Tue 2022-11-22

Extending the standard context

Lately I've been using this function in cases where I want to redefine the standard context std:

\extend==
    (\cx\form
    \cx=cx
    value;
    (@\std\form cx; def "std" std; form);
    form
    )

Example:

\flintstones=(value; std; use "flintstones.fxl")

extend
(\form
std;
flintstones;
form
) \;

# At this point "std" has been redefined to include the flintstones context,
# exactly as if its definitions were built in.

fred
wilma

However, there may be cases where I want to use another module but I don't want that module to see the new definitions. In that case I could keep a handle to the original std context, by giving it a name such as cx_base.

\flintstones=(value; std; use "flintstones.fxl")

extend
(\form
std;
flintstones;
def "cx_base" std;
form
) \;

# Now I can choose which module can see the new flintstones definitions:

\A=(value; cx_base; use "A.fxl")  # Cannot see flintstones
\B=(value; std; use "B.fxl")      # Can see flintstones

That can be particularly useful if the new definitions include some potentially dangerous functions and I don't always want them available.

I will soon include extend in the standard library.