One aspect of INTERCAL-72 that was never fully documented was the way
in which IGNORE and RETRIEVE statements interacted. It turns out that
the three modern INTERCAL compilers all use slightly different
definitions.

The associated program ignorret.i stores 1 in a variable's stash, 2 in
the variable itself, ignores the variable, and retrieves it; it then
prints out the variable, and tests to see whether the variable is
ignored.

C-INTERCAL prints:

II

II
In other words, the interpretation used is that the variable is
read-only, so a RETRIEVE can't change its value (but instead just
discards the stash item). The variable remains IGNOREd.

J-INTERCAL prints:

I

I
J-INTERCAL doesn't take the interaction between IGNORE and RETRIEVE
into account at all; the RETRIEVE just does what a RETRIEVE would
normally do, which is to set the variable from its own stack. The
variable remains IGNOREd.

CLC-INTERCAL prints:
I
III
The interpretation used by CLC-INTERCAL is somewhat different. The
ignorance status is stashed along with the variable itself; so the
value of 1 is read from the variable's stash, but doing so also
removes the read-only status of the variable. This means that the
third assignment to the variable works, unlike in the other two
cases. (Note that CLC-INTERCAL will act like C-INTERCAL on the
ignorret test when running in C-INTERCAL compatibility mode.)

The upshot of all this is: don't RETRIEVE a read-only variable if you
want your program to be portable!

Alex Smith