There's a common cliché, that C programs, as embodied in Unix, are probably the most widely used form of functional programming - or at least CSP. This example is idiomatic;

     grep -c foo * | uniq | sort -rn

It's more than possible to structure C programs this way internally too, elegant even. Use forks and pipes if you want to keep it simple, build co-routines if you're up for it. It's probably the most practical and beneficial way you can re-apply the lessons of FP to C.

But the book doesn't mention either technique - just weird and ugly tricks to emulate tail-recursion, cons et al, probably the least effective parts of FP to try to use in C.