Is currying just a way to avoid inheritance?

Question

So my understanding of currying (based on SO questions) is that it lets you partially set parameters of a function and return a "truncated" function as a result.

If you have a big hairy function takes 10 parameters and looks like

function (location, type, gender, jumpShot%, SSN, vegetarian, salary) {
    //weird stuff
}

and you want a "subset" function that will let you deal with presets for all but the jumpShot%, shouldn't you just break out a class that inherits from the original function?

I suppose what I'm looking for is a use case for this pattern. Thanks!

Answer 1

Currying has many uses. From simply specifying default parameters for functions you use often to returning specialized functions that serve a specific purpose.

But let me give you this example:

function log_message(log_level, message){}
log_error = curry(log_message, ERROR)
log_warning = curry(log_message, WARNING)

log_message(WARNING, 'This would be a warning')
log_warning('This would also be a warning')

Answer 2

In javascript I do currying on callback functions (because they cannot be passed any parameters after they are called (from the caller)

So something like:

...
var test = "something specifically set in this function";
onSuccess: this.returnCallback.curry(test).bind(this),

// This will fail (because this would pass the var and possibly change it should the function be run elsewhere
onSuccess: this.returnCallback.bind(this,test),
...

// this has 2 params, but in the ajax callback, only the 'ajaxResponse' is passed, so I have to use curry
returnCallback: function(thePassedVar, ajaxResponse){
   // now in here i can have 'thePassedVar', if 
}

I'm not sure if that was detailed or coherent enough... but currying basically lets you 'prefill' the parameters and return a bare function call that already has data filled (instead of requiring you to fill that info at some other point)

Answer 3

When programming in a functional style, you often bind arguments to generate new functions (in this example, predicates) from old. Pseudo-code:

filter(bind_second(greater_than, 5), some_list)

might be equivalent to:

filter({x : x > 5}, some_list)

where {x : x > 5} is an anonymous function definition. That is, it constructs a list of all values from some_list which are greater than 5.