Class-less Coding – Minimalist C# and Why F# and Function Programming Has Some Advantages

Summary

Can we use just the native .NET classes for developing code, rather than immediately writing an application specific class that often is little more than a container?  Can we do this using aliases, a fluent style, and extension methods?  If we’re going to just use .NET classes, we’re going to end up using generic dictionaries, tuples, and lists, which gets unwieldy very quickly.  We can alias these types with using statements, but this means copying these using statements into every .cs file where we want to use the alias.  A fluent (“dot-style”) notation reduces code lines by representing code in a “workflow-style” notation.  In C#, if we don’t write classes with member methods, then we have to implement behaviors as extensions methods.  Using aliases improves semantic readability at one level at the cost of confusing generic type nesting in the alias definition.  Extension methods can be taken too far, resulting in two  rules: write lower level functions for semantic expressiveness, and avoid nested parens that require the programmer to maintain a mental “stack” of the workflow.  In contrast to C#’s using aliases, F# type definitions are not aliases, they are concrete types.  New type definitions can be created from existing types.  Type definitions can also be used to specify a function’s parameters and return value.  The forward pipe operator |> is similar to the fluent “dot” notation in C#, but the value on the left of the |> operator “populates” the last parameter in the function’s parameter list.  When functions are written that return something, the last function must be piped to the ignore function, which is slightly awkward.  F# type dependencies are based on the order of the files in the project, so a type must be defined before you use it.  In C#, creating more complex aliases get messy real fast — this is an experiment, not a recommendation for coding practices!  In F#, we don’t need an Action or Func class for passing functions because F# inherently supports type definitions that declare a function’s parameters and return value — in other words, everything in functional programming is actually a function.  Tuples are a class in C# but native to functional programming, though C# 6.0 makes using tuples very similar to F#.  While C# allows function parameters to be null, in F#, you have to pass in an actual function, even if the function does nothing.  F# uses a nominal (“by name”) as opposed to structural inference engine, Giving types semantically meaningful names is very important so that the type inference engine can infer the correct type.  In C#, changing the members of class doesn’t affect the class type.  Not so with F# (at least with vanilla records) — changing the structure of a record changes the record’s type.  Changing the members of a C# class can, among other things, lead to incorrect initialization and usage.   Inheritance, particularly in conjunction with mutable fields, can result in behaviors with implicit understanding like “this will never happen” to suddenly break.  Extension methods and overloading creates semantic ambiguity.  Overloading is actually not supported in F# – functions must have semantically different names, not just different types or parameters lists.  Object oriented programming and functional programming both have their pros and cons, with some hopefully concrete discussion presented here.

Full article on Code Project here.

Partial Application and Currying in C# – Clearing the Fog

Partial Application vs. Currying

Most of the examples you’ll see on the regarding partial application and currying (even in F#) often talk about simple functions that take two parameters.  This is sort of pointless because when you partially apply one parameter or curry one parameter, the call to resolve the operation is identical, so you really don’t get an appreciation of the syntactical difference.  I, however, will avoid that by demonstrating the differences between partial application and currying using three (wow!) parameters.

Partial Application

Very simply, partial application lets you assign the first n parameters, returning a function that takes the rest.  Given a function that returns the sum of three values:

Func<int, int, int, int> add = (a, b, c) => a + b + c;

You can partially apply one or two parameters:

Func<int, int, int> needsTwoMoreParams = (b, c) => add(3, b, c);
Func<int, int> needsOneMoreParam = (c) => add(3, 4, c);

Using these functions looks like this:

int twelve = needsTwoMoreParams(4, 5); 
twelve = needsOneMoreParam(5);

Notice we have to explicitly define the return type of the partial application function.  We cannot use var!

var needsOneParam = (b, c) => add(3, b, c);

Cannot assign lambda expression to an implicit-typed variable.

In a functional programming language like F#, the type is inferred:

> let add a b c = a + b + c;;
val add : a:int -> b:int -> c:int -> int

> let add3 = add 3;;
val add3 : (int -> int -> int)

> let add3and4 = add 3 4;;
val add3and4 : (int -> int)

The key thing to note with partial application in C# is the construct (b, c) for the remaining parameters in the needsTwoMoreParams function.  This is what tells you it’s a partial application rather than currying!

You can do the same thing with functions that are not C# Func types but Action types:

Action<int, int, int> xadd = (a, b, c) => Console.WriteLine(a + b + c);
Action<int, int> xoneParam = (b, c) => add(3, b, c);
Action<int> xtwoParams = (c) => add(3, 4, c);

Currying

As Jon Skeet so eloquently wrote: “currying effectively decomposes the function into functions taking a single parameter.”  Study this example carefully:

Func<int, Func<int, Func<int, int>>> curried = a => b => c => a + b + c;
int twelve = curried(3)(4)(5);
Func<int, Func<int, int>> oneParam = curried(3);
Func<int, int> twoParams = curried(3)(4);
twelve = twoParams(5);

Note how the parameters of the curried function are called as separate parameters: (3)(4)(5).  Also note that the function is defined with a => b
=> c=>, which tells you this is a curried function!

Interestingly, we can use var in this case:

var oneParam = curried(3);
var twoParams = curried(3)(4);

Again however, the syntax in C# for defining the curried function must be explicit – “a function that takes an int that returns a function that takes an int and returns a function that takes an int and returns an int.”  This gets ugly real quick, and again, in F#, the inference engine knows you’re doing currying:

> add(3);;
val it : (int -> int -> int) = <fun:it@9>

> let add3 = add(3);;
val add3 : (int -> int -> int)

> let add3and4 = add(3)(4);;
val add3and4 : (int -> int)

> add3and4(5);;
val it : int = 12

Also notice this in F#:

add3(4, 5);;
add3(4, 5);;
-----^^^^

stdin(13,6): error FS0001: This expression was expected to have type
'int' 
but here has type
''a * 'b'

The correct syntax, in F# looks just like C# – one parameter per “function”:

> add3(4)(5);;
val it : int = 12

Again, once you create a curried function, you have to treat it like a curried function, same as in C#.

What about curried functions of an Action?  It would look like this:

Func<int, Func<int, Action<int>>> curried = a => b => c => Console.WriteLine(a + b + c);

var oneParam = curried(3);
var twoParams = curried(3)(4);
twoParams(5);  // prints 12

Note how the final result of last Func is an Action that takes the last value.

So now hopefully you have a clear understanding of the difference between partial application and currying.