Parser0[A] attempts to extract an A value from the given input,
potentially moving its offset forward in the process.
Parser0[A] attempts to extract an A value from the given input,
potentially moving its offset forward in the process.
When calling parse, one of three outcomes occurs:
-
Success: The parser consumes zero-or-more characters of input and successfully extracts a value. The input offset will be moved forward by the number of characters consumed.
-
Epsilon failure: The parser fails to extract a value without consuming any characters of input. The input offset will not be changed.
-
Arresting failure: The parser fails to extract a value but does consume one-or-more characters of input. The input offset will be moved forward by the number of characters consumed and all parsing will stop (unless a higher-level parser backtracks).
Operations such as x.orElse(y) will only consider parser y if
x returns an epsilon failure; these methods cannot recover from
an arresting failure. Arresting failures can be "rewound" using
methods such as x.backtrack (which converts arresting failures
from x into epsilon failures), or softProduct(x, y) (which can
rewind successful parses by x that are followed by epsilon
failures for y).
Rewinding tends to make error reporting more difficult and can lead to exponential parser behavior it is not the default behavior.
- Companion
- object
Value members
Concrete methods
Compose two parsers, ignoring the values extracted by the left-hand parser.
Compose two parsers, ignoring the values extracted by the left-hand parser.
x *> y is equivalent to (x.void ~ y).map(_._2).
Compose two parsers, ignoring the values extracted by the right-hand parser.
Compose two parsers, ignoring the values extracted by the right-hand parser.
x <* y is equivalent to (x ~ y.void).map(_._1).
Convert epsilon failures into None values.
Convert epsilon failures into None values.
Normally if a parser fails to consume any input it fails with an
epsilon failure. The ? method converts these failures into
None values (and wraps other values in Some(_)).
If the underlying parser failed with other errors, this parser will still fail.
If this parser fails to match, rewind the offset to the starting point before moving on to other parser.
If this parser fails to match, rewind the offset to the starting point before moving on to other parser.
This method converts arresting failures into epsilon failures, which includes rewinding the offset to that used before parsing began.
This method will most often be used before calling methods such
as orElse, ~, or flatMap which involve a subsequent parser
picking up where this one left off.
Use this parser to parse between values.
Use this parser to parse between values.
Parses b followed by this and c.
Returns only the values extracted by this parser.
Transform parsed values using the given function, or fail when not defined
Transform parsed values using the given function, or fail when not defined
When the function is not defined, this parser fails This is implemented with select, which makes it more efficient than using flatMap
If this parser fails to parse its input with an epsilon error, try the given parser instead.
If this parser fails to parse its input with an epsilon error, try the given parser instead.
If this parser fails with an arresting error, the next parser won't be tried.
Backtracking may be used on the left parser to allow the right one to pick up after any error, resetting any state that was modified by the left parser.
This method is similar to Parser#orElse but returns Either.
If the predicate is not true, fail you may want .filter(fn).backtrack so if the filter fn fails you can fall through in an oneOf0 or orElse
If the predicate is not true, fail you may want .filter(fn).backtrack so if the filter fn fails you can fall through in an oneOf0 or orElse
Without the backtrack, a failure of the function will be an arresting failure.
Dynamically construct the next parser based on the previously parsed value.
Dynamically construct the next parser based on the previously parsed value.
Using flatMap is very expensive. When possible, you should
prefer to use methods such as ~, *>, or <* when possible,
since these are much more efficient.
Transform parsed values using the given function.
Transform parsed values using the given function.
This parser will match the same inputs as the underlying parser,
using the given function f to transform the values the
underlying parser produces.
If the underlying value is ignored (e.g. map(_ => ...)) calling
void before map will improve the efficiency of the parser.
Transform parsed values using the given function, or fail on None
Transform parsed values using the given function, or fail on None
When the function return None, this parser fails This is implemented with select, which makes it more efficient than using flatMap
If this parser fails to parse its input with an epsilon error, try the given parser instead.
If this parser fails to parse its input with an epsilon error, try the given parser instead.
If this parser fails with an arresting error, the next parser won't be tried.
Backtracking may be used on the left parser to allow the right one to pick up after any error, resetting any state that was modified by the left parser.
Attempt to parse an A value out of str.
Attempt to parse an A value out of str.
This method will either return a failure, or else the remaining string and the parsed value.
To require the entire input to be consumed, see parseAll.
Attempt to parse all of the input str into an A value.
Attempt to parse all of the input str into an A value.
This method will return a failure unless all of str is consumed
during parsing.
p.parseAll(s) is equivalent to (p <* Parser.end).parse(s).map(_._2).
Return a parser that succeeds (consuming nothing and extracting nothing) if the current parser would also succeed.
Return a parser that succeeds (consuming nothing and extracting nothing) if the current parser would also succeed.
This parser expects the underlying parser to succeed, and will unconditionally backtrack after running it.
Wrap this parser in a helper class, to enable backtracking during composition.
Wrap this parser in a helper class, to enable backtracking during composition.
This wrapper changes the behavior of ~, <* and *>. Normally
no backtracking occurs. Using soft on the left-hand side will
enable backtracking if the right-hand side returns an epsilon
failure (but not in any other case).
For example, (x ~ y) will never backtrack. But with (x.soft ~ y), if x parses successfully, and y returns an epsilon
failure, the parser will "rewind" to the point before x began.
Return the string matched by this parser.
Return the string matched by this parser.
When parsing an input string that the underlying parser matches, this parser will return the matched substring instead of any value that the underlying parser would have returned. It will still match exactly the same inputs as the original parser.
This method is very efficient: similarly to void, we can avoid
allocating results to return.
Use this parser to parse surrounded by values.
Use this parser to parse surrounded by values.
This is the same as between(b, b)
Return a parser that succeeds (consuming nothing, and extracting nothing) if the current parser would fail.
Return a parser that succeeds (consuming nothing, and extracting nothing) if the current parser would fail.
This parser expects the underlying parser to fail, and will unconditionally backtrack after running it.
Parse without capturing values.
Parse without capturing values.
Calling void on a parser can be a significant optimization --
it allows the parser to avoid allocating results to return.
Other methods like as, *>, and <* use void internally to
discard allocations, since they will ignore the original parsed
result.
Wrap this parser in a helper class, enabling better composition
with Parser values.
Wrap this parser in a helper class, enabling better composition
with Parser values.
For example, with p: Parser0[Int] and p1: Parser0[Double]:
val a1: Parser0[(Int, Double)] = p ~ p1 val a2: Parser[(Int, Double)] = p.with1 ~ p1
val b1: Parser0[Double] = p *> p1 val b2: Parser[Double] = p.with1 *> p1
val c1: Parser0[Int] = p <* p1 val c2: Parser[Int] = p.with1 <* p1
Without using with1, these methods will return Parser0 values
since they are not known to return Parser values instead.
Add a string context to any Errors on parsing this is useful for debugging failing parsers.
Add a string context to any Errors on parsing this is useful for debugging failing parsers.
Synonym for orElse Note this is not commutative: if this has an arresting failure we do not continue onto the next.
Synonym for orElse Note this is not commutative: if this has an arresting failure we do not continue onto the next.
Sequence another parser after this one, combining both results into a tuple.
Sequence another parser after this one, combining both results into a tuple.
This combinator returns a product of parsers. If this parser
successfully produces an A value, the other parser is run on
the remaining input to try to produce a B value.
If either parser produces an error the result is an error. Otherwise both extracted values are combined into a tuple.