SICStus Prolog

Note carefully the following syntax restrictions, which serve to remove potential ambiguity associated with prefix operators.

In a term written in standard syntax, the principal functor and its following ( must not be separated by any intervening layout-text. Thus
```
point (X,Y,Z)
```
is invalid syntax.
If the argument of a prefix operator starts with a (, this ( must be separated from the operator by at least one layout-char. Thus
```
:-(p;q),r.
```
(where :- is the prefix operator) is invalid syntax. The system would try to interpret it as the compound term:
```
    ,
   / \
 :-    r
  |
  ;
 / \
p   q
```
That is, it would take :- to be a functor of arity 1. However, since the arguments of a compound term are required to be expressions of precedence below 1000, this interpretation would fail as soon as the ; (precedence 1100) was encountered.
In contrast, the term:
```
:- (p;q),r.
```
is valid syntax and represents the following compound term:
```
   :-
    |
    ,
   / \
  ;   r
 / \
p   q
```