1.4 KiB
Partial functions
If a function is supplied with more arguments than it expects, it will throw an exception. If it is supplied with too few arguments, however, it will return a partially-applied function (or partial function for short). This value may then be called with the remaining arguments and the expected result will be returned.
>> add_nums = \x,y,z -> x + y + z
<anon function(3) @58e147c31910>
>> add_nums(5, 6, 8)
19
>> add5 = add_nums(5)
<anon native function(2) @58e147c329e0>
>> add5_and6 = add5(6)
<anon native function(1) @58e147c33360>
>> add5_and6(8)
19
Note that each time the function is given an argument the number the result expects decreases by one.
Pipes
An alternate way of calling a function with one argument is using the pipe
operator (|). The order is reversed to a normal function call - the argument
is written before the pipe.
>> sin(2)
0.9092974268256817
>> 2 | sin
0.9092974268256817
Partial application combines very nicely with pipes: functions may first be called with all but one of their arguments, and the resulting partially-applied function may be called using a pipe.
>> gcd(70, 15)
5
>> 15 | gcd(70)
5
Note that the argument to the left of the pipe becomes the final argument to the function. This is the opposite of langauges like Elixir, in which it becomes the initial argument.
Pipelines will be featured heavily in the chapter on ranges and iterators.