On 1 Apr 2013, at 01:21, Seth Lastname wrote:
> Note 2 says, "If the first token after a 'where' (say) is not indented more
> than the enclosing layout context, then the block must be empty, so empty
> braces are inserted."
>
> It seems that, in Note 2, the "first token" necessarily refers to a lexeme
> other than '{' (else it would not make sense),
Correct.
> in which case a '{n}' token will have been inserted after 'where' (in the
> example given in the note), yielding a nested context which is "not indented
> more than the enclosing layout context",
Yes, a "{n}" token has been inserted after the "where".
No, it does not yield an incorrectly nested context, because L is the function
that decides whether to add to the context.
Looking only at the three equations for L that deal with the pseudo-token
"{n}", including their side conditions, we see:
L ({n} : ts) (m : ms) = { : (L ts (n : m : ms)) if n > m (Note 1)
L ({n} : ts) [] = { : (L ts [n]) if n > 0 (Note 1)
L ({n} : ts) ms = { : } : (L (< n >: ts) ms) (Note 2)
So, the third clause is triggered either when the nested-context stack (ms) is
empty and n is zero or negative; or when the context stack is non-empty and
n<m. That is, we avoid creating a context stack that would be incorrect
(according to Note 1).
Regards,
Malcolm
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