Narsese

ONA's syntax is mostly compatible with OpenNAR's: https://github.com/opennars/opennars/wiki/Narsese-Grammar-(Input-Output-Format) Most of Narsese is supported, but there are minor differences:

BNF

task ::= sentence

sentence ::= belief | question | goal 

belief ::= statement '. [tense] [truth]

goal ::= statement '! [tense] [desire] 

question ::= statement '? [tense]

statement ::= compound-statement [ copula compound-statement ]

copula ::== '--> | '<-> | '==> | '=/> | '=|>

compound-statement ::=   ['!] compound-term [ statement-operator compound-term ]   // Infix
                       | ['!] statement-operator compound-term compound-term       // Prefix		

statement-operator ::= '&& | '&/ | '&|

compound-term ::=   term [ term-operator term ]     // Infix
                  | term-operator term term	    // Prefix

term-operator ::== '& | '| | '- | '~ | '* | '/1 | '/2 | '\1 | '\2

term ::= ['^] word | set | var | ( statement ) | < statement >

set ::= '{ term [term] '} | '[ term [term] ']

var ::= '$ word | '# word | '? word

word ::= { letter | digit | _ | ” | ' }+

truth ::= '{ float float '}

desire ::= '{ float float '}

tense ::= ':|: //indicating "current time"

Other

Images

(/,rel,_,b) has to be written as

(rel /1 b), and image as

(/,rel,a,_) as

(rel /2 a), same for \ with \1 and \2.

Intervals

Intervals, to measure expected time distances between events, are always learned by ONA and stored as meta-data, they are not part of the Narsese I/O format anymore. Hence a sequence

(&/,a,+5,b)

becomes

(&/,a,b)

or

(a &/ b)

and also the interval for implications is not used anymore.

Operators

The syntactic sugar

(^op,arg_1,...,arg_n)

is not supported anymore, instead the full notation has to be used which is supported by both systems:

<(*,arg_1,...,arg_n) --> ^op>

though for operations without arguments, the following shortcut can be used:

^op

Restrictions

1.

Copulas in ONA are binary, since it's using an array-based heap for terms. While there are ways to encode n-ary relations in a binary heap, the ONA philosophy, following KISS, encourages the use of left-nesting, which is also used by the system itself to compose sequences of events:

((a &/ b) &/ c).

2.

The parallel temporal copula &| is not implemented, please use &/ for now, again due to KISS. If the order does not matter in some background knowledge we want to give the system, in addition to

<(a &/ b) =/> c>

also give it

<(b &/ a) =/> c>

to achieve the same as with &| for now.

Optional syntactic improvements

The ONA parser does not require commas, and doesn't distinguish between < and (, also it supports infix format.

<(|,a,b) --> M>. can be written as

<(a | b) --> M>. or even as

((a | b) --> M).

Note: Spaces cannot be omitted.

Custom truth values

These can be added by appending {0.0 0.9} or alternatively in the old OpenNARS format %0.0;0.9%, for frequency 0.0 and confidence 0.9.