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# self_vs_super

This example illustrates the differences between a message to *self* and
a *super* call when calling an inherited meta-predicate. See the comments
in the code for details.

For an in-depth discussion of these concepts, see the corresponding
Handbook glossary entries, the section on "Predicates", and the
reference pages on the the execution-context built-in methods.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

```logtalk
%versions
```

Start by loading the example:

```logtalk
logtalk_load(self_vs_super(loader)).
```

Illustrate the differences between sending a message to _self_ and
making a _super_ call to call an inherited meta-predicate by using
a `foo/1` predicate defined in `user`:

```logtalk
%%table
foo(X).
```

<!--
X = 1 ? ;
X = 2 ? ;
X = 3.
-->

The _super_ calls preserve _sender_ and therefore the `foo/1` predicate
is called by the meta-predicate in the context of `user`:

```logtalk
%%table
proto::meta_super(foo, X).
```

<!--
Execution context for the parent object meta/2 meta-predicate:
  self: proto
  this: parent
  sender: user

X = 1 ? ;
X = 2 ? ;
X = 3.
-->

Messages to _self_ reset _sender_ and therefore the `foo/1` predicate
is called in the context of `proto`, hence the existence error:

```logtalk
catch(proto::meta_self(foo, X), Error, true).
```

<!--
Execution context for the parent object meta/2 meta-predicate:
  self: proto
  this: parent
  sender: proto

Error = error(existence_error(procedure,foo/1),logtalk(call(foo(_307)),c(proto,proto,r(user,proto,c(user,user,r(user,proto,[],[])),[])))).
-->
