Transformation Operations

proplists:append_values/2

A curious function that wraps each value in a list unless it’s already a list, then concatenates everything:

lfe> (proplists:append_values 'include 
      '((include (one two)) (other 42) (include three) (include (four))))
(one two three four)

This is often useful for “incremental” options where you want to accumulate values across multiple sources. It’s the functional programming equivalent of pushing items onto a stack, except the stack is inside-out and upside-down.

proplists:compact/1

Minimizes the representation by converting everything to normal form:

lfe> (proplists:compact '((a true) (b false) (c 42) d (e true)))
(a (b false) (c 42) d e)

This is equivalent to mapping property/1 over the list, which means {Key, true} becomes just Key while everything else stays as it is. The result is aesthetically pleasing in the way that a freshly organized desk is aesthetically pleasing—you’re not entirely sure what changed, but it looks better.

proplists:unfold/1

The inverse of compact/1, expanding all atoms to explicit tuples:

lfe> (proplists:unfold '(read write (mode binary)))
((read true) (write true) (mode binary))

This makes the implicit explicit, which is sometimes necessary when interfacing with systems that lack the sophistication to understand shorthand.