Am Montag, 6. März 2006 12:30 schrieb Malcolm Wallace:
Brian Hulley wrote:
However I think there is an error in the description of this in section 2.7 of the Haskell98 report, which states:
"If the indentation of the non-brace lexeme immediately following a where, let, do or of is less than or equal to the current indentation level, then instead of starting a layout, an empty list "{}" is inserted, and layout processing occurs for the current level ..."
I dispute the "or equal" in the above statement, since it seems to be clearly in contradiction to what is actually being done.
Section 2.7 does say that it is an informal description, so although it is correct, it is not complete. In the case of the module header, the question is really "what is the current indentation level?" (that we must be strictly greater than). The answer can be found in the formal definition of the layout rule in section 9.3. At the beginning of the module, there is _no_ current indentation level - thus the fourth equation of L applies.
Regards, Malcolm
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) []. Another thing that irritates me: in section 9.5, we have the production 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 } ? Cheers, Daniel -- "In My Egotistical Opinion, most people's C programs should be indented six feet downward and covered with dirt." -- Blair P. Houghton