[wrycoder]

Or another Knuth book, The Stanford Graph Base?

Early C compilers, prior to prototypes, were rigid about the order of the various functions and includes, and that interfered with the exposition of the design. Literate programming was created by Knuth to address that.

[housel]

TeX (and Metafont, and the original Tangle and Weave) were written in Pascal, which is much more rigid with respect to ordering than early C was. The CWEB used for the Stanford Graphbase came later. (Silvio Levy did the initial adaptation of Pascal WEB to C, and Knuth took it over when he switched to programming in C.)