Cheat Sheet

Here are all the tables containing the various Boost.Parser parsers, examples, etc., all in one place. These are repeated elsewhere in different sections of the tutorial.

This table lists all the Boost.Parser parsers. For the callable parsers, a separate entry exists for each possible arity of arguments. For a parser p, if there is no entry for p without arguments, p is a function, and cannot itself be used as a parser; it must be called. In the table below:

each entry is a global object usable directly in your parsers, unless otherwise noted;
"code point" is used to refer to the elements of the input range, which assumes that the parse is being done in the Unicode-aware code path (if the parse is being done in the non-Unicode code path, read "code point" as "char");
RESOLVE() is a notional macro that expands to the resolution of parse argument or evaluation of a parse predicate (see The Parsers And Their Uses);
"RESOLVE(pred) == true" is a shorthand notation for "RESOLVE(pred) is contextually convertible to bool and true"; likewise for false;
c is a character of type char, char8_t, or char32_t;
str is a string literal of type char const[], char8_t const [], or char32_t const [];
pred is a parse predicate;
arg0, arg1, arg2, ... are parse arguments;
a is a semantic action;
r is an object whose type models parsable_range;
p, p1, p2, ... are parsers; and
escapes is a symbols<T> object, where T is char or char32_t.

Note

The definition of parsable_range is:

template<typename T>
concept parsable_range = std::ranges::forward_range<T> &&
    code_unit<std::ranges::range_value_t<T>>;

	Note
	Some of the parsers in this table consume no input. All parsers consume the input they match unless otherwise stated in the table below.

Table 26.1. Parsers and Their Semantics

Parser	Semantics	Attribute Type	Notes
`eps`	Matches epsilon, the empty string. Always matches, and consumes no input.	None.	Matching `eps` an unlimited number of times creates an infinite loop, which is undefined behavior in C++. Boost.Parser will assert in debug mode when it encounters `*eps`, `+eps`, etc (this applies to unconditional `eps` only).
`eps(pred)`	Fails to match the input if `RESOLVE(pred) == false`. Otherwise, the semantics are those of `eps`.	None.
`ws`	Matches a single whitespace code point (see note), according to the Unicode White_Space property.	None.	For more info, see the Unicode properties. `ws` may consume one code point or two. It only consumes two code points when it matches `"\r\n"`.
`eol`	Matches a single newline (see note), following the "hard" line breaks in the Unicode line breaking algorithm.	None.	For more info, see the Unicode Line Breaking Algorithm. `eol` may consume one code point or two. It only consumes two code points when it matches `"\r\n"`.
`eoi`	Matches only at the end of input, and consumes no input.	None.
`attr(arg0)`	Always matches, and consumes no input. Generates the attribute `RESOLVE(arg0)`.	`decltype(RESOLVE(arg0))`.	An important use case for `attribute` is to provide a default attribute value as a trailing alternative. For instance, an optional comma-delmited list is: `int_ % ',' \| attr(std::vector<int>)`. Without the "`\| attr(...)`", at least one `int_` match would be required.
`char_`	Matches any single code point.	The code point type in Unicode parsing, or `char` in non-Unicode parsing. See Attribute Generation.
`char_(arg0)`	Matches exactly the code point `RESOLVE(arg0)`.	The code point type in Unicode parsing, or `char` in non-Unicode parsing. See Attribute Generation.
`char_(arg0, arg1)`	Matches the next code point `n` in the input, if `RESOLVE(arg0) <= n && n <= RESOLVE(arg1)`.	The code point type in Unicode parsing, or `char` in non-Unicode parsing. See Attribute Generation.
`char_(r)`	Matches the next code point `n` in the input, if `n` is one of the code points in `r`.	The code point type in Unicode parsing, or `char` in non-Unicode parsing. See Attribute Generation.	`r` is taken to be in a UTF encoding. The exact UTF used depends on `r`'s element type. If you do not pass UTF encoded ranges for `r`, the behavior of `char_` is undefined. Note that ASCII is a subset of UTF-8, so ASCII is fine. EBCDIC is not. `r` is not copied; a reference to it is taken. The lifetime of `char_(r)` must be within the lifetime of `r`. This overload of `char_` does not take parse arguments.
`cp`	Matches a single code point.	`char32_t`	Similar to `char_`, but with a fixed `char32_t` attribute type; `cp` has all the same call operator overloads as `char_`, though they are not repeated here, for brevity.
`cu`	Matches a single code point.	`char`	Similar to `char_`, but with a fixed `char` attribute type; `cu` has all the same call operator overloads as `char_`, though they are not repeated here, for brevity. Even though the name "`cu`" suggests that this parser match at the code unit level, it does not. The name refers to the attribute type generated, much like the names `int_` versus `uint_`.
`blank`	Equivalent to `ws - eol`.	The code point type in Unicode parsing, or `char` in non-Unicode parsing. See the entry for `char_`.
`control`	Matches a single control-character code point.	The code point type in Unicode parsing, or `char` in non-Unicode parsing. See the entry for `char_`.
`digit`	Matches a single decimal digit code point.	The code point type in Unicode parsing, or `char` in non-Unicode parsing. See the entry for `char_`.
`punct`	Matches a single punctuation code point.	The code point type in Unicode parsing, or `char` in non-Unicode parsing. See the entry for `char_`.
`hex_digit`	Matches a single hexidecimal digit code point.	The code point type in Unicode parsing, or `char` in non-Unicode parsing. See the entry for `char_`.
`lower`	Matches a single lower-case code point.	The code point type in Unicode parsing, or `char` in non-Unicode parsing. See the entry for `char_`.
`upper`	Matches a single upper-case code point.	The code point type in Unicode parsing, or `char` in non-Unicode parsing. See the entry for `char_`.
`lit(c)`	Matches exactly the given code point `c`.	None.	`lit()` does not take parse arguments.
`c_l`	Matches exactly the given code point `c`.	None.	This is a UDL that represents `lit(c)`, for example `'F'_l`.
`lit(r)`	Matches exactly the given string `r`.	None.	`lit()` does not take parse arguments.
`str_l`	Matches exactly the given string `str`.	None.	This is a UDL that represents `lit(s)`, for example `"a string"_l`.
`string(r)`	Matches exactly `r`, and generates the match as an attribute.	`std::string`	`string()` does not take parse arguments.
`str_p`	Matches exactly `str`, and generates the match as an attribute.	`std::string`	This is a UDL that represents `string(s)`, for example `"a string"_p`.
`bool_`	Matches `"true"` or `"false"`.	`bool`
`bin`	Matches a binary unsigned integral value.	`unsigned int`	For example, `bin` would match `"101"`, and generate an attribute of `5u`.
`bin(arg0)`	Matches exactly the binary unsigned integral value `RESOLVE(arg0)`.	`unsigned int`
`oct`	Matches an octal unsigned integral value.	`unsigned int`	For example, `oct` would match `"31"`, and generate an attribute of `25u`.
`oct(arg0)`	Matches exactly the octal unsigned integral value `RESOLVE(arg0)`.	`unsigned int`
`hex`	Matches a hexadecimal unsigned integral value.	`unsigned int`	For example, `hex` would match `"ff"`, and generate an attribute of `255u`.
`hex(arg0)`	Matches exactly the hexadecimal unsigned integral value `RESOLVE(arg0)`.	`unsigned int`
`ushort_`	Matches an unsigned integral value.	`unsigned short`
`ushort_(arg0)`	Matches exactly the unsigned integral value `RESOLVE(arg0)`.	`unsigned short`
`uint_`	Matches an unsigned integral value.	`unsigned int`
`uint_(arg0)`	Matches exactly the unsigned integral value `RESOLVE(arg0)`.	`unsigned int`
`ulong_`	Matches an unsigned integral value.	`unsigned long`
`ulong_(arg0)`	Matches exactly the unsigned integral value `RESOLVE(arg0)`.	`unsigned long`
`ulong_long`	Matches an unsigned integral value.	`unsigned long long`
`ulong_long(arg0)`	Matches exactly the unsigned integral value `RESOLVE(arg0)`.	`unsigned long long`
`short_`	Matches a signed integral value.	`short`
`short_(arg0)`	Matches exactly the signed integral value `RESOLVE(arg0)`.	`short`
`int_`	Matches a signed integral value.	`int`
`int_(arg0)`	Matches exactly the signed integral value `RESOLVE(arg0)`.	`int`
`long_`	Matches a signed integral value.	`long`
`long_(arg0)`	Matches exactly the signed integral value `RESOLVE(arg0)`.	`long`
`long_long`	Matches a signed integral value.	`long long`
`long_long(arg0)`	Matches exactly the signed integral value `RESOLVE(arg0)`.	`long long`
`float_`	Matches a floating-point number. `float_` uses parsing implementation details from Boost.Spirit. The specifics of what formats are accepted can be found in their real number parsers. Note that only the default `RealPolicies` is supported by `float_`.	`float`
`double_`	Matches a floating-point number. `double_` uses parsing implementation details from Boost.Spirit. The specifics of what formats are accepted can be found in their real number parsers. Note that only the default `RealPolicies` is supported by `double_`.	`double`
`repeat(arg0)[p]`	Matches iff `p` matches exactly `RESOLVE(arg0)` times.	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`	The special value `Inf` may be used; it indicates unlimited repetition. `decltype(RESOLVE(arg0))` must be implicitly convertible to `int64_t`. Matching `eps` an unlimited number of times creates an infinite loop, which is undefined behavior in C++. Boost.Parser will assert in debug mode when it encounters `repeat(Inf)[eps]` (this applies to unconditional `eps` only).
`repeat(arg0, arg1)[p]`	Matches iff `p` matches between `RESOLVE(arg0)` and `RESOLVE(arg1)` times, inclusively.	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`	The special value `Inf` may be used for the upper bound; it indicates unlimited repetition. `decltype(RESOLVE(arg0))` and `decltype(RESOLVE(arg1))` each must be implicitly convertible to `int64_t`. Matching `eps` an unlimited number of times creates an infinite loop, which is undefined behavior in C++. Boost.Parser will assert in debug mode when it encounters `repeat(n, Inf)[eps]` (this applies to unconditional `eps` only).
`if_(pred)[p]`	Equivalent to `eps(pred) >> p`.	`std::optional<ATTR(p)>`	It is an error to write `if_(pred)`. That is, it is an error to omit the conditionally matched parser `p`.
`switch_(arg0)(arg1, p1)(arg2, p2) ...`	Equivalent to `p1` when `RESOLVE(arg0) == RESOLVE(arg1)`, `p2` when `RESOLVE(arg0) == RESOLVE(arg2)`, etc. If there is such no `argN`, the behavior of `switch_()` is undefined.	`std::variant<ATTR(p1), ATTR(p2), ...>`	It is an error to write `switch_(arg0)`. That is, it is an error to omit the conditionally matched parsers `p1`, `p2`, ....
`symbols<T>`	`symbols` is an associative container of key, value pairs. Each key is a `std::string` and each value has type `T`. In the Unicode parsing path, the strings are considered to be UTF-8 encoded; in the non-Unicode path, no encoding is assumed. `symbols` Matches the longest prefix `pre` of the input that is equal to one of the keys `k`. If the length `len` of `pre` is zero, and there is no zero-length key, it does not match the input. If `len` is positive, the generated attribute is the value associated with `k`.	`T`	Unlike the other entries in this table, `symbols` is a type, not an object.
`quoted_string`	Matches `'"'`, followed by zero or more characters, followed by `'"'`.	`std::string`	The result does not include the quotes. A quote within the string can be written by escaping it with a backslash. A backslash within the string can be written by writing two consecutive backslashes. Any other use of a backslash will fail the parse. Skipping is disabled while parsing the entire string, as if using `lexeme[]`.
`quoted_string(c)`	Matches `c`, followed by zero or more characters, followed by `c`.	`std::string`	The result does not include the `c` quotes. A `c` within the string can be written by escaping it with a backslash. A backslash within the string can be written by writing two consecutive backslashes. Any other use of a backslash will fail the parse. Skipping is disabled while parsing the entire string, as if using `lexeme[]`.
`quoted_string(r)`	Matches some character `Q` in `r`, followed by zero or more characters, followed by `Q`.	`std::string`	The result does not include the `Q` quotes. A `Q` within the string can be written by escaping it with a backslash. A backslash within the string can be written by writing two consecutive backslashes. Any other use of a backslash will fail the parse. Skipping is disabled while parsing the entire string, as if using `lexeme[]`.
`quoted_string(c, symbols)`	Matches `c`, followed by zero or more characters, followed by `c`.	`std::string`	The result does not include the `c` quotes. A `c` within the string can be written by escaping it with a backslash. A backslash within the string can be written by writing two consecutive backslashes. A backslash followed by a successful match using `symbols` will be interpreted as the corresponding value produced by `symbols`. Any other use of a backslash will fail the parse. Skipping is disabled while parsing the entire string, as if using `lexeme[]`.
`quoted_string(r, symbols)`	Matches some character `Q` in `r`, followed by zero or more characters, followed by `Q`.	`std::string`	The result does not include the `Q` quotes. A `Q` within the string can be written by escaping it with a backslash. A backslash within the string can be written by writing two consecutive backslashes. A backslash followed by a successful match using `symbols` will be interpreted as the corresponding value produced by `symbols`. Any other use of a backslash will fail the parse. Skipping is disabled while parsing the entire string, as if using `lexeme[]`.

Important

All the character parsers, like char_, cp and cu produce either char or char32_t attributes. So when you see "std::string if ATTR(p) is char or char32_t, otherwise std::vector<ATTR(p)>" in the table above, that effectively means that every sequences of character attributes get turned into a std::string. The only time this does not happen is when you introduce your own rules with attributes using another character type (or use attribute to do so).

Operators defined on parsers

Here are all the operator overloaded for parsers. In the tables below:

c is a character of type char or char32_t;
a is a semantic action;
r is an object whose type models parsable_range (see Concepts); and
p, p1, p2, ... are parsers.

	Note
	Some of the expressions in this table consume no input. All parsers consume the input they match unless otherwise stated in the table below.

Table 26.2. Combining Operations and Their Semantics

Expression	Semantics	Attribute Type	Notes
`!p`	Matches iff `p` does not match; consumes no input.	None.
`&p`	Matches iff `p` matches; consumes no input.	None.
`*p`	Parses using `p` repeatedly until `p` no longer matches; always matches.	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`	Matching `eps` an unlimited number of times creates an infinite loop, which is undefined behavior in C++. Boost.Parser will assert in debug mode when it encounters `*eps` (this applies to unconditional `eps` only).
`+p`	Parses using `p` repeatedly until `p` no longer matches; matches iff `p` matches at least once.	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`	Matching `eps` an unlimited number of times creates an infinite loop, which is undefined behavior in C++. Boost.Parser will assert in debug mode when it encounters `+eps` (this applies to unconditional `eps` only).
`-p`	Equivalent to `p \| eps`.	`std::optional<ATTR(p)>`
`p1 >> p2`	Matches iff `p1` matches and then `p2` matches.	`boost::parser::tuple<ATTR(p1), ATTR(p2)>` (See note.)	`>>` is associative; `p1 >> p2 >> p3`, `(p1 >> p2) >> p3`, and `p1 >> (p2 >> p3)` are all equivalent. This attribute type only applies to the case where `p1` and `p2` both generate attributes; see Attribute Generation for the full rules.
`p >> c`	Equivalent to `p >> lit(c)`.	`ATTR(p)`
`p >> r`	Equivalent to `p >> lit(r)`.	`ATTR(p)`
`p1 > p2`	Matches iff `p1` matches and then `p2` matches. No back-tracking is allowed after `p1` matches; if `p1` matches but then `p2` does not, the top-level parse fails.	`boost::parser::tuple<ATTR(p1), ATTR(p2)>` (See note.)	`>` is associative; `p1 > p2 > p3`, `(p1 > p2) > p3`, and `p1 > (p2 > p3)` are all equivalent. This attribute type only applies to the case where `p1` and `p2` both generate attributes; see Attribute Generation for the full rules.
`p > c`	Equivalent to `p > lit(c)`.	`ATTR(p)`
`p > r`	Equivalent to `p > lit(r)`.	`ATTR(p)`
`p1 \| p2`	Matches iff either `p1` matches or `p2` matches.	`std::variant<ATTR(p1), ATTR(p2)>` (See note.)	`\|` is associative; `p1 \| p2 \| p3`, `(p1 \| p2) \| p3`, and `p1 \| (p2 \| p3)` are all equivalent. This attribute type only applies to the case where `p1` and `p2` both generate attributes, and where the attribute types are different; see Attribute Generation for the full rules.
`p \| c`	Equivalent to `p \| lit(c)`.	`ATTR(p)`
`p \| r`	Equivalent to `p \| lit(r)`.	`ATTR(p)`
`p1 \|\| p2`	Matches iff `p1` matches and `p2` matches, regardless of the order they match in.	`boost::parser::tuple<ATTR(p1), ATTR(p2)>`	`\|\|` is associative; `p1 \|\| p2 \|\| p3`, `(p1 \|\| p2) \|\| p3`, and `p1 \|\| (p2 \|\| p3)` are all equivalent. It is an error to include a `eps` (conditional or non-conditional) in an `operator\|\|` expression. Though the parsers are matched in any order, the attribute elements are always in the order written in the `operator\|\|` expression.
`p1 - p2`	Equivalent to `!p2 >> p1`.	`ATTR(p1)`
`p - c`	Equivalent to `p - lit(c)`.	`ATTR(p)`
`p - r`	Equivalent to `p - lit(r)`.	`ATTR(p)`
`p1 % p2`	Equivalent to `p1 >> *(p2 >> p1)`.	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p1)>`
`p % c`	Equivalent to `p % lit(c)`.	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`
`p % r`	Equivalent to `p % lit(r)`.	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`
`p[a]`	Matches iff `p` matches. If `p` matches, the semantic action `a` is executed.	None.

Important

There are a couple of special rules not captured in the table above:

First, the zero-or-more and one-or-more repetitions (operator*() and operator+(), respectively) may collapse when combined. For any parser p, +(+p) collapses to +p; **p, *+p, and +*p each collapse to just *p.

Second, using eps in an alternative parser as any alternative except the last one is a common source of errors; Boost.Parser disallows it. This is true because, for any parser p, eps | p is equivalent to eps, since eps always matches. This is not true for eps parameterized with a condition. For any condition cond, eps(cond) is allowed to appear anywhere within an alternative parser.

Attribute generation for certain parsers

This table summarizes the attributes generated for all Boost.Parser parsers. In the table below:

RESOLVE() is a notional macro that expands to the resolution of parse argument or evaluation of a parse predicate (see The Parsers And Their Uses); and
x and y represent arbitrary objects.

Table 26.3. Parsers and Their Attributes

Parser	Attribute Type	Notes
`eps`	None.
`eol`	None.
`eoi`	None.
`attr(x)`	`decltype(RESOLVE(x))`
`char_`	The code point type in Unicode parsing, or `char` in non-Unicode parsing; see below.	Includes all the `_p` UDLs that take a single character, and all character class parsers like `control` and `lower`.
`cp`	`char32_t`
`cu`	`char`
`lit(x)`	None.	Includes all the `_l` UDLs.
`string(x)`	`std::string`	Includes all the `_p` UDLs that take a string.
`bool_`	`bool`
`bin`	`unsigned int`
`oct`	`unsigned int`
`hex`	`unsigned int`
`ushort_`	`unsigned short`
`uint_`	`unsigned int`
`ulong_`	`unsigned long`
`ulong_long`	`unsigned long long`
`short_`	`short`
`int_`	`int`
`long_`	`long`
`long_long`	`long long`
`float_`	`float`
`double_`	`double`
`symbols<T>`	`T`

char_ is a bit odd, since its attribute type is polymorphic. When you use char_ to parse text in the non-Unicode code path (i.e. a string of char), the attribute is char. When you use the exact same char_ to parse in the Unicode-aware code path, all matching is code point based, and so the attribute type is the type used to represent code points, char32_t. All parsing of UTF-8 falls under this case.

Here, we're parsing plain chars, meaning that the parsing is in the non-Unicode code path, the attribute of char_ is char:

auto result = parse("some text", boost::parser::char_);
static_assert(std::is_same_v<decltype(result), std::optional<char>>));

When you parse UTF-8, the matching is done on a code point basis, so the attribute type is char32_t:

auto result = parse("some text" | boost::parser::as_utf8, boost::parser::char_);
static_assert(std::is_same_v<decltype(result), std::optional<char32_t>>));

The good news is that usually you don't parse characters individually. When you parse with char_, you usually parse repetition of then, which will produce a std::string, regardless of whether you're in Unicode parsing mode or not. If you do need to parse individual characters, and want to lock down their attribute type, you can use cp and/or cu to enforce a non-polymorphic attribute type.

Attributes for operations on parsers

Combining operations of course affect the generation of attributes. In the tables below:

m and n are parse arguments that resolve to integral values;
pred is a parse predicate;
arg0, arg1, arg2, ... are parse arguments;
a is a semantic action; and
p, p1, p2, ... are parsers that generate attributes.

Table 26.4. Combining Operations and Their Attributes

Parser	Attribute Type
`!p`	None.
`&p`	None.
`*p`	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`
`+p`	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`
`+*p`	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`
`*+p`	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`
`-p`	`std::optional<ATTR(p)>`
`p1 >> p2`	`boost::parser::tuple<ATTR(p1), ATTR(p2)>`
`p1 > p2`	`boost::parser::tuple<ATTR(p1), ATTR(p2)>`
`p1 >> p2 >> p3`	`boost::parser::tuple<ATTR(p1), ATTR(p2), ATTR(p3)>`
`p1 > p2 >> p3`	`boost::parser::tuple<ATTR(p1), ATTR(p2), ATTR(p3)>`
`p1 >> p2 > p3`	`boost::parser::tuple<ATTR(p1), ATTR(p2), ATTR(p3)>`
`p1 > p2 > p3`	`boost::parser::tuple<ATTR(p1), ATTR(p2), ATTR(p3)>`
`p1 \| p2`	`std::variant<ATTR(p1), ATTR(p2)>`
`p1 \| p2 \| p3`	`std::variant<ATTR(p1), ATTR(p2), ATTR(p3)>`
`p1 \|\| p2`	`boost::parser::tuple<ATTR(p1), ATTR(p2)>`
`p1 \|\| p2 \|\| p3`	`boost::parser::tuple<ATTR(p1), ATTR(p2), ATTR(p3)>`
`p1 % p2`	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p1)>`
`p[a]`	None.
`repeat(arg0)[p]`	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`
`repeat(arg0, arg1)[p]`	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`
`if_(pred)[p]`	`std::optional<ATTR(p)>`
`switch_(arg0)(arg1, p1)(arg2, p2)...`	`std::variant<ATTR(p1), ATTR(p2), ...>`

Important

	Important
	In case you did not notice it above, adding a semantic action to a parser erases the parser's attribute. The attribute is still available inside the semantic action as `_attr(ctx)`.

More attributes for operations on parsers

In the table: a is a semantic action; and p, p1, p2, ... are parsers that generate attributes. Note that only >> is used here; > has the exact same attribute generation rules.

Table 26.5. Sequence and Alternative Combining Operations and Their Attributes

Expression	Attribute Type
`eps >> eps`	None.
`p >> eps`	`ATTR(p)`
`eps >> p`	`ATTR(p)`
`cu >> string("str")`	`std::string`
`string("str") >> cu`	`std::string`
`*cu >> string("str")`	`boost::parser::tuple<std::string, std::string>`
`string("str") >> *cu`	`boost::parser::tuple<std::string, std::string>`
`p >> p`	`boost::parser::tuple<ATTR(p), ATTR(p)>`
`*p >> p`	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`
`p >> *p`	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`
`*p >> -p`	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`
`-p >> *p`	`std::string` if `ATTR(p)` is `char` or `char32_t`, otherwise `std::vector<ATTR(p)>`
`string("str") >> -cu`	`std::string`
`-cu >> string("str")`	`std::string`
`!p1 \| p2[a]`	None.
`p \| p`	`ATTR(p)`
`p1 \| p2`	`std::variant<ATTR(p1), ATTR(p2)>`
`p \|eps`	`std::optional<ATTR(p)>`
`p1 \| p2 \| eps`	`std::optional<std::variant<ATTR(p1), ATTR(p2)>>`
`p1 \| p2[a] \| p3`	`std::optional<std::variant<ATTR(p1), ATTR(p3)>>`

Boost C++ Libraries

Cheat Sheet

The parsers

Operators defined on parsers

Attribute generation for certain parsers

Attributes for operations on parsers

More attributes for operations on parsers