[Haskell-cafe] Parsec question (new user): unexpected end of input

[Peter Schmitz]

I am a new Parsec user, and having some trouble with a relatively
simple parser.

The grammar I want to parse contains tags (not html) marked by
angle brackets (e.g., "<some tag>"), with arbitrary text (no angle
brackets allowed) optionally in between tags.

Tags may not nest, but the input must begin and end with a tag.

Whitespace may occur anywhere (beginning/end of input,
inside/between tags, etc.), and is optional.

I think my problem may be a lack of using "try", but I'm not sure
where.

At runtime I get:

Error parsing file: "...\sampleTaggedContent.txt" (line 4, column 1):
unexpected end of input
expecting "<"

The input was:

<tag1>stuff<tag 2>
more stuff < tag 3 > even more
<lastTag>

The code is below. (I'm using Parsec-2.1.0.1.) I don't really want
to return anything meaningful yet; just parse okay.

Any advice about the error (or how to simplify or improve the code)
would be appreciated.

Thanks much,
-- Peter


> -- Parsers:
> taggedContent = do
>    optionalWhiteSpace
>    aTag
>    many tagOrContent
>    aTag
>    eof
>    return "Parse complete."
>
> tagOrContent = aTag <|> someContent <?> "tagOrContent"
>
> aTag = do
>    tagBegin
>    xs <- many (noneOf [tagEndChar])
>    tagEnd
>    optionalWhiteSpace
>    return ()
>
> someContent = do
>    manyTill anyChar tagBegin
>    return ()
>
> optionalWhiteSpace = spaces   -- i.e., any of " \v\f\t\r\n"
> tagBegin = char tagBeginChar
> tagEnd = char tagEndChar
>
> -- Etc:
> tagBeginChar = '<'
> tagEndChar = '>'

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