matchbook
v1.0.2
Published
Declarative function overloading
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Matchbook
Like switch
on runtime steroids, for easily creating overloaded functions.
# CoffeeScript
pattern = 'matchbook'
myFunc = pattern (match) ->
# TODO: interesting example
// ES 6
let pattern = require('matchbook');
let myFunc = pattern(match => {
// TODO: interesting example
});
// ES 5
var pattern = require('matchbook');
var myFunc = pattern(function(match) {
// TODO: interesting example
});
Patterns
Valid patterns are:
- "classes" (constructor functions)
- The built-in functions
Number
,String
,Boolean
,Function
, andArray
are special-cased.
- The built-in functions
- arbitrary predicates:
If(x => x > 0)
- arrays of patterns:
[String, Number, Int]
- objects of patterns:
{ foo: String, bar: Function }
- literal values:
1
,null
,true
,void 0
, etc.
Note that the special-cased primitive patterns (like Number
and String
) only match primitive values (like 123
and foo
), not boxed values (like new Number(123)
and new String('foo')
).
API
Matchbook exports a function, which I'll call pattern
.
let pattern = require('matchbook');
Attached to pattern
are some other functions:
pattern.compile(pattern)
- converts a pattern into a predicate -- a function that tests that pattern on the given value
- this is not necessary if you're using the
pattern
function directly, but can be useful in other cases
pattern.Any
- a pattern that matches any value, including
undefined
- a pattern that matches any value, including
pattern.If(predicate)
- returns a predicate-based function
pattern.List(pattern)
- returns a pattern that matches on iterators (such as
Array
s, and generators) only if each element matches the supplied pattern
- returns a pattern that matches on iterators (such as
pattern.Or(pattern1, pattern2)
- returns a pattern that succeeds if either supplied pattern matches
pattern.And(pattern1, pattern2)
- returns a pattern that matches if both supplied patterns match
- example:
And(Number, If(x => x > 0))
pattern.overload
- a synonym for
pattern
, for more convenient destructuring imports.
- a synonym for
Extracting values from patterns
This is not supported, and cannot be implemented in vanilla JavaScript without some horrible abuse of eval
. If it's an option for you, consider a SweetJS-based pattern matcher like Sparkler instead.
Default values, spreads, and views
There is no support yet for default values of functions, nor for spreads, nor for views. But these would not be hard to add, and I'd be happy to do so if there's interest. Or I'll just go ahead and do it if I encounter a need myself.
Compatibility
Matchbook will not work in IE 8 or below.