Explain pattern matching in Racket?

Question

I know the gist of pattern matching, where you manipulate data structures upon runtime. I know that pattern matching takes 4 arguments: the pattern to match against, the expression to match, a success continuation, and a failure continuation. However, after that, looking at Racket Documentation I am lost. I don't understand specifically (with concrete, line-by-line, explained examples) how to implement this into a code, and what to do with it. Could someone please explain to me a dumbed-down version of pattern matching, perhaps with a basic code to help me out?

Have you seen the Racket Guide entry on pattern matching? It has some concrete examples. — Asumu Takikawa

Daniel Gratzer Daniel Gratzer · Accepted Answer · 2013-11-27T05:15:01

With pattern matching, we want to tear apart datastructures, so we pass in a piece of data to destruct

(match foo
   ...)

Next we need to specify a list of constructors to try foo against. If foo was constructed by one of those constructors, we bind foos fields to the variables specified and run the associated block.

(match foo
  [(list a b) (+ a b)]
  [_          (displayln "Hey that's not a list!")])

That's it! If foo is a list of two elements, we run + a b if not, we run the other continuation and print that foo isn't a list.

Explain pattern matching in Racket?

2 Answers