Hmm....
> t_expr :: Parsec Object
> t_expr =
> (do comment_eol
> t_expr1 <- t_expr
> return t_expr1)
> <|>
> (do (tINITIAL_INDENT_NO_BANG <|> many1 hspace)
> (n_expr
> <|> do comment_eol
> t_expr2 <- t_expr
> return t_expr2))
> <|>
> (do tINITIAL_INDENT_WITH_BANG
> fail "cannot start with a bang!")
> <|>
> (do eof
> return $ generate_eof)
> <|>
> i_expr
Looks fine!
On 1/10/13, David A. Wheeler <dwhee...@dwheeler.com> wrote:
> The file "sweet.g" in the development branch is coming together as a
> reasonable BNF for sweet-expressions.
>
> I intend to post 1-2 productions at a time, for review and comment. Here's
> the first one, the top-level production that defines sweet-expressions.
> This production handles special cases (initial indents, blank lines that
> precede the sweet-expression, etc.), then calls the production i_expr
> ("indented expression") for normal cases.
>
> Comments?
>
> Feel free to look at the whole file, sweet.g in the develop branch, which
> defines some of the terminals and non-terminals, such as:
> * comment_eol: End-of-line, optionally preceded by a ";..." comment.
> * INITIAL_INDENT_NO_BANG: An initial indent without "!"
> * n_expr: Neoteric-expression
>
> For EOF handling, for now I'm assuming that the system will insert an extra
> EOL at the end of a non-empty file if there isn't one already.
>
> --- David A. Wheeler
>
> =============================
>
> // Top-level sweet-expression production, t_expr.
> // This production handles special cases, then in the normal case
> // drops to the i_expr production.
>
> // The rule for "indent processing disabled on initial top-level hspace"
> // is a very simple (and clever) BNF construction by Alan Manuel K. Gloria.
> // If there is an indent it simply reads a single n-expression and returns.
> // If there is more than one on an initially-indented line, the later
> // horizontal space will not have have been read, so this production will
> // fire again on the next invocation, doing the right thing.
>
> // Although "!" is an indent character, it's an error to use it at the
> // topmost level. The only reason to indent at the top is to disable
> // indent processing, for backwards compatibility. Detecting this as
> // an error should detect some mistakes.
>
> t_expr returns [Object v]
> : comment_eol t_expr1=t_expr {$v=$t_expr1.v;} /* Initial lcomment, retry
> */
> | (INITIAL_INDENT_NO_BANG | hspace+ )
> (n_expr {$v = $n_expr.v;} /* indent processing disabled */
> | comment_eol t_expr2=t_expr {$v=$t_expr2.v;} )
> | INITIAL_INDENT_WITH_BANG error
> | EOF {generate_eof();} /* End of file */
> | i_expr {$v = $i_expr.v;} /* Normal case */ ;
>
>
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