Operator priority evaluation order in Prolog -

if define operator:

op(700, yfx, sum). 

700: rappresent priority respect other operators.

yfx: rappresent precedence of arguments respect operator itself. configuration operator infix , argument y have precedence <= operatore priority , argument x have precedence < of operator priority.

the highest precedence principal functor of therms, means isthe last operation executed..

so, means if have following evalutation:

9 sum 5 sum 7 

so means have 3 in first evvaluate value of 5 sum 7 , evaluate: 9 sum (5 sum 7)

is right reasoning operator priority?

i think wording different you're using:

700: precedence. lower binds more strictly.

yfx: associativity left.

?- write_canonical(1 sum 2 sum 3). yields sum(sum(1,2),3).

this operator associate left, arithmetic binary operators:

?- setof(x-o,current_op(x,yfx,o),l),pairs_keys_values(l,_,os). l = [250- (?), 400- (*), 400- (/), 400- (//), 400- (<<), 400- (>>), 400- (div), 400- (mod), ... - ...|...], os = [?, *, /, //, <<, >>, div, mod, rdiv|...]. 

a practical way inspect operator' relations via unification.

?- (1 sum 2 sum 3) = (1 sum x). false.  ?- (1 sum 2 sum 3) = (x sum 3). x = (1 sum 2). 

note parenthesis required (sum has higher precedence unification (=)/2).

for predefined, systemic, operators see doc page.