By the fact that lmm said "You can pass functions", they probably meant "function pointers", since that's the only way you can pass in something that could be referred to as a function in C.

EDIT: At least last I heard. The example I gave is C89, and I know C99 and some GNU extensions. I don't know if a new standard introduced something else that could be referred to as a function that can be passed in but not returned.

A quick google for "c lambda" and "c closure" as well as looking for those keywords in the Wikipedia articles of C11 and C18 turned up nothing, so I guess not.

GNU c can have lambda expressions[1]. And clang does even have closures[2].

1: http://walfield.org/blog/2010/08/25/lambdas-in-c.html

2: https://en.wikipedia.org/wiki/Blocks_(C_language_extension)

Note that the first example relies on multiple GCC-only features, one of which is the atrocity that is nested functions, and even then technically invokes undefined behavior.

GNU C has "downward funarg" closures, like Pascal. They have the same representation as function pointers, which requires the compiled code to generate trampolines (little pieces of machine code that find a PC-relative environment pointer) on the stack. Invoking them requires executable stacks (a linker-level executable option often now turned off by default in major GNU/Linux distros).