gistfile1.txt

Composability
In your interfaces, try to use the simplest data structures that work and make
functions do a single, clear thing—if possible, they should be pure functions
(see Chapter 2).
For example, it is not uncommon for modules to provide their own
array-like collection objects, with their own interface for extracting elements
from such an object, and return those from functions that return collections
of things. Such objects cannot be passed to map or forEach. This is a case of
bad composability, since the module cannot be easily composed with algo-
rithms operating on arrays.
Another example would be a module for spellchecking text, which we
might need when we want to write a text editor. The spellchecker could be
made to operate directly on whichever complicated data structures the ed-
itor uses and directly call internal functions in the editor to have the user
choose between spelling suggestions. If we do that, the module cannot be
used with any other programs. On the other hand, if we define the spell-
checking interface so that you can pass it a simple string and it will return
the position in the string where it found a possible misspelling, along with
an array of suggested corrections, then we have an interface that could also
be composed with other systems.