Syntax Differences between ECLiPSe and other Prologs

Properties of ECLiPSe

Some particularities exist in the default syntax of ECLiPSe. Most of these properties can be configured and are in fact changed by the compatibility packages.

• Syntax for the special types of ECLiPSe: metaterms, rationals, bounded reals and array subscript notation.

• by default, a blank space is allowed between the functor and the following opening parenthesis (controlled by syntax option no_blanks)

• end of file is accepted as fullstop

• by default, operators with precedence higher than 1000 are allowed in a comma-separated list of terms, i.e. structure arguments and lists (controlled by syntax option limit_arg_precedence). The ambiguity is resolved by considering commas as argument separators rather than operators inside the term. Thus e.g.

  p(a :- b, c)
  

  is accepted and parsed as p/2.

• double-quoted items are parsed as strings, not as lists (controlled via set_chtab/2)

• empty brackets are not parsed as the atom '[]' when there are layout charactes between the brackets (controlled by syntax option blanks_in_nil)

Changing the Parser behaviour

Some of these properties can be changed by choosing one of the following syntax_options. The following options exist:

blanks_in_nil

allow blanks between the brackets in [].

doubled_quote_is_quote

parse a pair of quotes within a quoted item as one occurrence of the quote within the string. If this option is off (the default), consecutive string-quoted and list-quoted items are parsed as a single (concatenated) item, and consecutive quoted atoms are parsed as consecutive atoms.

limit_arg_precedence

do not allow terms with a precedence higher than 999 as structure arguments, unless parenthesised.

nested_comments

allow bracketed comments to be nested.

nl_in_quotes

allow newlines to occur inside quotes.

no_blanks

do not allow blanks between functor an opening parenthesis

iso_escapes

ISO-Prolog compatible escape sequences within strings and atoms.

iso_base_prefix

allow binary, octal or hexadecimal numbers to be written with 0b, 0o or 0x prefix respectively, and disallow the base'number notation.

$VAR

terms of the form '$VAR'(N) are printed in a special way by all the predicates that obey operator declarations (i.e. write, writeq, print and partly printf). '$VAR'(0) is printed as A, '$VAR'(25) as Z, '$VAR'(26) as A1 and so on. When the argument is an atom or a string, just this argument is printed.

based_bignums

Allow base notation even to write integers longer than the wordsize (i.e. they are always positive).

Syntax option settings can be local to a module or exported, e.g.

:- local syntax_option(not nl_in_quotes).
:- export syntax_option(no_blanks).