| Oh ye Haskell wizards. Is the following program syntactically legal
| or not?
|
| x = let a = let { b=1;
| c=2
| } in 3
| in 4
|
| I.e. is the layout rule from an outer scope in effect even inside
| explicit brackets?
Obviously, this needs clarification. There would seem to be three
possibilities:
1) Layout from an outer scope applies even within explicit
brackets.
2) Layout can be used in a nested scope inside explicit brackets,
but indentations from outside the brackets do not apply.
3) Layout is never in effect within explicit brackets.
I favor (3) for its simplicity, although (2) is also sensible. (1)
seems like a bad idea.
| Here's another
|
| x = let a = let
| in 3
| in 4
|
| OK, what happens? First we insert an lcurl after the first let and
| remember the indentation (8). Then the second let will get an lcurl
| at indentation 3 (position of in). But 3 is less than 8 so there also be
| an rcurl from the first let. The last in will have an rcurl inserted because
| otherwise we would have a syntax error. So we get
|
| x = let { a = let
| {}in 3
| }in 4
|
| This is a correct program, but the curls in the empty let were not inserted
| by matching constructs!!
|
|
| -- Lennart & Niklas
I think this could be clarified by a slight rewording of the layout rules:
Rather than saying that a layout indentation is established by the first
token other than { following one of the herald keywords, say that anywhere
the grammar has
{ decls }
a layout indentation is established by the first token of decls , if any,
in the absence of a preceding {. Thus, in the above example, there is no
layout for the inner let. Of course, this rule is no longer purely lexical,
but that is the case with inserted }s anyway.
--Joe
