use pushdown in a sentence.
It's a pushdown stack of consolidated tabs.
Which is basically an artificial pushdown of car prices.
I always thought I was playing more like a pushdown automata than a Turing machine.
For finite-state and pushdown automata, derivatives and continuations are two sides of the same coin.
C macros are not Turing complete, they're a pushdown automaton.
You can only imperfectly emulate anything more than a regular language in a finite reality (since a pushdown automaton has an infinite stack).
I've seen the "pushdown" and find it's a great cue for taking a break from the computer.
The grammar itself is context-free and LL(k) and the implementation is trivial once you understand what pushdown automatons are (automata theory, right after finite-state machines).
Perl regular expressions probably accept more than just context-free grammars since the language that accepts prime numbers is not Context-Free, you can't build a pushdown automaton for such a language, there is a relatively trivial proof of this using the pumping lemma for context-free languages.
For those interested in symbolically manipulating  state machines (NFAs), pushdown automata (PDAs), and context-free grammars (CFGs), take a look at .
Interestingly, any physical, finite machine can be modelled as a finite state automaton (which is even more limited than a pushdown automaton) with a large enough state space.
The C preprocessor is a pushdown automaton, which if you add fixpoints (unbounded recursion) becomes a bounded storage machine.
I'm working on an open-source framework, and a series of command line tools built on top of the framework, for symbolically manipulating context-free grammars, non-deterministic pushdown automata, and non-deterministic finite automata.
Although there are some details about what kind of pushdown are supported by the FDWs (for example: to do a WHERE key=x, a non-toy Redis FDW should push the equality predicate to redis), it's no faster nor slower than calling a C function a bunch of times.