Interesting thesis on graphical programming (c. 1966!)

In his thesis entitled The on-line graphical specification of computer procedures, W. R. Sutherland discusses:

An experimental graphical programming system […] created for the TX-2 Computer. With this system, one may draw an arbitrary symbol and give it a meaning. The system has a “macro” capability enabling a new symbol to be defined as a combination of operators. A procedure may be executed after initial values are assigned.

Written in 1966, this was one of the earliest graphical dataflow programming languages, and serves a precursor to Max/MSP and Pure Data.