Screwtape Letter #32: Is Go a Functional Programming Language?
Tuesday, February 8, 2011 at 10:01PM My Beloved Wormwood,
I was delighted to find that you're learning about concurrent programming. It was excellent news that your headmaster decided to allow multi-core CPUs in His Eminence's data center. We are certainly the benefactors of less expensive computers, and the work to limit tithing paid to churches shows promise. You'll find answers to you questions below.
Sincerely,
Uncle Screwtape
Is Go a functional programming language?
No. Absolutely not. This assertion is completely ridiculous.
Does Go offer functions?
Of course Go has functions. Most programming language offer functions. Oh, you don’t believe me? I’ll show you.
fmt.Println("Hello")
}
There. I just wrote a simple function in Go. Just type the key word “func” and specify a name for it. I called my function “SayHello” because that’s what it does. After the function name you have to specify its input parameters inside parenthesis. My function doesn’t require any input parameters so I just typed an empty set of parenthesis. Finally, you must add the logic of the function inside a set of brackets.
Can Go functions accept arguments?
Well, I see this idiotic line of questioning continues. Oh I understand, programming is not immediately intuitive, so I’ll explain.
fmt.Println("Hello " + name + ".")
}
Yes, functions in Go can accept arguments. As you can see, I changed our SayHello function to be a bit more personal. It now accepts a name, presumably a patient, then responds by saying hello to that patient via the console.
Can Go functions return a value?
Yes, yes, yes! Just like in math. Remember Slipslop’s lectures on faith and function? A function such as f(x) = x + 2 would add 2 to the value of x. Let’s build upon our first function. I’ll make a new function called GetGreeting that will return a string.
greeting := "Hello " + name + "."
return greeting
}
greeting := GetGreeting("Bob")
fmt.Println(greeting) //outputs "Hello Bob."
You can also declare the name of the variable to be returned by the function in the function declaration itself. This gives you a couple of things for free. First, you won’t have to re-declare the variable in the function body. Second, you don’t have to specify the variable name after the return statement. The function will implicitly return the said variable in its last known state.
greeting = "Hello " + name + "."
return
}
greeting := GetGreeting("Bob")
fmt.Println(greeting) //outputs "Hello Bob."
Can Go functions accept a function?
Well, I see you’re starting to pay attention. We might just make a programmer out of you yet. Wouldn’t it be nice to say hello to a list of patients you’d like to torment?
Let’s make a struct called TormentList that is composed of a slice of patients. A slice is similar to an array.
patients []string
}
func NewTormentList(people []string) *TormentList {
return &TormentList{people}
}
Now lets quietly, without disturbing any functional programmers, attach a method to TormentList which will apply a function to each item in the slice.
for _, val := range(g.patients) {
f(val)
}
}
Map’s single argument is a function f, which accepts a string, and returns nothing. This function iterates over TormentList’s patients, applying the function to each blessed soul in the process. Why don’t we try this out?
gl := NewTormentList(patients)
gl.Map(SayHelloToSomeone)
/*
outputs the following:
Hello Anand.
Hello David.
Hello Ivan.
Hello JoJo.
Hello Jin.
Hello Mon.
Hello Peter.
Hello Sachin.
*/
Can Go functions return a function?
My beloved Wormwood, you’re walking a fine line between an imperative programming and a functional programming. I’ll dismiss this reckless abandon once. But you must swear to keep this example to yourself. Under no circumstance should Joe Armstrong, our mortal enemy and creator of Erlang, discover this.
Let’s discuss a real world scenario. As you know we like to help The Department of Homeland Security impede the plans of American travelers. Just the other day, I saw a security guard discover day old sushimi in a tourist’s pocket. He confiscated the tuna fish and ate it immediately. That’s when I thought of using Go to screen travellers who had recently eaten sushi. This will help security guards fish out spoiled tuna to eat, which will surely lead to indigestion problems and subsequent longer processing times.
return func(name string) bool {
for _, soul := range patients {
if soul == name {
return true
}
}
return false
}
}
Now that we have a function, we can make a list of all patients who used their credit card to purchase sushi within the last 24 hours.
Now we can pass our list of patients to the Screen function and, in turn, receive a “Bought Sushi?” detector.
fmt.Println(bought_sushi("Anand")) // true
fmt.Println(bought_sushi("Alex")) // false
Go enables us to do work in one paradigm, while under the guise of another. Like us, it's wonderfully deceptive.
Reader Comments (17)
When you said:
func (g *TormentList) Map(f(func(string))) {
I think you meant
func (g *TormentList) Map(f func(string)) {
Franz,
Thank you for the code fix!
Charles
Extremely useful writeup, left me asking for more!!..
Cool post on the useful codes. I am not good at these so I totally appreciate the information learned from you. Thanks.
Adeel Chowdhry
SalesLetters Creator
Does Go offer Tail Recursion?
Whoops, no.
Adeel, are you sure that gccgo doesn't provide tail recursion? Is there a reason why Go doesn't have tail recursion other than it simply hasn't been implemented yet?
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By the way Go interfaces do not participate in a type hierarchy like Java's. They are better described as a set of methods, identified by their name and signature.
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