Token Types

TOK_EOF:

The end of file was reached.

TOK_FULLSTOP:

A fullstop (".") followed by white space. This indicates the end of a formula/rule.

TOK_ATOM:

An atom like in Prolog, i.e. a sequence of letters and digits, starting with a lowercase letter. Alternatively a quoted string, e.g. 'abc'.

TOK_CMD:

A command: A dollar sign $, followed by a sequence of letters and digits.

TOK_INT:

An integer, i.e. a sequence of digits, optionally preceded by a minus sign.

TOK_VAR:

A variable like in Prolog, i.e. a sequence of letters and digits starting with an uppercase letter.

TOK_ANONVAR:

The anonymous variable ("_").

TOK_COMMA:

A comma (","). This can be used to separate arguments in an atomic formula and to denote conjunction (as in Prolog).

TOK_LPAREN:

A left paranthesis ("(").

TOK_RPAREN:

A right paranthesis (")").

TOK_MON_OP:

A monadic (prefix) operator, i.e. the "classical negation" sign ("~") or default negation ("not).

TOK_BIN_OP:

A binary operator, i.e. one of the following:

• The conjunction (logical and) operator ("&").
• The disjunction (logical or) operator ("|"). The disjunction can also be written as ";". For compatibility reasons, currently also "v" is still understood.
• The implication (logical if) operator ("<-"). The implication can also be written as in Prolog (":-").
• The implication (logical then) operator ("->").
• Theequivalence operator ("<->").

TOK_QUERY:

A question mark ("?"). It is used to start a query.

TOK_COLON:

A colon (":"). It is used in queries if answer variables are explicitly given.

In addition, there are a number of constants indicating different kinds of lexical errors:

TOK_ILLEGAL_CHAR:

An unknown character - neither alphanumeric nor one of the few special characters which have a defined meaning in SLP.

TOK_LESS:

A less than character ("<") which is not followed by a minus ("-"). Currently the only legal use of the less than character is in the implies operator ("<-").

TOK_MINUS:

A minus character ("-") which is neither followed by a (">") to make it an implication operator, nor by digits. Currently, no arithmetic expressions are supported. So this use of minus is illegal.

TOK_MISSINGQ:

A quoted atom was begun, but there is no closing quote before the line end was reached.

TOK_EMPTYA:

An empty atom ("''") is not allowed.

TOK_NOSPACE:

The fullstop must be followed by white space (as in Prolog). Currently, we treat a "." which is not followed by a space or a newline as an error, and not as an atom.

TOK_INT_OVERFLOW:

This means an integer constant was too large. The minimum and maximum integer are defined in lex.h. Currently, the minum integer is -65536, and the maximum integer is 65535 (i.e. 16-bit integers). So, if the input contains a token like 10000000, its token type would be TOK_INT_OVERFLOW.

TOK_EMPTY_CMD:

Illegal empty command (a dollar sign that is not followed by a letter or number.

TOK_RESERVED_ATOM:

The input was an atom that is internally used, but cannot occur in input programs. At the moment the only such case is "$answer". Normally, the user would get a syntax error message because this is treated as a command on input. This might seem a bit strange, since the user has seen $answer used like an atom in the output. This special token type produces a hopefully clearer message.

tok_name:

str_t tok_name(tok_t tok);
This function returns a string describing the kind of token (e.g. "atom").

• Header File (tok.h)
• Source File (tok.cxx)