PL/M
Programming Language for Microcomputers
Gary Kildall, MAA (later Digital Research) for Intel, 1972
A very low level language incorporating ideas from PL/I, ALGOL and XPL. It had an integrated macro processor. CP/M was written to support development of the PL/M compiler, not the other way around!.
"PL/M-80 Programming Manual", Doc 98-268B, Intel 1976.
"PL/M Programmer's Guide", Doc 452161-003, Intel.
"A Guide to PL/M Programming for Microcomputer Applications", D. McCracken, Addison-Wesley 1978.
PL/M-80
PL/M-86
PL/M-286
PL/M-386