docs: added some basic language constructs to the docs

* refactor: integrated highlight.js with mun support
* docs: added some basic language constructs to the docs

Co-Authored-By: Wodann <[email protected]>

src/SUMMARY.md

@@ -3,7 +3,7 @@
 [Introduction](ch00-00-introduction.md)
 [Case studies](ch00-01-case-studio-abbey-games.md)
 
-## Types
-
-- [Types](ch01-00-types.md)
+- [Basic concepts](ch01-00-basic-concepts.md)
+    - [Values and types](ch01-01-values-and-types.md)
+    - [Control flow](ch01-02-control-flow.md)
 

src/ch01-00-basic-concepts.md

@@ -0,0 +1,5 @@
+# Basic Concepts
+
+This section describes the basic concepts of the Mun programming language.
+
+

src/ch01-01-values-and-types.md

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+# Values and types
+
+Mun is a statically typed language, which helps to detect type-related errors at
+compile-time. A type error is an invalid operation on a given type, such as an
+integer divided by a string, trying to access a field that doesn't exist, or
+calling a function with the wrong number of arguments.
+
+Some languages require a programmer to explicitly annotate syntactic constructs
+with type information:
+
+```c++
+int foo = 3 + 4;
+```
+
+However, often variable types can be inferred by their usage. Mun uses type
+inferencing to determine variable types at compile time. However, you are still
+forced to explicitly annotate variables in a few locations to ensure a contract
+between interdependent code.
+
+```mun
+fn bar(a:int):int {
+    let foo = 3 + a
+    foo
+}
+```
+
+Here, the parameter `a` and the return type must be annotated because it solidifies
+the signature of the function. The type of `foo` can be inferred through its
+usage.
+
+## Basic types
+
+Mun knows two basic numeric types: `float` and `int`. A `float` is a
+double-precision IEEE 64-bit floating point number and an `int` represents a
+64-bit integral number.
+
+In Mun an `int` can be explicitly cast to `float`, but the reverse is not true.
+Assigning a `float` to an `int` might cause loss of precision and can therefore
+not be cast implicitly.
+
+A `bool` has two possible values: `true` and `false`.
+
+## Implicit & explicit returns
+
+A block is a grouping of statements and expressions surrounded by curly braces.
+Function bodies are an example of blocks. In Mun, blocks evaluate to the last
+expression in them. Blocks can therefore also be used on the right hand side of a
+`let` statement.
+
+```mun
+fn foo():int {
+    let bar = {
+        let b = 3;
+        b+3
+    }
+
+    // `bar` has a value 6
+    bar+3
+}
+```
+
+Besides implicit returns, explicit returns can also be used with `return`
+expressions. However, explicit `return` statements always return from the
+function, not from the block:
+
+```mun
+fn foo():int {
+    let bar = {
+        let b = 3;
+        return b+3
+    }
+
+    // This code will never be executed
+    return bar+3;
+}
+```
+
+## Shadowing
+
+> WIP

src/ch01-02-control-flow.md

@@ -0,0 +1,66 @@
+# Control flow
+
+Executing or repeating a block of code only under specific conditions are common
+constructs that allow developers to control the flow of execution. Mun provides
+ `if...else` expressions and loops.
+
+## `if` expressions
+
+An `if` expression allows you to branch your code depending on conditions.
+
+```mun
+fn main() {
+    let number = 3;
+
+    if number < 5 {
+        number = 4;
+    } else {
+        number = 6;
+    }
+}
+```
+
+All `if` expressions start with the keyword `if`, followed by a condition.
+As opposed to many C-like languages, Mun omits parentheses around the
+condition. Only when the condition is true - in the example, whether the `number`
+variable is less than 5 - the consecutive code block (or *arm*) is executed.
+
+Optionally, an `else` expression can be added that will be executed when the
+condition evaluates to false. You can also have multiple conditions by combining
+`if` and `else` in an `else if` expression. For example:
+
+```mun
+fn main() {
+    let number = 6;
+    if number > 10 {
+        // The number if larger than 10
+    } else if number > 8 {
+        // The number is larger than 8 but smaller or equal to 10
+    } else if number > 2 {
+        // The number is larger than 2 but smaller or equal to 8
+    } else {
+        // The number is smaller than- or equal to 2.
+    }
+}
+```
+
+
+### Using `if` in a `let` statement
+
+The `if` expression can be used on the right side of a `let` statement
+just like a block:
+
+```mun
+fn main() {
+    let condition = true;
+    let number = if condition {
+        5
+    } else {
+        6
+    };
+```
+
+Depending on the condition, the `number` variable will be bound to the value
+of the `if` block or the `else` block. This means that both the `if` and `else`
+arms need to evaluate to the same type.
+If the types are mismatched the compiler will report an error.