Syntax specification

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> [ "." ]
                   |  "#lazy" <identifier> ["."]
                   |  "#demand" <premises> "."
                   |  "#forbid" <premises> "."
                   |  <conclusion> [ ":-" <premises> ] "."

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

<conclusion>      ::= <attribute>
                   |  <attribute> "is" <term-or-choices>
                   |  <attribute> "is?" <term-or-choices>
<term-or-choices> ::= <term> | "{" <choice-options> "}"
<choice-options>  ::= <term> | <term> "," <choice-options>

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