" ; else putStrLn "False" } Which is of course illegal.
worksAgain = do if True then putStrLn "True" else putStrLn "False"
Here, the indentation level of the "do" is still two spaces, but then then and else are at a higher indent than that, so they are interpreted as part of the preceding expression. The rules are actually very simple. Luke