Syntax specification

• TODO out-of-date, fix

The syntax of Dusa is not whitespace-sensitive. Comments, which begin with a pound sign followed by a space or end of line and continue to the end of the line, are treated like whitespace.

Tokens

• A <variable> matches /[A-Z][a-zA-Z0-9_]*/
• A <wildcard> matches /_[a-zA-Z0-9_]*/ and represents variable names that you wish to be ignored.
• An <identifier> matches /[a-z][a-zA-Z0-9_]*/
• A <string-literal> is a regular string constant with no escape characters: two double quotes " surrounding any ASCII character in the range 32-126 except for " and \.
• An <int-literal> matches /0|-?[1-9][0-9]*/

Context-free grammar

<program>      ::= <declaration> <program> | ""
<declaration>  ::= "#builtin" <builtin> <identifier> [ "." ]
                |  "#demand" <premises> "."
                |  "#forbid" <premises> "."
                |  <conclusion> ":-" <premises> "."

<premises>     ::= <premise> | <premise> "," <premises>
<premise>      ::= <term> "!=" <term>
                |  <term> "==" <term>
                |  <attribute>
                |  <attribute> "is" <term>

<conclusion>   ::= <attribute>
                |  <attribute> "is" <term>
                |  <attribute> "is" "{" <options> "}"
<conc-options> ::= <term> | <term> "?" | <conc-option> "," <conc-options>
<conc-option>  ::- <term> | "?"

<attribute>   ::= <identifier> | <identifier> <arguments>
<arguments>   ::= <atomic-term> | <atomic-term> <arguments>
<atomic-term> ::= <wildcard> | <variable>
               |  <string-literal> | <int-literal>
               |  <identifier> | <builtin-identifier>
               |  "(" <term> ")"
<term>        ::= <atomic-term>
               |  <identifier> <arguments>
               |  <builtin-identifier> <arguments>
<builtin>     ::= "INT_PLUS" | "INT_MINUS"
               |  "NAT_ZERO" | "NAT_SUCC"
               |  "STRING_CONCAT"