PublicShow -- Define Quasi Quotation syntax

Inspired by Haskell, SWI-Prolog support quasi quotation. Quasi quotation allows for embedding (long) strings using the syntax of an external language (e.g., HTML, SQL) in Prolog text and syntax-aware embedding of Prolog variables in this syntax. At the same time, quasi quotation provides an alternative to represent long strings and atoms in Prolog.

The basic form of a quasi quotation is defined below. Here, Syntax is an arbitrary Prolog term that must parse into a callable (atom or compound) term and Quotation is an arbitrary sequence of characters, not including the sequence |}. If this sequence needs to be embedded, it must be escaped according to the rules of the target language or the `quoter' must provide an escaping mechanism.


While reading a Prolog term, and if the Prolog flag quasi_quotes is set to true (which is the case if this library is loaded), the parser collects quasi quotations. After reading the final full stop, the parser makes the call below. Here, SyntaxName is the functor name of Syntax above and SyntaxArgs is a list holding the arguments, i.e., Syntax =.. [SyntaxName|SyntaxArgs]. Splitting the syntax into its name and arguments is done to make the quasi quotation parser a predicate with a consistent arity 4, regardless of the number of additional arguments.

call(+SyntaxName, +Content, +SyntaxArgs, +VariableNames, -Result)

The arguments are defined as

The file library(http/html_quasiquotations) provides the, suprisingly simple, quasi quotation parser for HTML.

- Jan Wielemaker. Introduction of Quasi Quotation was suggested by Michael Hendricks.
See also
- Why it's nice to be quoted: quasiquoting for haskell
Sourcewith_quasi_quotation_input(+Content, -Stream, :Goal) is det
Process the quasi-quoted Content using Stream parsed by Goal. Stream is a temporary stream with the following properties:
  • Its initial position represents the position of the start of the quoted material.
  • It is a text stream, using utf8 encoding.
  • It allows for repositioning
  • It will be closed after Goal completes.
Goal- is executed as once(Goal). Goal must succeed. Failure or exceptions from Goal are interpreted as syntax errors.
See also
- phrase_from_quasi_quotation/2 can be used to process a quotation using a grammar.
Sourcephrase_from_quasi_quotation(:Grammar, +Content) is det
Process the quasi quotation using the DCG Grammar. Failure of the grammer is interpreted as a syntax error.
See also
- with_quasi_quotation_input/3 for processing quotations from stream.
Sourcequasi_quotation_syntax(:SyntaxName) is det
Declare the predicate SyntaxName/4 to implement the the quasi quote syntax SyntaxName. Normally used as a directive.
Report syntax_error(Error) using the current location in the quasi quoted input parser.
- error(syntax_error(Error), Position)