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POParsing date and time with FParsec
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copied!<p>Within a simple query language I'd like to recognize date and time literals, preferably without using delimiters. For example,</p> <pre><code>CreationDate = 2013-05-13 5:30 PM </code></pre> <p>I could use a combinator to detect the basic syntax (e.g., <code>yyyy-MM-dd hh:mm tt</code>), but then it needs to be passed to <code>DateTime.TryParse</code> for full validation. </p> <p>A few questions:</p> <ul> <li>Is there a combinator for "post processing" a parser result, e.g., <code>pstring "1/2/2000" |> (fun s -> try OK(DateTime.Parse s) with _ -> Fail("not a date"))</code></li> <li>Is it possible to apply a predicate to a string (as <code>satisfy</code> does to <code>char</code>)?</li> <li>Is there a better approach for parsing date/time?</li> </ul> <h3>UPDATE</h3> <p>Using Guvante's and Stephan's examples, I came up with this:</p> <pre><code>let dateTimeLiteral = let date sep = pipe5 pint32 sep pint32 sep pint32 (fun a _ b _ c -> a, b, c) let time = (pint32 .>>. (skipChar ':' >>. pint32)) .>>. (opt (stringCIReturn " am" false <|> stringCIReturn " pm" true)) (date (pstring "/") <|> date (pstring "-")) .>>. (opt (skipChar ' ' >>. time)) .>> ws >>=? (fun ((a, b, c), tt) -> let y, m, d = if a > 12 then a, b, c else c, a, b let h, n = match tt with | Some((h, n), tt) -> match tt with | Some true -> (match h with 12 -> h | _ -> h + 12), n | Some false -> (match h with 12 -> h - 12 | _ -> h), n | None -> h, n | None -> 0, 0 try preturn (System.DateTime(y, m, d, h, n, 0)) |>> DateTime with _ -> fail "Invalid date/time format") </code></pre>

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