give things a license

[rust-101.git] / src / part00.rs

diff --git a/src/part00.rs b/src/part00.rs
index 308c242423bfecb1e9adf7b103af85c0b90217ef..1c7d3ce6839ca051053ba77f3494f8233b25041a 100644 (file)
--- a/src/part00.rs
+++ b/src/part00.rs
@@ -1,14 +1,14 @@
-// [index](main.html) | previous | [next](part01.html)
-
-use std;
-

 // Rust-101, Part 00: Algebraic datatypes, expressions
 // ===================================================
 
 // Rust-101, Part 00: Algebraic datatypes, expressions
 // ===================================================
 

-// As a starter, we want to write a function that computes the minimum of a list.
-// First, we need to write down the signature of the function: The types of its arguments and
-// of the return value. In the case of our minimum function,
-// we may be inclined to say that it returns a number. But then we would be in trouble: What's
+// As our first piece of Rust code, we want to write a function that computes the
+// minimum of a list. We are going to make use of the standard library, so let's import that:
+
+use std;
+
+// Let us start by thinking about the *type* of our function. Rust forces us to give the types of
+// all arguments, and the return type, before we even start writing the body. In the case of our minimum
+// function, we may be inclined to say that it returns a number. But then we would be in trouble: What's

 // the minimum of an empty list? The type of the function says we have to return *something*.
 // We could just choose 0, but that would be kind of arbitrary. What we need
 // is a type that is "a number, or nothing". Such a type (of multiple exclusive options)
 // the minimum of an empty list? The type of the function says we have to return *something*.
 // We could just choose 0, but that would be kind of arbitrary. What we need
 // is a type that is "a number, or nothing". Such a type (of multiple exclusive options)


@@ -24,17 +24,17 @@ enum NumberOrNothing {
 // Notice that `i32` is the type of (signed, 32-bit) integers. To write down the type of
 // the minimum function, we need just one more ingredient: `Vec<i32>` is the type of
 // (growable) arrays of numbers, and we will use that as our list type.
 // Notice that `i32` is the type of (signed, 32-bit) integers. To write down the type of
 // the minimum function, we need just one more ingredient: `Vec<i32>` is the type of
 // (growable) arrays of numbers, and we will use that as our list type.

-// Observe how in Rust, the function type comes *after* the arguments.
+// Observe how in Rust, the return type comes *after* the arguments.

 
 fn vec_min_try1(vec: Vec<i32>) -> NumberOrNothing {
     // First, we need some variable to store the minimum as computed so far.
     // Since we start out with nothing computed, this will again be a 
 
 fn vec_min_try1(vec: Vec<i32>) -> NumberOrNothing {
     // First, we need some variable to store the minimum as computed so far.
     // Since we start out with nothing computed, this will again be a 

-    // "number or nothing". Notice that we do not have to write a type
-    // next to `min`, Rust can figure that out automatically (a bit like
-    // `auto` in C++11). Also notice the `mut`: In Rust, variables are
+    // "number or nothing":
+    let mut min = NumberOrNothing::Nothing;
+    // We do not have to write a type next to `min`, Rust can figure that out automatically
+    // (a bit like `auto` in C++11). Also notice the `mut`: In Rust, variables are

     // immutable per default, and you need to tell Rust if you want
     // to change a variable later.
     // immutable per default, and you need to tell Rust if you want
     // to change a variable later.

-    let mut min = NumberOrNothing::Nothing;

 
     // Now we want to *iterate* over the list. Rust has some nice syntax for
     // iterators:
 
     // Now we want to *iterate* over the list. Rust has some nice syntax for
     // iterators:


@@ -43,11 +43,11 @@ fn vec_min_try1(vec: Vec<i32>) -> NumberOrNothing {
         // number in there? This is what pattern matching can do:
         match min {
             NumberOrNothing::Nothing => {
         // number in there? This is what pattern matching can do:
         match min {
             NumberOrNothing::Nothing => {

-                // `min` is currently nothing, so let's just make it the number `el`.
+                // In this case (*arm*) of the `match`, `min` is currently nothing, so let's just make it the number `el`.

                 min = NumberOrNothing::Number(el);
             },
             NumberOrNothing::Number(n) => {
                 min = NumberOrNothing::Number(el);
             },
             NumberOrNothing::Number(n) => {

-                // `min` is currently the number `n`, so let's compute the new minimum and store it.
+                // In this arm, `min` is currently the number `n`, so let's compute the new minimum and store it.

                 let new_min = std::cmp::min(n, el);
                 min = NumberOrNothing::Number(new_min);
             }
                 let new_min = std::cmp::min(n, el);
                 min = NumberOrNothing::Number(new_min);
             }


@@ -64,16 +64,16 @@ use self::NumberOrNothing::{Number,Nothing};
 // Try moving that above the function, and removing all the occurrences `NumberOrNothing::`.
 // Things should still compile, now being much less verbose!
 
 // Try moving that above the function, and removing all the occurrences `NumberOrNothing::`.
 // Things should still compile, now being much less verbose!
 

-// However, the code is still not "idiomatic Rust code". To understand why, it is important to
+// There is more prettification we can do. To understand how, it is important to

 // understand that Rust is an "expression-based" language. This means that most of the
 // terms you write down are not just *statements* (executing code), but *expressions*
 // (returning a value). This applies even to the body of entire functions!
 
 // understand that Rust is an "expression-based" language. This means that most of the
 // terms you write down are not just *statements* (executing code), but *expressions*
 // (returning a value). This applies even to the body of entire functions!
 

-// For example, consider `sqr`. Between the curly braces, we are giving the *expression*
-// that computes the return value. So we can just write `i * i`, the expression that
-// returns the square if `i`, and make that our return value! Note that this is
-// very close to how mathematicians write down functions (but with more types).
+// For example, consider `sqr`:

 fn sqr(i: i32) -> i32 { i * i }
 fn sqr(i: i32) -> i32 { i * i }

+// Between the curly braces, we are giving the *expression* that computes the return value.
+// So we can just write `i * i`, the expression that returns the square if `i`!
+// This is very close to how mathematicians write down functions (but with more types).

 
 // Conditionals are also just expressions. You can compare this to the ternary `? :` operator
 // from languages like C.
 
 // Conditionals are also just expressions. You can compare this to the ternary `? :` operator
 // from languages like C.


@@ -92,8 +92,8 @@ fn number_or_default(n: NumberOrNothing, default: i32) -> i32 {
 fn vec_min(v: Vec<i32>) -> NumberOrNothing {
     let mut min = Nothing;
     for e in v {
 fn vec_min(v: Vec<i32>) -> NumberOrNothing {
     let mut min = Nothing;
     for e in v {

-        // First of all, notice that all we do here is compute a new value for `min`, and that we
-        // will always end up calling the `Number` constructor. In Rust, the structure of the code
+        // First of all, notice that all we do here is compute a new value for `min`, and that it
+        // will always end up being `Number` rather than `Nothing`. In Rust, the structure of the code

         // can express this uniformity as follows:
         min = Number(match min {
             Nothing => e,
         // can express this uniformity as follows:
         min = Number(match min {
             Nothing => e,


@@ -109,19 +109,19 @@ fn vec_min(v: Vec<i32>) -> NumberOrNothing {
 // Now that's already much shorter! Make sure you can go over the code above and actually understand
 // every step of what's going on.
 
 // Now that's already much shorter! Make sure you can go over the code above and actually understand
 // every step of what's going on.
 

-// To call this function, we now just need a list! Of course, ultimately we want to ask the user for
+// To call this function, we now just need a list. Of course, ultimately we want to ask the user for

 // a list of numbers, but for now, let's just hard-code something:
 
 fn read_vec() -> Vec<i32> {
 // a list of numbers, but for now, let's just hard-code something:
 
 fn read_vec() -> Vec<i32> {

+    vec![18,5,7,1,9,27]

     // `vec!` is a *macro* (as you can tell from the `!`) that constructs a constant `Vec` with the given
     // elements.
     // `vec!` is a *macro* (as you can tell from the `!`) that constructs a constant `Vec` with the given
     // elements.

-    vec![18,5,7,1,9,27]

 }
 
 // Finally, let's call our functions and run the code!
 }
 
 // Finally, let's call our functions and run the code!

-// But, wait, we would like to actually see something. Of course Rust can print numbers,
-// but after calling `vec_min`, we have a `NumberOrNothing`. So let's write a small helper
-// function that can prints such values.
+// But, wait, we would like to actually see something, so we need to print the result.
+// Of course Rust can print numbers, but after calling `vec_min`, we have a `NumberOrNothing`.
+// So let's write a small helper function that prints such values.

 
 fn print_number_or_nothing(n: NumberOrNothing) {
     match n {
 
 fn print_number_or_nothing(n: NumberOrNothing) {
     match n {


@@ -130,8 +130,7 @@ fn print_number_or_nothing(n: NumberOrNothing) {
     };
 }
 
     };
 }
 

-// So putting it all together - if you type `cargo run`, it will
-// run the following code:
+// Putting it all together:

 
 pub fn part_main() {
     let vec = read_vec();
 
 pub fn part_main() {
     let vec = read_vec();


@@ -139,6 +138,8 @@ pub fn part_main() {
     print_number_or_nothing(min);
 }
 
     print_number_or_nothing(min);
 }
 

+// Now try `cargo run` on the console to run above code.
+

 // Yay, it said "1"! That's actually the right answer. Okay, we could have
 // computed that ourselves, but that's besides the point. More importantly:
 // You completed the first part of the course.
 // Yay, it said "1"! That's actually the right answer. Okay, we could have
 // computed that ourselves, but that's besides the point. More importantly:
 // You completed the first part of the course.