Partial application
The second transformation we will be considering lets you fix some of the function’s parameters, creating a new function that will receive the rest of them. Let’s make this clear with a nonsense example. Imagine you have a function with five parameters. You might want to fix the second and fifth parameters, and partial application would produce a new version of the function that fixed those two parameters but left the other three open for new calls. If you called the resulting function with the three required arguments, it would produce the correct answer by using the original two fixed parameters plus the newly provided three.
Projecting parameters
The idea of specifying only some parameters in function application, producing a function of the remaining parameters, is called projection: you are said to be projecting the function onto the remaining arguments. We will not use this term, but I wanted to cite it in case you find it elsewhere.
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