The N programming language (1990?) is spookily reminiscent of PyTorch!
> Expecting a wide use of neural network algorithms in the near future, our objective is to get a complete software development environment for programming and testing new applications. We intend to produce a high level language for neural network specification, as a part of such an environment.
> The language we propose is characterized by a high degree of modularity, based on parameterizable data structures, with functionalities in the form of update methods attached to them. Composition rules of structures and methods enable to build, step by step, more complex structures from smaller ones previously defined. Objects are viewed as autonomous modules which are linked through plugs for communications. We particularly cared for the parallelization of methods running concurrently on different objects of the network. The syntax is largely related to those of the C and C++ languages.
M omits the language also known as MUMPS, and also there was a second .Net based language informally called M#, apparently developed by Microsoft Research as part of Midori project, and called "C# for Systems Programming" in public communications from the developers.
I would be shocked if there were any single letters remaining unused for programming languages. We reached <letter>FS saturation for filesystems many years ago, after all.
