Editing Warren Abstract Machine (section)

==Example==
Here is a piece of Prolog code:
<syntaxhighlight lang="prolog">
 girl(sally).
 girl(jane).
 
 boy(B) :- \+ girl(B).
</syntaxhighlight>
A WAM-based Prolog compiler will compile this into WAM instructions similar to the following:
<syntaxhighlight lang="prolog">
 predicate(girl/1):
    switch_on_term(2,1,fail,fail,fail),
 label(1): switch_on_atom([(sally,3),(jane,5)])
 label(2): try_me_else(4)
 label(3): get_atom(sally,0)
           proceed
 label(4): trust_me_else_fail
 label(5): get_atom(jane,0)
           proceed
 
 predicate(boy/1):
    get_variable(x(1),0)
    put_structure(girl/1,0)
    unify_local_value(x(1))
    execute((\+)/1)])
</syntaxhighlight>
An important characteristic of this code is its ability to cope with the various modes in which the predicates can be evoked: any argument might be a variable, a [[ground term]], or a partly instantiated term. The "switch" instructions handle the different cases.