leledumbo wrote:
consider this partial program:
if n>5 then
putStrLn "big"
else
putStrLn "small"
this works fine in hugs, but in ghc I must change it to:
if n>5
then
putStrLn "big"
else
putStrLn "small"
Actually both of those are valid expressions.
And they both work in hugs and ghc.
The question I imagine you're asking involves layout mode:
do
if n>5 then
putStrLn "big"
else
putStrLn "small"
this is shorthand for
do { if n > 5 then putStrLn "big" ; else putStrLn "small" }
which is a syntax error. A statement in a do block cannot begin with the
keyword "else".
If you indent the else a bit further than it counts and a continuation
of the enclosing expression (beginning with if) so it desugars to
do { if n > 5 then putStrLn "big" else putStrLn "small" }
which is fine.
Haskell' is apparently going to include a hack to permit this case. I
think that's a poor decision, because including a hack to the layout
rule makes it harder to understand and explain the layout rule.
Jules
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