CHARACTER PARSERS

any_char

Parses any character, returning a pair of the character at the current State's position and the new state, advanced by one from the starting state. If the state is at the end ("$state-"eof> is true), returns undef to signal failure.

char $c

Parses the given character $c, returning a pair of the character at the current State's position if it is equal to $c and the new state, advanced by one from the starting state. If the state is at the end ("$state-"eof> is true) or the character at the current position is not $c, returns undef to signal failure.

string $s

Parses the given string $s, returning a pair of the sequence of characters starting at the current State's position if it is equal to $s and the new state, advanced by "length($s)" from the starting state. If the state is at the end ("$state-"eof> is true) or the string starting at the current position is not $s, returns undef to signal failure.

NUMBER PARSERS

endianness [$end]

When the $end argument is given, this functions sets the byte order used by parsers in the module to be little- (when $end is "<") or big-endian ($end is ">"). This function changes the module's state and remains in effect until the next change.

When called with no arguments, "endianness" returns the current byte order in effect. The starting byte order is big-endian.

any_uint8, any_uint16, any_uint24, any_uint32

Parses an 8-, 16-, 24-, and 32-bit unsigned integer, returning a pair of the integer starting at the current State's position and the new state, advanced by 1, 2, 3, or 4 bytes from the starting state, depending on the parser. The integer value is determined by the current value of "endianness". If there are not enough elements left in the data from the current position, returns undef to signal failure.

uint8 $n, uint16 $n, uint24 $n, uint32 $n

Parses the specified 8-, 16-, 24-, and 32-bit unsigned integer $n, returning a pair of the integer at the current State's position if it is equal $n and the new state. The new state is advanced by 1, 2, 3, or 4 bytes from the starting state, depending on the parser. The integer value is determined by the current value of "endianness". If there are not enough elements left in the data from the current position or the current position is not $n, returns undef to signal failure.

any_int8, any_int16, any_int24, any_int32

Parses an 8-, 16-, 24-, and 32-bit signed integer, returning a pair of the integer starting at the current State's position and the new state, advanced by 1, 2, 3, or 4 bytes from the starting state, depending on the parser. The integer value is determined by the current value of "endianness". If there are not enough elements left in the data from the current position, returns undef to signal failure.

int8 $n, int16 $n, int24 $n, int32 $n

Parses the specified 8-, 16-, 24-, and 32-bit signed integer $n, returning a pair of the integer at the current State's position if it is equal $n and the new state. The new state is advanced by 1, 2, 3, or 4 bytes from the starting state, depending on the parser. The integer value is determined by the current value of "endianness". If there are not enough elements left in the data from the current position or the current position is not $n, returns undef to signal failure.

any_real32, any_real64

Parses an 32- or 64-bit real number, returning a pair of the number starting at the current State's position and the new state, advanced by 4 or 8 bytes from the starting state, depending on the parser. The real value is determined by the current value of "endianness". If there are not enough elements left in the data from the current position, returns undef to signal failure.

any_int32_na, any_real64_na

Parses a 32-bit signed integer or 64-bit real number, respectively, but recognizing R-style missing values (NAs): INT_MIN for integers and a special NaN bit pattern for reals. Returns a pair of the number value ("undef" if a NA) and the new state, advanced by 4 or 8 bytes from the starting state, depending on the parser. If there are not enough elements left in the data from the current position, returns undef to signal failure.

SEQUENCING

seq $p1, ...

This combinator applies parsers $p1, ... in sequence, using the returned parse state of $p1 as the input parse state to $p2, etc. Returns a pair of the concatenation of all the parsers' results and the parsing state returned by the final parser. If any of the parsers returns undef, "seq" will return it immediately without attempting to apply any further parsers.

many_till $p, $end

This combinator applies a parser $p until parser $end succeeds. It does this by alternating applications of $end and $p; once $end succeeds, the function returns the concatenation of results of preceding applications of $p. (Thus, if $end succeeds immediately, the 'result' is an empty list.) Otherwise, $p is applied and must succeed, and the procedure repeats. Returns a pair of the concatenation of all the $p's results and the parsing state returned by the final parser. If any applications of $p returns undef, "many_till" will return it immediately.

count $n, $p

This combinator applies the parser $p exactly $n times in sequence, threading the parse state through each call. Returns a pair of the concatenation of all the parsers' results and the parsing state returned by the final application. If any application of $p returns undef, "count" will return it immediately without attempting any more applications.

with_count [$num_p = any_uint32], $p

This combinator first applies parser $num_p to get the number of times that $p should be applied in sequence. If only one argument is given, "any_uint32" is used as the default value of $num_p. (So "with_count" works by getting a number $n by applying $num_p and then calling "count $n, $p".) Returns a pair of the concatenation of all the parsers' results and the parsing state returned by the final application. If the initial application of $num_p or any application of $p returns undef, "with_count" will return it immediately without attempting any more applications.

choose $p1, ...

This combinator applies parsers $p1, ... in sequence, until one of them succeeds, when it immediately returns the parser's result. If all of the parsers fail, "choose" fails and returns undef

COMBINATORS

bind $p1, $f

This combinator applies parser $p1 and, if it succeeds, calls function $f using the first element of $p1's result as the argument. The call to $f needs to return a parser, which "bind" applies to the parsing state after $p1's application.

The "bind" combinator is an essential building block for most combinators described so far. For instance, "with_count" can be written as:

    bind($num_p,
         sub {
             my $n = shift;
             count $n, $p;
         })
    

mreturn $value

Returns a parser that when applied returns $value without changing the parsing state.

error $message

Returns a parser that when applied croaks with the $message and the current parsing state.

SINGLETONS

These functions are an interface to ParseState's singleton-related functions, "add_singleton" in ParseState and "get_singleton" in ParseState. They exist because certain types of objects in R data files, for instance environments, have to exist as unique instances, and any subsequent objects that include them refer to them by a "reference id".

add_singleton $singleton

Adds the $singleton to the current parsing state. Returns a pair of $singleton and the new parsing state.

get_singleton $ref_id

Retrieves from the current parse state the singleton identified by $ref_id, returning a pair of the singleton and the (unchanged) state.

reserve_singleton $p

Preallocates a space for a singleton before running a given parser, and then assigns the parser's value to the singleton. Returns a pair of the singleton and the new parse state.