Programming Arduino in Pascal?
Not Pascal, but Ada, which is much less restrictive than Pascal while enjoying the same advantages over low-level programming, and much more actively supported with language revisions as recently as 2012 and the formally provable SPARK language, for when you need your code to work.

Any processor which gcc supports can potentially support Ada, whose Gnat compiler is fully part of gcc.

That's not the whole story because you also need run-time system support for Ada's facilities, but for the Arduino's AVR processor there is a well established environment in the form of the AVR-Ada project.

It generates nice tight little executables, you'll be amazed how much less space simple Gnat executables take compared to Arduino ones - unless you've already made the same comparison between Arduino and C ... which after all uses the same gcc compiler.

For ARM-based Arduinos (Arduino Due at least) the same is possible, though the support is newer and possibly less well established, see the Cortex-GNAT project.

Leaving the Arduino, Ada has also been demonstrated on the MSP430 processor - my own project, sadly neglected at the moment.