Wisp gotchas

a.asciidoc

Wisp for Node.js

Some stuff that took me longer than it should to grok, figure out, look-up or otherwise non-intuitive or radically different from Clojure.

Functions

namespace

Operates on symbols and keywords but has a implementation which is picky. Takes keywords and symbols as follows: (namespace 'foo/bar), (namespace (keyword "foo" "bar")) or, (namespace (keyword :foo :bar)) all return foo

Macro’s

This would really contain pretty much everything about. It’s just a really tough subject every now and then. But there are these little moments of extremely clarity and insight when you’ve just 'grokked' it thanks to someones super-easy explanation or that 1 golden example code which gave the 'aha' moment.

A few pointers here for and from myself:

1. Quote everything you want executed with a delay, everything you don’t will be evaluated. One way to think of this, is that the quotes get stripped off and when it doesn’t have quotes, they will be evaluated. So a quote acts as a buffer against immediate evaluation/invocation.

(defmacro foo [x]
  (namespace x)) ;=> void(0);

(print (foo wisp/main)) ;=> error

; Add str
(defmacro foo [x]
  (str (namespace x)))

(print (foo wisp/main)) ;=> error

; Ok now properly quote then
(defmacro foo [x]
  (list 'str (namespace x)))

(print (foo wisp/main)) ;=> wisp

So one way to think of this toggling quotes, besides from the perspective of the variable (do I expand or not) we can ask ourselves where does it happen.

One way to get a hint is to do something like:

(defmacro foo []
  (print *ns*))

It will print { id: 'wisp.backend.escodegen.generator', doc: undefined }.

Another thing which will expose something about the nature of macro’s (in wisp) is the following. Consider hacking in some variables, foo, bar and baz.

One could do something as: