/// <summary>
/// TryParse a single character matching 'predicate'
/// </summary>
/// <param name="predicate"></param>
/// <param name="description"></param>
/// <returns></returns>
public static Parser <char> Char(Predicate <char> predicate, string description)
{
if (predicate == null)
{
throw new ArgumentNullException("predicate");
}
if (description == null)
{
throw new ArgumentNullException("description");
}
return(i =>
{
if (!i.AtEnd)
{
if (predicate(i.Current))
{
return Result.Success(i.Current, i.Advance());
}
return Result.Failure <char>(i,
Observe.Error(string.Format("unexpected '{0}'", i.Current), description));
}
return Result.Failure <char>(i,
Observe.Error("Unexpected end of input reached", description));
});
}
/// <summary>
/// Refer to another parser indirectly. This allows circular compile-time dependency between parsers.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="reference"></param>
/// <returns></returns>
public static Parser <T> Ref <T>(Func <Parser <T> > reference)
{
if (reference == null)
{
throw new ArgumentNullException("reference");
}
Parser <T> p = null;
return(i =>
{
if (p == null)
{
p = reference();
}
if (i.Memos.ContainsKey(p))
{
throw new ParseException(i.Memos[p].ToString());
}
i.Memos[p] = Result.Failure <T>(i,
Observe.Error("Left recursion in the grammar."));
var result = p(i);
i.Memos[p] = result;
return result;
});
}
/// <summary>
/// Parse a stream of elements, attemting to skip over invalid elements.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="parser"></param>
/// <returns></returns>
/// <remarks>Implemented imperatively to decrease stack usage.</remarks>
public static Parser <IEnumerable <T> > ManyWithPanic <T, U>(this Parser <T> parser, Parser <U> panicUntil, string elementDescription)
{
if (parser == null)
{
throw new ArgumentNullException("parser");
}
if (panicUntil == null)
{
throw new ArgumentNullException("panicUntil");
}
return(i =>
{
var remainder = i;
var result = new List <T>();
var observations = new List <ResultObservation>();
var r = parser(i);
while (true)
{
if (r.WasSuccessful && remainder == r.Remainder)
{
break;
}
if (!r.WasSuccessful)
{
if (remainder == r.Remainder)
{
break;
}
observations.Add(Observe.Error("Unexpected {0}.", elementDescription));
remainder = r.Remainder;
var panicResult = panicUntil(remainder);
while (!panicResult.WasSuccessful && !remainder.AtEnd)
{
remainder = remainder.Advance();
panicResult = panicUntil(remainder);
}
remainder = panicResult.Remainder;
}
else
{
result.Add(r.Value);
remainder = r.Remainder;
}
r = parser(remainder);
}
return Result.Success <IEnumerable <T> >(result, remainder, observations);
});
}
/// <summary>
/// Parse end-of-input.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="parser"></param>
/// <returns></returns>
public static Parser <T> End <T>(this Parser <T> parser)
{
if (parser == null)
{
throw new ArgumentNullException("parser");
}
return(i => parser(i).IfSuccess(s =>
s.Remainder.AtEnd
? s
: Result.Failure <T>(s.Remainder,
Observe.Error(string.Format("unexpected '{0}'", s.Remainder.Current),
"end of input"))));
}
/// <summary>
/// Constructs a parser that will fail if the given parser succeeds,
/// and will succeed if the given parser fails. In any case, it won't
/// consume any input. It's like a negative look-ahead in regex.
/// </summary>
/// <typeparam name="T">The result type of the given parser</typeparam>
/// <param name="parser">The parser to wrap</param>
/// <returns>A parser that is the opposite of the given parser.</returns>
public static Parser <object> Not <T>(this Parser <T> parser)
{
if (parser == null)
{
throw new ArgumentNullException("parser");
}
return(i =>
{
var result = parser(i);
if (result.WasSuccessful)
{
var msg = string.Format("'{0}' was not expected", string.Join(", ", result.Observations.SelectMany(x => x.Expectations)));
return Result.Failure <object>(i, Observe.Error(msg));
}
return Result.Success <object>(null, i);
});
}
/// <summary>
/// Construct a parser from the given regular expression.
/// </summary>
/// <param name="regex">The regex expression.</param>
/// <param name="description">Description of characters that don't match.</param>
/// <returns>a parse of string</returns>
public static Parser <string> Regex(Regex regex, string description = null)
{
if (regex == null)
{
throw new ArgumentNullException("regex");
}
var expectations = description == null
? new string[0]
: new[] { description };
return(i =>
{
if (!i.AtEnd)
{
var remainder = i;
var input = i.Source.Substring(i.Position);
var match = regex.Match(input);
if (match.Success && match.Index == 0)
{
for (int j = 0; j < match.Length; j++)
{
remainder = remainder.Advance();
}
return Result.Success(match.Value, remainder);
}
var found = match.Index == input.Length
? "end of source"
: string.Format("`{0}'", input[match.Index]);
return Result.Failure <string>(
remainder,
Observe.Error("string matching regex `" + regex.ToString() + "' expected but " + found + " found", expectations));
}
return Result.Failure <string>(i,
Observe.Error("Unexpected end of input", expectations));
});
}
public static Parser <IEnumerable <T> > Repeat <T>(this Parser <T> parser, int count)
{
if (parser == null)
{
throw new ArgumentNullException("parser");
}
return(i =>
{
var remainder = i;
var result = new List <T>();
for (var n = 0; n < count; ++n)
{
var r = parser(remainder);
if (!r.WasSuccessful)
{
var what = r.Remainder.AtEnd
? "end of input"
: r.Remainder.Current.ToString();
var msg = string.Format("Unexpected '{0}'", what);
var exp = string.Format("'{0}' {1} times, but was {2}", string.Join(", ", r.Observations.SelectMany(x => x.Expectations)), count, n);
return Result.Failure <IEnumerable <T> >(i,
Observe.Error(msg, exp));
}
if (remainder != r.Remainder)
{
result.Add(r.Value);
}
remainder = r.Remainder;
}
return Result.Success <IEnumerable <T> >(result, remainder);
});
}
/// <summary>
/// Attempt parsing only if the <paramref name="except"/> parser fails.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <typeparam name="U"></typeparam>
/// <param name="parser"></param>
/// <param name="except"></param>
/// <returns></returns>
public static Parser <T> Except <T, U>(this Parser <T> parser, Parser <U> except)
{
if (parser == null)
{
throw new ArgumentNullException("parser");
}
if (except == null)
{
throw new ArgumentNullException("except");
}
// Could be more like: except.Then(s => s.Fail("..")).XOr(parser)
return(i =>
{
var r = except(i);
if (r.WasSuccessful)
{
return Result.Failure <T>(i,
Observe.Error("Excepted parser succeeded.", "other than the excepted input"));
}
return parser(i);
});
}
/// <summary>
/// Succeed if the parsed value matches predicate.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="parser"></param>
/// <param name="predicate"></param>
/// <returns></returns>
public static Parser <T> Where <T>(this Parser <T> parser, Func <T, bool> predicate)
{
if (parser == null)
{
throw new ArgumentNullException("parser");
}
if (predicate == null)
{
throw new ArgumentNullException("predicate");
}
return(i => parser(i).IfSuccess(s =>
predicate(s.Value) ? s : Result.Failure <T>(i,
Observe.Error(string.Format("Unexpected {0}.", s.Value)))));
}
/// <summary>
/// Names part of the grammar for help with error messages.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="parser"></param>
/// <param name="name"></param>
/// <returns></returns>
public static Parser <T> Named <T>(this Parser <T> parser, string name)
{
if (parser == null)
{
throw new ArgumentNullException("parser");
}
if (name == null)
{
throw new ArgumentNullException("name");
}
return(i => parser(i).IfFailure(f => f.Remainder == i ?
Result.Failure <T>(f.Remainder, f.Observations.Concat(new[] { Observe.Error(string.Format("Rule named '{0}' failed.", name)) })) :
f));
}
