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