Malcolm Wallace wrote:
Out of interest, without trying it, what do you think this program
should print (the only difference between the 3 functions is the
indentation of the "where" line)?:
main = do print $ f1 1
print $ f2 1
print $ f3 1
I reckon it would be "layout error" at line 2. :-)
f1 x = x + case () of
() -> x
where x = 5
To be honest, it goes slightly against my intuition that the
pattern-match against () is accepted by the layout rule at all, because
it is indented further to the left than the case itself. Landin's
original rule was something like "everything strictly to the right and
below" belongs to the syntactic construct. This example breaks that
principle.
(hmm, in Ian's message it was lined up vertically with the 'case')
anyway, yes, it's a little weird but fine to get used to: the
layout-rule basically reacts to "of", "where", "let" and "do", and so it
can't even tell what a "beginning" of a construct is, like the word
'case'. ('where', for instance, comes after functions, 'class',
'instance', 'module'...). Nevertheless it (obviously?) needs to be more
indented than the enclosing layout-indentation.
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