Did you know ... | Search Documentation: |

This library provides various commonly used DCG primitives acting on
list of character **codes**. Character classification is based on
code_type/2.

This module started its life as library(http/dcg_basics) to support the HTTP protocol. Since then, it was increasingly used in code that has no relation to HTTP and therefore this library was moved to the core library.

**string_without**`(+EndCodes, -Codes)`// is**det**- Take as many codes from the input until the next character code
appears in the list
`EndCodes`. The terminating code itself is left on the input. Typical use is to read upto a defined delimiter such as a newline or other reserved character. For example:..., string_without("\n", RestOfLine)

**string**`(-Codes)`// is**nondet**- Take as few as possible tokens from the input, taking one more
each time on backtracking. This code is normally followed by a
test for a delimiter. For example:
upto_colon(Atom) --> string(Codes), ":", !, { atom_codes(Atom, Codes) }.

**blanks**// is**det**- Skip zero or more white-space characters.
**blank**// is**semidet**- Take next
`space`

character from input. Space characters include newline. **nonblanks**`(-Codes)`// is**det**- Take all
`graph`

characters **nonblank**`(-Code)`// is**semidet**`Code`is the next non-blank (`graph`

) character.**blanks_to_nl**// is**semidet**- Take a sequence of blank//0 codes if blanks are followed by a newline or end of the input.
**whites**// is**det**- Skip white space
*inside*a line. **white**// is**semidet**- Take next
`white`

character from input. White characters do*not*include newline. **alpha_to_lower**`(?C)`// is**semidet**- Read a letter (class
`alpha`

) and return it as a lowercase letter. If`C`is instantiated and the DCG list is already bound,`C`must be`lower`

and matches both a lower and uppercase letter. If the output list is unbound, its first element is bound to`C`. For example:?- alpha_to_lower(0'a, `AB`, R). R = [66]. ?- alpha_to_lower(C, `AB`, R). C = 97, R = [66]. ?- alpha_to_lower(0'a, L, R). L = [97|R].

**digits**`(?Chars)`// is**det****digit**`(?Char)`// is**det****integer**`(?Integer)`// is**det**- Number processing. The predicate digits//1 matches a posibly empty set of digits, digit//1 processes a single digit and integer processes an optional sign followed by a non-empty sequence of digits into an integer.
**float**`(?Float)`// is**det**- Process a floating point number. The actual conversion is controlled by number_codes/2.
**number**`(+Number)`// is**det****number**`(-Number)`// is**semidet**- Generate extract a number. Handles both integers and floating point numbers.
**xinteger**`(+Integer)`// is**det****xinteger**`(-Integer)`// is**semidet**- Generate or extract an integer from a sequence of hexadecimal digits.
**xdigit**`(-Weight)`// is**semidet**- True if the next code is a hexdecimal digit with
`Weight`.`Weight`is between 0 and 15. **xdigits**`(-WeightList)`// is**det**- List of weights of a sequence of hexadecimal codes.
`WeightList`may be empty. **eos**//- Matches end-of-input. The implementation behaves as the
following portable implementation:
eos --> call(eos_). eos_([], []).

**remainder**`(-List)`//- Unify
`List`with the remainder of the input. **prolog_var_name**`(-Name:atom)`// is**semidet**- Matches a Prolog variable name. Primarily intended to deal with quasi quotations that embed Prolog variables.
**atom**`(++Atom)`// is**det**- Generate codes of
`Atom`. Current implementation uses write/1, dealing with any Prolog term.`Atom`must be ground though. **digits**`(?Chars)`// is**det****digit**`(?Char)`// is**det****integer**`(?Integer)`// is**det**- Number processing. The predicate digits//1 matches a posibly empty set of digits, digit//1 processes a single digit and integer processes an optional sign followed by a non-empty sequence of digits into an integer.
**digits**`(?Chars)`// is**det****digit**`(?Char)`// is**det****integer**`(?Integer)`// is**det**- Number processing. The predicate digits//1 matches a posibly empty set of digits, digit//1 processes a single digit and integer processes an optional sign followed by a non-empty sequence of digits into an integer.