Standard Operators

Operators

Logic operators

if

if(A) B else C;
1. A has the form `x=y` and both operands are atomic,
- It uses the reif optimization to avoid creating choice-points.
2. 
- It is expanded to `(A and B) or (not A and C)`.

if(A) B;
- Similar to above. It applies the reif optimization if possible, otherwise expands to `if(A) B else not A;`.

not

1. The statement is an inequality,
- It's reversed, e.g. `not x<=1` expands to _x>1_, `not x=1` expands to _x!=1_.
2. If not,
- A compiler error will be given.

when

when(A) B else C;
- Expands to `(A and B) or C`.

if (function)

Compiles to choose.

not (function)

Negation-as-failure. If A fails, not A succeeds, otherwise fails.

Impure operators

once

If A fails, once A fails. Otherwise, succeed once.

choose

Procedural conditional.

choose(A) B else C;
- If once A succeeds, evaluates B, otherwise evaluate C.

cut

Prolog's cut.