format code in md

solutions/functional-programing/closure.md

@@ -1,4 +1,5 @@
 1、
+
 ```rust
 fn main() {
     let color = String::from("green");
@@ -13,6 +14,7 @@ fn main() {
 ```
 
 2、
+
 ```rust
 fn main() {
     let mut count = 0;
@@ -38,6 +40,7 @@ fn main() {
 ```
 
 3、
+
 ```rust
 fn main() {
      // A non-copy type.
@@ -83,6 +86,7 @@ fn take<T>(_v: &T) {
 ```
 
 4、
+
 ```rust
 fn main() {
     let example_closure = |x| x;
@@ -95,6 +99,7 @@ fn main() {
 ```
 
 5、
+
 ```rust
 fn fn_once<F>(func: F)
 where
@@ -126,6 +131,7 @@ fn main() {
 ```
 
 6、
+
 ```rust
 fn main() {
     let mut s = String::new();
@@ -143,6 +149,7 @@ fn exec<'a, F: FnMut(&'a str)>(mut f: F)  {
 ```
 
 7、
+
 ```rust
 // A function which takes a closure as an argument and calls it.
 // <F> denotes that F is a "Generic type parameter"
@@ -197,6 +204,7 @@ fn main() {
 ```
 
 8、
+
 ```rust
 fn main() {
     let mut s = String::new();
@@ -212,6 +220,7 @@ fn exec<'a, F: FnOnce(&'a str) -> String>(mut f: F) {
 ```
 
 9、
+
 ```rust
 // Define a function which takes a generic `F` argument
 // bounded by `Fn`, and calls it
@@ -234,6 +243,7 @@ fn main() {
 ```
 
 10、
+
 ```rust
 /* Fill in the blank and fix the errror */
 // You can aslo use `impl FnOnce(i32) -> i32`
@@ -268,6 +278,7 @@ fn main() {
 ```
 
 11、
+
 ```rust
 // Every closure has its own type. Even if one closure has the same representation as another, their types are different.
 fn factory(x:i32) -> Box<dyn Fn(i32) -> i32> {