Daniel Fischer
At the beginning of the module, there is _no_ current indentation level - thus the fourth equation of L applies.
I think, the third from last equation of L applies, since "If the first lexeme of a module is _not_ { or module, then it is preceded by {n} where n is the indentation of the lexeme.", so we start L with L ('module':ts) [].
Indeed, and thus, when we get to the end of the first 'where' token, the stack of indentation contexts is still empty. Hence my remark about the fourth equation.
body -> { impdecls; topdecls } | { impdecls } | { topdecls }
The first line seems to suggest that import declaraions were admissible also after topdecls, but any attempt to place an impdecl after a topdecl leads --fortunately-- to a parse error in hugs and ghc, shouldn't the production be
body -> { impdecls }; { topdecls } ?
I think you have mis-read the brace characters as if they were the EBNF meta symbols for repetition. They do in fact mean the literal brace symbol, which may be explicitly present in the source, or inserted by the layout rule. Thus, topdecls must follow impdecls, and be at the same indentation level if layout matters. Regards, Malcolm