Implement vec based scopes

- Replaced vartable hashmap with vec
- Use linear search in reverse to find the variables by name
- This is really fast with a small number of variables but tanks fast
  with more vars due to O(n) lookup times
- Implemented scopes by dropping all elements from the vartable at the
  end of a scope

Cargo.toml

@@ -4,3 +4,5 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
+anyhow = "1.0.53"
+thiserror = "1.0.30"

README.md

@@ -1,7 +1,212 @@
 # NEK-Lang
 
+## Variables
+Currently all variables are global and completely unscoped. That means no matter where a variable is declared, it remains over the whole remaining runtime of the progam.
+
+All variables are currently of type `i64` (64-bit signed integer)
+
+### Declaration
+- Declare and initialize a new variable
+- Declaring a previously declared variable again is currently equivalent to an assignment
+- Declaration is needed before assignment or other usage
+- The variable name is on the left side of the `<-` operator
+- The assigned value is on the right side and can be any expression
+```
+a <- 123;
+```
+Create a new variable named `a` and assign the value `123` to it.
+
+### Assignment
+- Assigning a value to a previously declared variable
+- The variable name is on the left side of the `=` operator
+- The assigned value is on the right side and can be any expression
+```
+a = 123;
+```
+The value `123` is assigned to the variable named `a`. `a` needs to be declared before this.
+
+## Expressions
+The operator precedence is the same order as in `C` for all implemented operators. 
+Refer to the 
+[C Operator Precedence Table](https://en.cppreference.com/w/c/language/operator_precedence) 
+to see the different precedences.
+
+### General
+- Parentheses `(` and `)` can be used to modify evaluation oder just like in any other 
+programming language.
+- For example `(a + b) * c` will evaluate the addition before the multiplication, despite the multiplication having higher binding power
+
+### Mathematical Operators
+Supported mathematical operations:
+- Addition `a + b`
+- Subtraction `a - b`
+- Multiplication `a * b`
+- Division `a / b`
+- Modulo `a % b`
+- Negation `-a`
+
+### Bitwise Operators
+- And `a & b`
+- Or `a | b`
+- Xor `a ^ b`
+- Bitshift left (by `b` bits) `a << b`
+- Bitshift right (by `b` bits) `a >> b`
+- "Bit flip" (One's complement) `~a`
+
+### Logical Operators
+The logical operators evaluate the operands as `false` if they are equal to `0` and `true` if they are not equal to `0`
+- And `a && b`
+- Or `a || b`
+- Not `!a` (if `a` is equal to `0`, the result is `1`, otherwise the result is `0`)
+
+### Equality & Relational Operators
+The equality and relational operations result in `1` if the condition is evaluated as `true` and in `0` if the condition is evaluated as `false`.
+- Equality `a == b`
+- Inequality `a != b`
+- Greater than `a > b`
+- Greater or equal than `a >= b`
+- Less than `a < b`
+- Less or equal than `a <= b`
+
+## Control-Flow
+For conditions like in if or loops, every non zero value is equal to `true`, and `0` is `false`.
+
+### Loop
+- There is currently only the `loop` keyword that can act like a `while` with optional advancement (an expression that is executed after the loop body)
+- The `loop` keyword is followed by the condition (an expression) without needing parentheses
+- *Optional:* If there is a `;` after the condition, there must be another expression which is used as the advancement
+- The loops body is wrapped in braces (`{ }`) just like in C/C++
+
+```
+// Print the numbers from 0 to 9
+
+// Without advancement
+i <- 0;
+loop i < 10 {
+  print i;
+  i = i - 1;
+}
+
+// With advancement
+k <- 0;
+loop k < 10; k = k - 1 {
+  print k;
+}
+```
+
+### If / Else
+
+- The language supports `if` and an optional `else`
+- After the `if` keyword must be the deciding condition, parentheses are not needed
+- The block *if-true* block is wrapped in braces (`{ }`)
+- *Optional:* If there is an `else` after the *if-block*, there must be a following *if-false*, aka. else block
+```
+a <- 1;
+b <- 2;
+if a == b {
+  // a is equal to b
+  print 1;
+} else {
+  // a is not equal to b
+  print 0;
+}
+```
+
+## IO
+
+### Print
+Printing is implemented via the `print` keyword
+- The `print` keyword is followed by an expression, the value of which will be printed to the terminal.
+- Print currently automatically adds a linebreak
+```
+a <- 1;
+print a; // Outputs `"1\n"` to the terminal
+```
+
+## Comments
+
+### Line comments
+Line comments can be initiated by using `//`
+- Everything after `//` up to the end of the current line is ignored and not parsed
+```
+// This is a comment
+```
+
+
+# Feature Tracker
+
 ## High level Components
 
-- [ ] Lexer: Transforms text into Tokens
+- [x] Lexer: Transforms text into Tokens
-- [ ] Parser: Transforms Tokens into Abstract Syntax Tree
+- [x] Parser: Transforms Tokens into Abstract Syntax Tree
-- [ ] Interpreter (tree-walk-interpreter): Walks the tree and evaluates the expressions / statements
+- [x] Interpreter (tree-walk-interpreter): Walks the tree and evaluates the expressions / statements
+
+## Language features
+
+- [x] General expressions
+  - [x] Arithmetic operations
+    - [x] Addition `a + b`
+    - [x] Subtraction `a - b`
+    - [x] Multiplication `a * b`
+    - [x] Division `a / b`
+    - [x] Modulo `a % b
+    - [x] Negate `-a`
+  - [x] Parentheses `(a + b) * c`
+  - [x] Logical boolean operators
+    - [x] Equal `a == b`
+    - [x] Not equal `a != b`
+    - [x] Greater than `a > b`
+    - [x] Less than `a < b`
+    - [x] Greater than or equal `a >= b`
+    - [x] Less than or equal `a <= b`
+  - [x] Logical operators
+    - [x] And `a && b`
+    - [x] Or `a || b`
+    - [x] Not `!a`
+  - [x] Bitwise operators
+    - [x] Bitwise AND `a & b`
+    - [x] Bitwise OR `a | b`
+    - [x] Bitwise XOR `a ^ b`
+    - [x] Bitwise NOT `~a`
+    - [x] Bitwise left shift `a << b`
+    - [x] Bitwise right shift `a >> b`
+- [x] Variables
+  - [x] Declaration
+  - [x] Assignment
+- [x] Statements with semicolon & Multiline programs
+- [x] Control flow
+  - [x] While loop `while X { ... }`
+  - [x] If else statement `if X { ... } else { ... }`
+    - [x] If Statement
+    - [x] Else statement
+- [x] Line comments `//`
+- [x] Strings
+- [x] IO Intrinsics
+  - [x] Print
+
+## Grammar
+
+### Expressions
+```
+LITERAL = I64_LITERAL | STR_LITERAL
+expr_primary = LITERAL | IDENT | "(" expr ")" | "-" expr_primary | "~" expr_primary
+expr_mul = expr_primary (("*" | "/" | "%") expr_primary)*
+expr_add = expr_mul (("+" | "-") expr_mul)*
+expr_shift = expr_add ((">>" | "<<") expr_add)*
+expr_rel = expr_shift ((">" | ">=" | "<" | "<=") expr_shift)*
+expr_equ = expr_rel (("==" | "!=") expr_rel)*
+expr_band = expr_equ ("&" expr_equ)*
+expr_bxor = expr_band ("^" expr_band)*
+expr_bor = expr_bxor ("|" expr_bxor)*
+expr_land = expr_bor ("&&" expr_bor)*
+expr_lor = expr_land ("||" expr_land)*
+expr = expr_lor
+```
+
+### Statements
+```
+stmt_if = "if" expr "{" stmt* "}" ("else" "{" stmt* "}")?
+stmt_loop = "loop" expr (";" expr)? "{" stmt* "}"
+stmt_expr = expr ";"
+stmt = stmt_expr | stmt_loop
+```

examples/euler1.nek

@@ -0,0 +1,15 @@
+// If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. 
+// The sum of these multiples is 23.
+// Find the sum of all the multiples of 3 or 5 below 1000.
+// 
+// Correct Answer: 233168
+
+sum <- 0;
+i <- 0;
+loop i < 1_000; i = i + 1 {
+    if i % 3 == 0 | i % 5 == 0 {
+        sum = sum + i;
+    }
+}
+
+print sum;

examples/euler2.nek

@@ -0,0 +1,26 @@
+// Each new term in the Fibonacci sequence is generated by adding the previous two terms. 
+// By starting with 1 and 2, the first 10 terms will be:
+//   1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
+// By considering the terms in the Fibonacci sequence whose values do not exceed four million, 
+// find the sum of the even-valued terms.
+// 
+// Correct Answer: 4613732
+
+sum <- 0;
+
+a <- 0;
+b <- 1;
+tmp <- 0;
+
+loop a < 4_000_000 {
+    if a % 2 == 0 {
+        sum = sum + a;
+    }
+
+    tmp = a;
+    a = b;
+    b = b + tmp;
+}
+
+print sum;
+

examples/euler3.nek

@@ -0,0 +1,29 @@
+// The prime factors of 13195 are 5, 7, 13 and 29.
+// What is the largest prime factor of the number 600851475143 ?
+// 
+// Correct Answer: 6857
+
+number <- 600_851_475_143;
+result <- 0;
+
+div <- 2;
+
+loop number > 1 {
+    loop number % div == 0 {
+        if div > result {
+            result = div;
+        }
+        number = number / div;
+    }
+
+    div = div + 1;
+    if div * div > number {
+        if number > 1 & number > result {
+            result = number;
+        }
+        number = 0;
+    }
+
+}
+
+print result;

examples/euler4.nek

@@ -0,0 +1,36 @@
+// A palindromic number reads the same both ways. The largest palindrome made from the product of 
+// two 2-digit numbers is 9009 = 91 × 99.
+// Find the largest palindrome made from the product of two 3-digit numbers.
+// 
+// Correct Answer: 906609
+
+
+res <- 0;
+
+tmp <- 0;
+num <- 0;
+num_rev <- 0;
+
+i <- 100;
+k <- 100;
+loop i < 1_000; i = i + 1 {
+    k = 100;
+    loop k < 1_000; k = k + 1 {
+        num_rev = 0;
+
+        num = i * k;
+
+        tmp = num;
+
+        loop tmp {
+            num_rev = num_rev*10 + tmp % 10;
+            tmp = tmp / 10;
+        }
+
+        if num == num_rev & num > res {
+            res = num;
+        }
+    }
+}
+
+print res;

examples/euler4.py

@@ -0,0 +1,24 @@
+# A palindromic number reads the same both ways. The largest palindrome made from the product of 
+# two 2-digit numbers is 9009 = 91 × 99.
+# Find the largest palindrome made from the product of two 3-digit numbers.
+# 
+# Correct Answer: 906609
+
+
+res = 0
+
+for i in range(100, 999):
+    for k in range(100, 999):
+
+        num = i * k
+        tmp = num
+
+        num_rev = 0
+        while tmp != 0:
+            num_rev = num_rev*10 + tmp % 10
+            tmp = tmp // 10
+        
+        if num == num_rev and num > res:
+            res = num
+
+print(res)

examples/euler5.nek

@@ -0,0 +1,28 @@
+// 2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder.
+// What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20?
+// 
+// Correct Answer: 232_792_560
+
+num <- 20;
+should_continue <- 1;
+i <- 2;
+
+loop should_continue {
+    should_continue = 0;
+
+    i = 20;
+    loop i >= 2; i = i - 1 {
+        if num % i != 0 {
+            should_continue = 1;
+            
+            // break
+            i = 0;
+        }
+    }
+
+    if should_continue == 1 {
+        num = num + 20;
+    }
+}
+
+print num;

src/ast.rs

@@ -0,0 +1,150 @@
+use std::rc::Rc;
+
+/// Types for binary operators
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub enum BinOpType {
+    /// Addition
+    Add,
+
+    /// Subtraction
+    Sub,
+
+    /// Multiplication
+    Mul,
+
+    /// Divide
+    Div,
+
+    /// Modulo
+    Mod,
+
+    /// Compare Equal
+    EquEqu,
+
+    /// Compare Not Equal
+    NotEqu,
+
+    /// Less than
+    Less,
+
+    /// Less than or Equal
+    LessEqu,
+
+    /// Greater than
+    Greater,
+
+    /// Greater than or Equal
+    GreaterEqu,
+
+    /// Bitwise OR (inclusive or)
+    BOr,
+
+    /// Bitwise And
+    BAnd,
+
+    /// Bitwise Xor (exclusive or)
+    BXor,
+
+    /// Logical And
+    LAnd,
+
+    /// Logical Or
+    LOr,
+
+    /// Shift Left
+    Shl,
+
+    /// Shift Right
+    Shr,
+
+    /// Assign value to variable
+    Assign,
+
+    /// Declare new variable with value
+    Declare,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub enum UnOpType {
+    /// Unary Negate
+    Negate,
+
+    /// Bitwise Not
+    BNot,
+
+    /// Logical Not
+    LNot,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub enum Expression {
+    /// Integer literal (64-bit)
+    I64(i64),
+    /// String literal
+    String(Rc<String>),
+    /// Variable
+    Var(String),
+    /// Binary operation. Consists of type, left hand side and right hand side
+    BinOp(BinOpType, Box<Expression>, Box<Expression>),
+    /// Unary operation. Consists of type and operand
+    UnOp(UnOpType, Box<Expression>),
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub struct Loop {
+    /// The condition that determines if the loop should continue
+    pub condition: Expression,
+    /// This is executed after each loop to advance the condition variables
+    pub advancement: Option<Expression>,
+    /// The loop body that is executed each loop
+    pub body: Ast,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub struct If {
+    /// The condition
+    pub condition: Expression,
+    /// The body that is executed when condition is true
+    pub body_true: Ast,
+    /// The if body that is executed when the condition is false
+    pub body_false: Ast,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub enum Statement {
+    Expr(Expression),
+    Loop(Loop),
+    If(If),
+    Print(Expression),
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, Default)]
+pub struct Ast {
+    pub prog: Vec<Statement>,
+}
+
+impl BinOpType {
+    /// Get the precedence for a binary operator. Higher value means the OP is stronger binding.
+    /// For example Multiplication is stronger than addition, so Mul has higher precedence than Add.
+    ///
+    /// The operator precedences are derived from the C language operator precedences. While not all
+    /// C operators are included or the exact same, the precedence oder is the same.
+    /// See: https://en.cppreference.com/w/c/language/operator_precedence
+
+    pub fn precedence(&self) -> u8 {
+        match self {
+            BinOpType::Declare => 0,
+            BinOpType::Assign => 1,
+            BinOpType::LOr => 2,
+            BinOpType::LAnd => 3,
+            BinOpType::BOr => 4,
+            BinOpType::BXor => 5,
+            BinOpType::BAnd => 6,
+            BinOpType::EquEqu | BinOpType::NotEqu => 7,
+            BinOpType::Less | BinOpType::LessEqu | BinOpType::Greater | BinOpType::GreaterEqu => 8,
+            BinOpType::Shl | BinOpType::Shr => 9,
+            BinOpType::Add | BinOpType::Sub => 10,
+            BinOpType::Mul | BinOpType::Div | BinOpType::Mod => 11,
+        }
+    }
+}

src/interpreter.rs

@@ -1,70 +1,218 @@
-use crate::parser::{Ast, BinOpType};
+use std::{fmt::Display, rc::Rc};
+
+use crate::{
+    ast::{Ast, BinOpType, Expression, If, Statement, UnOpType},
+    lexer::lex,
+    parser::parse,
+};
 
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub enum Value {
     I64(i64),
+    String(Rc<String>),
 }
 
 pub struct Interpreter {
-    // Runtime storage, for example variables ...
+    // Variable table stores the runtime values of variables
+    vartable: Vec<(String, Value)>,
 }
 
 impl Interpreter {
     pub fn new() -> Self {
-        Self {}
+        Self {
-    }
+            vartable: Vec::new(),
-
-    pub fn run(&mut self, prog: Ast) {
-        let result = self.resolve_expr(prog);
-
-        println!("Result = {:?}", result);
-    }
-
-    fn resolve_expr(&mut self, expr: Ast) -> Value {
-        match expr {
-            Ast::I64(val) => Value::I64(val),
-            Ast::BinOp(bo, lhs, rhs) => self.resolve_binop(bo, *lhs, *rhs),
         }
     }
 
-    fn resolve_binop(&mut self, bo: BinOpType, lhs: Ast, rhs: Ast) -> Value {
+    fn get_var(&self, name: &str) -> Option<Value> {
-        let lhs = self.resolve_expr(lhs);
+        self.vartable
+            .iter()
+            .rev()
+            .find(|it| it.0 == name)
+            .map(|it| it.1.clone())
+    }
+
+    fn get_var_mut(&mut self, name: &str) -> Option<&mut Value> {
+        self.vartable
+            .iter_mut()
+            .rev()
+            .find(|it| it.0 == name)
+            .map(|it| &mut it.1)
+    }
+
+    pub fn run_str(&mut self, code: &str, print_tokens: bool, print_ast: bool) {
+        let tokens = lex(code).unwrap();
+        if print_tokens {
+            println!("Tokens: {:?}", tokens);
+        }
+
+        let ast = parse(tokens);
+        if print_ast {
+            println!("{:#?}", ast);
+        }
+
+        self.run(&ast);
+    }
+
+    pub fn run(&mut self, prog: &Ast) {
+        let vartable_len = self.vartable.len();
+        for stmt in &prog.prog {
+            match stmt {
+                Statement::Expr(expr) => {
+                    self.resolve_expr(expr);
+                }
+
+                Statement::Loop(looop) => {
+                    // loop runs as long condition != 0
+                    loop {
+                        if matches!(self.resolve_expr(&looop.condition), Value::I64(0)) {
+                            break;
+                        }
+
+                        self.run(&looop.body);
+
+                        if let Some(adv) = &looop.advancement {
+                            self.resolve_expr(&adv);
+                        }
+                    }
+                }
+
+                Statement::Print(expr) => {
+                    let result = self.resolve_expr(expr);
+                    print!("{}", result);
+                }
+
+                Statement::If(If {
+                    condition,
+                    body_true,
+                    body_false,
+                }) => {
+                    if matches!(self.resolve_expr(condition), Value::I64(0)) {
+                        self.run(body_false);
+                    } else {
+                        self.run(body_true);
+                    }
+                }
+            }
+        }
+
+        self.vartable.truncate(vartable_len);
+    }
+
+    fn resolve_expr(&mut self, expr: &Expression) -> Value {
+        match expr {
+            Expression::I64(val) => Value::I64(*val),
+            Expression::String(text) => Value::String(text.clone()),
+            Expression::BinOp(bo, lhs, rhs) => self.resolve_binop(bo, lhs, rhs),
+            Expression::UnOp(uo, operand) => self.resolve_unop(uo, operand),
+            Expression::Var(name) => self.resolve_var(name),
+        }
+    }
+
+    fn resolve_var(&mut self, name: &str) -> Value {
+        match self.get_var(name) {
+            Some(val) => val.clone(),
+            None => panic!("Variable '{}' used but not declared", name),
+        }
+    }
+
+    fn resolve_unop(&mut self, uo: &UnOpType, operand: &Expression) -> Value {
+        let operand = self.resolve_expr(operand);
+
+        match (operand, uo) {
+            (Value::I64(val), UnOpType::Negate) => Value::I64(-val),
+            (Value::I64(val), UnOpType::BNot) => Value::I64(!val),
+            (Value::I64(val), UnOpType::LNot) => Value::I64(if val == 0 { 1 } else { 0 }),
+            _ => panic!("Value type is not compatible with unary operation"),
+        }
+    }
+
+    fn resolve_binop(&mut self, bo: &BinOpType, lhs: &Expression, rhs: &Expression) -> Value {
         let rhs = self.resolve_expr(rhs);
 
+        match (&bo, &lhs) {
+            (BinOpType::Declare, Expression::Var(name)) => {
+                self.vartable.push((name.clone(), rhs.clone()));
+                return rhs;
+            }
+            (BinOpType::Assign, Expression::Var(name)) => {
+                match self.get_var_mut(name) {
+                    Some(val) => *val = rhs.clone(),
+                    None => panic!("Runtime Error: Trying to assign value to undeclared variable"),
+                }
+                return rhs;
+            }
+            _ => (),
+        }
+
+        let lhs = self.resolve_expr(lhs);
+
         match (lhs, rhs) {
             (Value::I64(lhs), Value::I64(rhs)) => match bo {
                 BinOpType::Add => Value::I64(lhs + rhs),
                 BinOpType::Mul => Value::I64(lhs * rhs),
+                BinOpType::Sub => Value::I64(lhs - rhs),
+                BinOpType::Div => Value::I64(lhs / rhs),
+                BinOpType::Mod => Value::I64(lhs % rhs),
+                BinOpType::BOr => Value::I64(lhs | rhs),
+                BinOpType::BAnd => Value::I64(lhs & rhs),
+                BinOpType::BXor => Value::I64(lhs ^ rhs),
+                BinOpType::LAnd => Value::I64(if (lhs != 0) && (rhs != 0) { 1 } else { 0 }),
+                BinOpType::LOr => Value::I64(if (lhs != 0) || (rhs != 0) { 1 } else { 0 }),
+                BinOpType::Shr => Value::I64(lhs >> rhs),
+                BinOpType::Shl => Value::I64(lhs << rhs),
+                BinOpType::EquEqu => Value::I64(if lhs == rhs { 1 } else { 0 }),
+                BinOpType::NotEqu => Value::I64(if lhs != rhs { 1 } else { 0 }),
+                BinOpType::Less => Value::I64(if lhs < rhs { 1 } else { 0 }),
+                BinOpType::LessEqu => Value::I64(if lhs <= rhs { 1 } else { 0 }),
+                BinOpType::Greater => Value::I64(if lhs > rhs { 1 } else { 0 }),
+                BinOpType::GreaterEqu => Value::I64(if lhs >= rhs { 1 } else { 0 }),
+
+                BinOpType::Declare | BinOpType::Assign => unreachable!(),
             },
-            // _ => panic!("Value types are not compatible"),
+            _ => panic!("Value types are not compatible"),
+        }
+    }
+}
+
+impl Display for Value {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Value::I64(val) => write!(f, "{}", val),
+            Value::String(text) => write!(f, "{}", text),
         }
     }
 }
 
 #[cfg(test)]
 mod test {
-    use crate::parser::{Ast, BinOpType};
     use super::{Interpreter, Value};
+    use crate::ast::{BinOpType, Expression};
 
     #[test]
     fn test_interpreter_expr() {
         // Expression: 1 + 2 * 3 + 4
         // With precedence: (1 + (2 * 3)) + 4
-        let ast = Ast::BinOp(
+        let ast = Expression::BinOp(
             BinOpType::Add,
-            Ast::BinOp(
+            Expression::BinOp(
                 BinOpType::Add,
-                Ast::I64(1).into(),
+                Expression::I64(1).into(),
-                Ast::BinOp(BinOpType::Mul, Ast::I64(2).into(), Ast::I64(3).into()).into(),
+                Expression::BinOp(
+                    BinOpType::Mul,
+                    Expression::I64(2).into(),
+                    Expression::I64(3).into(),
+                )
+                .into(),
             )
             .into(),
-            Ast::I64(4).into(),
+            Expression::I64(4).into(),
         );
 
         let expected = Value::I64(11);
 
         let mut interpreter = Interpreter::new();
-        let actual = interpreter.resolve_expr(ast);
+        let actual = interpreter.resolve_expr(&ast);
 
         assert_eq!(expected, actual);
     }

src/lexer.rs

@@ -1,23 +1,31 @@
+use crate::token::Token;
+use anyhow::Result;
 use std::{iter::Peekable, str::Chars};
+use thiserror::Error;
 
-use crate::parser::BinOpType;
+#[derive(Debug, Error)]
+pub enum LexErr {
+    #[error("Failed to parse '{0}' as i64")]
+    NumericParse(String),
 
-#[derive(Debug, PartialEq, Eq)]
+    #[error("Invalid escape character '\\{0}'")]
-pub enum Token {
+    InvalidStrEscape(char),
-    /// Integer literal (64-bit)
-    I64(i64),
 
-    /// Plus (+)
+    #[error("Lexer encountered unexpected char: '{0}'")]
-    Add,
+    UnexpectedChar(char),
 
-    /// Asterisk (*)
+    #[error("Missing closing string quote '\"'")]
-    Mul,
+    MissingClosingString,
+}
 
-    /// End of file
+/// Lex the provided code into a Token Buffer
-    EoF,
+pub fn lex(code: &str) -> Result<Vec<Token>, LexErr> {
+    let mut lexer = Lexer::new(code);
+    lexer.lex()
 }
 
 struct Lexer<'a> {
+    /// The sourcecode text as an iterator over the chars
     code: Peekable<Chars<'a>>,
 }
 
@@ -27,65 +35,195 @@ impl<'a> Lexer<'a> {
         Self { code }
     }
 
-    fn lex(&mut self) -> Vec<Token> {
+    fn lex(&mut self) -> Result<Vec<Token>, LexErr> {
         let mut tokens = Vec::new();
 
-        while let Some(ch) = self.next() {
+        loop {
-            match ch {
+            match self.next() {
+                // Stop lexing at EOF
+                '\0' => break,
+
                 // Skip whitespace
-                ' ' => (),
+                ' ' | '\t' | '\n' | '\r' => (),
 
-                // Lex numbers
+                // Line comment. Consume every char until linefeed (next line)
-                '0'..='9' => {
+                '/' if matches!(self.peek(), '/') => while !matches!(self.next(), '\n' | '\0') {},
-                    let mut sval = String::from(ch);
 
-                    // Do as long as a next char exists and it is a numeric char
+                // Double character tokens
-                    while let Some('0'..='9') = self.peek() {
+                '>' if matches!(self.peek(), '>') => {
-                        // The next char is verified to be Some, so unwrap is safe
+                    self.next();
-                        sval.push(self.next().unwrap());
+                    tokens.push(Token::Shr);
-                    }
+                }
-
+                '<' if matches!(self.peek(), '<') => {
-                    // TODO: We only added numeric chars to the string, but the conversion could still fail
+                    self.next();
-                    tokens.push(Token::I64(sval.parse().unwrap()));
+                    tokens.push(Token::Shl);
+                }
+                '=' if matches!(self.peek(), '=') => {
+                    self.next();
+                    tokens.push(Token::EquEqu);
+                }
+                '!' if matches!(self.peek(), '=') => {
+                    self.next();
+                    tokens.push(Token::NotEqu);
+                }
+                '<' if matches!(self.peek(), '=') => {
+                    self.next();
+                    tokens.push(Token::LAngleEqu);
+                }
+                '>' if matches!(self.peek(), '=') => {
+                    self.next();
+                    tokens.push(Token::RAngleEqu);
+                }
+                '<' if matches!(self.peek(), '-') => {
+                    self.next();
+                    tokens.push(Token::LArrow);
+                }
+                '&' if matches!(self.peek(), '&') => {
+                    self.next();
+                    tokens.push(Token::LAnd);
+                }
+                '|' if matches!(self.peek(), '|') => {
+                    self.next();
+                    tokens.push(Token::LOr);
                 }
 
+                // Single character tokens
+                ';' => tokens.push(Token::Semicolon),
                 '+' => tokens.push(Token::Add),
+                '-' => tokens.push(Token::Sub),
                 '*' => tokens.push(Token::Mul),
+                '/' => tokens.push(Token::Div),
+                '%' => tokens.push(Token::Mod),
+                '|' => tokens.push(Token::BOr),
+                '&' => tokens.push(Token::BAnd),
+                '^' => tokens.push(Token::BXor),
+                '(' => tokens.push(Token::LParen),
+                ')' => tokens.push(Token::RParen),
+                '~' => tokens.push(Token::Tilde),
+                '<' => tokens.push(Token::LAngle),
+                '>' => tokens.push(Token::RAngle),
+                '=' => tokens.push(Token::Equ),
+                '{' => tokens.push(Token::LBraces),
+                '}' => tokens.push(Token::RBraces),
+                '!' => tokens.push(Token::LNot),
 
-                //TODO: Don't panic, keep calm
+                // Special tokens with variable length
-                _ => panic!("Lexer encountered unexpected char: '{}'", ch),
+
+                // Lex multiple characters together as numbers
+                ch @ '0'..='9' => tokens.push(self.lex_number(ch)?),
+
+                // Lex multiple characters together as a string
+                '"' => tokens.push(self.lex_str()?),
+
+                // Lex multiple characters together as identifier
+                ch @ ('a'..='z' | 'A'..='Z' | '_') => tokens.push(self.lex_identifier(ch)?),
+
+                ch => Err(LexErr::UnexpectedChar(ch))?,
             }
         }
 
-        tokens
+        Ok(tokens)
+    }
+
+    /// Lex multiple characters as a number until encountering a non numeric digit. This includes
+    /// the first character
+    fn lex_number(&mut self, first_char: char) -> Result<Token, LexErr> {
+        // String representation of the integer value
+        let mut sval = String::from(first_char);
+
+        // Do as long as a next char exists and it is a numeric char
+        loop {
+            // The next char is verified to be Some, so unwrap is safe
+            match self.peek() {
+                // Underscore is a separator, so remove it but don't add to number
+                '_' => {
+                    self.next();
+                }
+                '0'..='9' => {
+                    sval.push(self.next());
+                }
+                // Next char is not a number, so stop and finish the number token
+                _ => break,
+            }
+        }
+
+        // Try to convert the string representation of the value to i64
+        let i64val = sval.parse().map_err(|_| LexErr::NumericParse(sval))?;
+        Ok(Token::I64(i64val))
+    }
+
+    /// Lex characters as a string until encountering an unescaped closing doublequoute char '"'
+    fn lex_str(&mut self) -> Result<Token, LexErr> {
+        // Opening " was consumed in match
+
+        let mut text = String::new();
+
+        // Read all chars until encountering the closing "
+        loop {
+            match self.peek() {
+                '"' => break,
+                // If the end of file is reached while still waiting for '"', error out
+                '\0' => Err(LexErr::MissingClosingString)?,
+                _ => match self.next() {
+                    // Backshlash indicates an escaped character
+                    '\\' => match self.next() {
+                        'n' => text.push('\n'),
+                        'r' => text.push('\r'),
+                        't' => text.push('\t'),
+                        '\\' => text.push('\\'),
+                        '"' => text.push('"'),
+                        ch => Err(LexErr::InvalidStrEscape(ch))?,
+                    },
+                    // All other characters are simply appended to the string
+                    ch => text.push(ch),
+                },
+            }
+        }
+
+        // Consume closing "
+        self.next();
+
+        Ok(Token::String(text))
+    }
+
+    /// Lex characters from the text as an identifier. This includes the first character passed in
+    fn lex_identifier(&mut self, first_char: char) -> Result<Token, LexErr> {
+        let mut ident = String::from(first_char);
+
+        // Do as long as a next char exists and it is a valid char for an identifier
+        loop {
+            match self.peek() {
+                // In the middle of an identifier numbers are also allowed
+                'a'..='z' | 'A'..='Z' | '0'..='9' | '_' => {
+                    ident.push(self.next());
+                }
+                // Next char is not valid, so stop and finish the ident token
+                _ => break,
+            }
+        }
+
+        // Check for pre-defined keywords
+        let token = match ident.as_str() {
+            "loop" => Token::Loop,
+            "print" => Token::Print,
+            "if" => Token::If,
+            "else" => Token::Else,
+
+            // If it doesn't match a keyword, it is a normal identifier
+            _ => Token::Ident(ident),
+        };
+
+        Ok(token)
     }
 
     /// Advance to next character and return the removed char
-    fn next(&mut self) -> Option<char> {
+    fn next(&mut self) -> char {
-        self.code.next()
+        self.code.next().unwrap_or('\0')
     }
 
     /// Get the next character without removing it
-    fn peek(&mut self) -> Option<char> {
+    fn peek(&mut self) -> char {
-        self.code.peek().copied()
+        self.code.peek().copied().unwrap_or('\0')
-    }
-}
-
-/// Lex the provided code into a Token Buffer
-///
-/// TODO: Don't panic and implement error handling using Result
-pub fn lex(code: &str) -> Vec<Token> {
-    let mut lexer = Lexer::new(code);
-    lexer.lex()
-}
-
-impl Token {
-    pub fn try_to_binop(&self) -> Option<BinOpType> {
-        Some(match self {
-            Token::Add => BinOpType::Add,
-            Token::Mul => BinOpType::Mul,
-            _ => return None,
-        })
     }
 }
 
@@ -95,7 +233,7 @@ mod tests {
 
     #[test]
     fn test_lexer() {
-        let code = "33   +5*2  + 4456467*2334+3";
+        let code = "33   +5*2  + 4456467*2334+3 % - / << ^ | & >>";
         let expected = vec![
             Token::I64(33),
             Token::Add,
@@ -108,9 +246,17 @@ mod tests {
             Token::I64(2334),
             Token::Add,
             Token::I64(3),
+            Token::Mod,
+            Token::Sub,
+            Token::Div,
+            Token::Shl,
+            Token::BXor,
+            Token::BOr,
+            Token::BAnd,
+            Token::Shr,
         ];
 
-        let actual = lex(code);
+        let actual = lex(code).unwrap();
         assert_eq!(expected, actual);
     }
 }

src/lib.rs

@@ -1,3 +1,5 @@
 pub mod lexer;
+pub mod token;
 pub mod parser;
+pub mod ast;
 pub mod interpreter;

src/main.rs

@@ -1,23 +1,55 @@
-use nek_lang::{lexer::lex, parser::parse, interpreter::Interpreter};
+use std::{
+    env::args,
+    fs,
+    io::{stdin, stdout, Write},
+};
 
+use nek_lang::interpreter::Interpreter;
+
+#[derive(Debug, Default)]
+struct CliConfig {
+    print_tokens: bool,
+    print_ast: bool,
+    interactive: bool,
+    file: Option<String>,
+}
 
 fn main() {
+    let mut conf = CliConfig::default();
 
-    let mut code = String::new();
+    // Go through all commandline arguments except the first (filename)
-
+    for arg in args().skip(1) {
-    std::io::stdin().read_line(&mut code).unwrap();
+        match arg.as_str() {
-    let code = code.trim();
+            "--token" | "-t" => conf.print_tokens = true,
-
+            "--ast" | "-a" => conf.print_ast = true,
-    let tokens = lex(&code);
+            "--interactive" | "-i" => conf.interactive = true,
-
+            file if conf.file.is_none() => conf.file = Some(file.to_string()),
-    println!("Tokens: {:?}\n", tokens);
+            _ => panic!("Invalid argument: '{}'", arg),
-
+        }
-    let ast = parse(tokens);
+    }
-
-    println!("Ast: {:#?}\n", ast);
 
     let mut interpreter = Interpreter::new();
 
-    interpreter.run(ast);
+    if let Some(file) = &conf.file {
+        let code = fs::read_to_string(file).expect(&format!("File not found: '{}'", file));
+        interpreter.run_str(&code, conf.print_tokens, conf.print_ast);
+    }
 
+    if conf.interactive || conf.file.is_none() {
+        let mut code = String::new();
+
+        loop {
+            print!(">> ");
+            stdout().flush().unwrap();
+
+            code.clear();
+            stdin().read_line(&mut code).unwrap();
+
+            if code.trim() == "exit" {
+                break;
+            }
+
+            interpreter.run_str(&code, conf.print_tokens, conf.print_ast);
+        }
+    }
 }

src/parser.rs

@@ -1,23 +1,12 @@
 use std::iter::Peekable;
 
-use crate::lexer::Token;
+use crate::ast::*;
+use crate::token::Token;
 
-/// Types for binary operators
+/// Parse the given tokens into an abstract syntax tree
-#[derive(Debug, PartialEq, Eq, Clone)]
+pub fn parse<T: Iterator<Item = Token>, A: IntoIterator<IntoIter = T>>(tokens: A) -> Ast {
-pub enum BinOpType {
+    let mut parser = Parser::new(tokens);
-    /// Addition
+    parser.parse()
-    Add,
-
-    /// Multiplication
-    Mul,
-}
-
-#[derive(Debug, PartialEq, Eq, Clone)]
-pub enum Ast {
-    /// Integer literal (64-bit)
-    I64(i64),
-    /// Binary operation. Consists of type, left hand side and right hand side
-    BinOp(BinOpType, Box<Ast>, Box<Ast>),
 }
 
 struct Parser<T: Iterator<Item = Token>> {
@@ -31,18 +20,151 @@ impl<T: Iterator<Item = Token>> Parser<T> {
         Self { tokens }
     }
 
+    /// Parse tokens into an abstract syntax tree. This will continuously parse statements until
+    /// encountering end-of-file or a block end '}' .
     fn parse(&mut self) -> Ast {
-        self.parse_expr()
+        let mut prog = Vec::new();
+
+        loop {
+            match self.peek() {
+                Token::Semicolon => {
+                    self.next();
+                }
+                Token::EoF | Token::RBraces => break,
+
+                // By default try to lex a statement
+                _ => prog.push(self.parse_stmt()),
+            }
+        }
+
+        Ast { prog }
     }
 
-    fn parse_expr(&mut self) -> Ast {
+    /// Parse a single statement from the tokens.
+    fn parse_stmt(&mut self) -> Statement {
+        match self.peek() {
+            Token::Loop => Statement::Loop(self.parse_loop()),
+
+            Token::Print => {
+                self.next();
+
+                let expr = self.parse_expr();
+
+                // After a statement, there must be a semicolon
+                if !matches!(self.next(), Token::Semicolon) {
+                    panic!("Expected semicolon after statement");
+                }
+
+                Statement::Print(expr)
+            }
+
+            Token::If => Statement::If(self.parse_if()),
+
+            // If it is not a loop, try to lex as an expression
+            _ => {
+                let stmt = Statement::Expr(self.parse_expr());
+
+                // After a statement, there must be a semicolon
+                if !matches!(self.next(), Token::Semicolon) {
+                    panic!("Expected semicolon after statement");
+                }
+
+                stmt
+            }
+        }
+    }
+
+    /// Parse an if statement from the tokens
+    fn parse_if(&mut self) -> If {
+        if !matches!(self.next(), Token::If) {
+            panic!("Error lexing if: Expected if token");
+        }
+
+        let condition = self.parse_expr();
+
+        if !matches!(self.next(), Token::LBraces) {
+            panic!("Error lexing if: Expected '{{'")
+        }
+
+        let body_true = self.parse();
+
+        if !matches!(self.next(), Token::RBraces) {
+            panic!("Error lexing if: Expected '}}'")
+        }
+
+        let mut body_false = Ast::default();
+
+        if matches!(self.peek(), Token::Else) {
+            self.next();
+
+            if !matches!(self.next(), Token::LBraces) {
+                panic!("Error lexing if: Expected '{{'")
+            }
+
+            body_false = self.parse();
+
+            if !matches!(self.next(), Token::RBraces) {
+                panic!("Error lexing if: Expected '}}'")
+            }
+        }
+
+        If {
+            condition,
+            body_true,
+            body_false,
+        }
+    }
+
+    /// Parse a loop statement from the tokens
+    fn parse_loop(&mut self) -> Loop {
+        if !matches!(self.next(), Token::Loop) {
+            panic!("Error lexing loop: Expected loop token");
+        }
+
+        let condition = self.parse_expr();
+        let mut advancement = None;
+
+        let body;
+
+        match self.next() {
+            Token::LBraces => {
+                body = self.parse();
+            }
+
+            Token::Semicolon => {
+                advancement = Some(self.parse_expr());
+
+                if !matches!(self.next(), Token::LBraces) {
+                    panic!("Error lexing loop: Expected '{{'")
+                }
+
+                body = self.parse();
+            }
+
+            _ => panic!("Error lexing loop: Expected ';' or '{{'"),
+        }
+
+        if !matches!(self.next(), Token::RBraces) {
+            panic!("Error lexing loop: Expected '}}'")
+        }
+
+        Loop {
+            condition,
+            advancement,
+            body,
+        }
+    }
+
+    /// Parse a single expression from the tokens
+    fn parse_expr(&mut self) -> Expression {
         let lhs = self.parse_primary();
         self.parse_expr_precedence(lhs, 0)
     }
 
     /// Parse binary expressions with a precedence equal to or higher than min_prec
-    fn parse_expr_precedence(&mut self, mut lhs: Ast, min_prec: u8) -> Ast {
+    fn parse_expr_precedence(&mut self, mut lhs: Expression, min_prec: u8) -> Expression {
         while let Some(binop) = &self.peek().try_to_binop() {
+            // Stop if the next operator has a lower binding power
             if !(binop.precedence() >= min_prec) {
                 break;
             }
@@ -61,16 +183,52 @@ impl<T: Iterator<Item = Token>> Parser<T> {
                 rhs = self.parse_expr_precedence(rhs, binop.precedence() + 1);
             }
 
-            lhs = Ast::BinOp(binop, lhs.into(), rhs.into());
+            lhs = Expression::BinOp(binop, lhs.into(), rhs.into());
         }
 
         lhs
     }
 
     /// Parse a primary expression (for now only number)
-    fn parse_primary(&mut self) -> Ast {
+    fn parse_primary(&mut self) -> Expression {
         match self.next() {
-            Token::I64(val) => Ast::I64(val),
+            // Literal i64
+            Token::I64(val) => Expression::I64(val),
+
+            // Literal String
+            Token::String(text) => Expression::String(text.into()),
+
+            Token::Ident(name) => Expression::Var(name),
+
+            // Parentheses grouping
+            Token::LParen => {
+                let inner_expr = self.parse_expr();
+
+                // Verify that there is a closing parenthesis
+                if !matches!(self.next(), Token::RParen) {
+                    panic!("Error parsing primary expr: Exepected closing parenthesis ')'");
+                }
+
+                inner_expr
+            }
+
+            // Unary negation
+            Token::Sub => {
+                let operand = self.parse_primary();
+                Expression::UnOp(UnOpType::Negate, operand.into())
+            }
+
+            // Unary bitwise not (bitflip)
+            Token::Tilde => {
+                let operand = self.parse_primary();
+                Expression::UnOp(UnOpType::BNot, operand.into())
+            }
+
+            // Unary logical not
+            Token::LNot => {
+                let operand = self.parse_primary();
+                Expression::UnOp(UnOpType::LNot, operand.into())
+            }
 
             tok => panic!("Error parsing primary expr: Unexpected Token '{:?}'", tok),
         }
@@ -87,26 +245,13 @@ impl<T: Iterator<Item = Token>> Parser<T> {
     }
 }
 
-pub fn parse<T: Iterator<Item = Token>, A: IntoIterator<IntoIter = T>>(tokens: A) -> Ast {
-    let mut parser = Parser::new(tokens);
-    parser.parse()
-}
-
-impl BinOpType {
-    /// Get the precedence for a binary operator. Higher value means the OP is stronger binding.
-    /// For example Multiplication is stronger than addition, so Mul has higher precedence than Add.
-    fn precedence(&self) -> u8 {
-        match self {
-            BinOpType::Add => 0,
-            BinOpType::Mul => 1,
-        }
-    }
-}
-
 #[cfg(test)]
 mod tests {
-    use super::{parse, Ast, BinOpType};
+    use super::{parse, BinOpType, Expression};
-    use crate::lexer::Token;
+    use crate::{
+        parser::{Ast, Statement},
+        token::Token,
+    };
 
     #[test]
     fn test_parser() {
@@ -118,20 +263,30 @@ mod tests {
             Token::I64(2),
             Token::Mul,
             Token::I64(3),
-            Token::Add,
+            Token::Sub,
             Token::I64(4),
+            Token::Semicolon,
         ];
 
-        let expected = Ast::BinOp(
+        let expected = Statement::Expr(Expression::BinOp(
-            BinOpType::Add,
+            BinOpType::Sub,
-            Ast::BinOp(
+            Expression::BinOp(
                 BinOpType::Add,
-                Ast::I64(1).into(),
+                Expression::I64(1).into(),
-                Ast::BinOp(BinOpType::Mul, Ast::I64(2).into(), Ast::I64(3).into()).into(),
+                Expression::BinOp(
+                    BinOpType::Mul,
+                    Expression::I64(2).into(),
+                    Expression::I64(3).into(),
+                )
+                .into(),
             )
             .into(),
-            Ast::I64(4).into(),
+            Expression::I64(4).into(),
-        );
+        ));
+
+        let expected = Ast {
+            prog: vec![expected],
+        };
 
         let actual = parse(tokens);
         assert_eq!(expected, actual);

src/token.rs

@@ -0,0 +1,146 @@
+use crate::ast::BinOpType;
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum Token {
+    /// Integer literal (64-bit)
+    I64(i64),
+
+    /// String literal
+    String(String),
+
+    /// Identifier (name for variables, functions, ...)
+    Ident(String),
+
+    /// Loop keyword (loop)
+    Loop,
+
+    /// Print keyword (print)
+    Print,
+
+    /// If keyword (if)
+    If,
+
+    /// Else keyword (else)
+    Else,
+
+    /// Left Parenthesis ('(')
+    LParen,
+
+    /// Right Parenthesis (')')
+    RParen,
+
+    /// Left curly braces ({)
+    LBraces,
+
+    /// Right curly braces (})
+    RBraces,
+
+    /// Plus (+)
+    Add,
+
+    /// Minus (-)
+    Sub,
+
+    /// Asterisk (*)
+    Mul,
+
+    /// Slash (/)
+    Div,
+
+    /// Percent (%)
+    Mod,
+
+    /// Equal Equal (==)
+    EquEqu,
+
+    /// Exclamationmark Equal (!=)
+    NotEqu,
+
+    /// Pipe (|)
+    BOr,
+
+    /// Ampersand (&)
+    BAnd,
+
+    /// Circumflex (^)
+    BXor,
+
+    /// Logical AND (&&)
+    LAnd,
+
+    /// Logical OR (||)
+    LOr,
+
+    /// Shift Left (<<)
+    Shl,
+
+    /// Shift Right (>>)
+    Shr,
+
+    /// Tilde (~)
+    Tilde,
+
+    /// Logical not (!)
+    LNot,
+
+    /// Left angle bracket (<)
+    LAngle,
+
+    /// Right angle bracket (>)
+    RAngle,
+
+    /// Left angle bracket Equal (<=)
+    LAngleEqu,
+
+    /// Left angle bracket Equal (>=)
+    RAngleEqu,
+
+    /// Left arrow (<-)
+    LArrow,
+
+    /// Equal Sign (=)
+    Equ,
+
+    /// Semicolon (;)
+    Semicolon,
+
+    /// End of file
+    EoF,
+}
+
+impl Token {
+    pub fn try_to_binop(&self) -> Option<BinOpType> {
+        Some(match self {
+            Token::Add => BinOpType::Add,
+            Token::Sub => BinOpType::Sub,
+
+            Token::Mul => BinOpType::Mul,
+            Token::Div => BinOpType::Div,
+            Token::Mod => BinOpType::Mod,
+
+            Token::BAnd => BinOpType::BAnd,
+            Token::BOr => BinOpType::BOr,
+            Token::BXor => BinOpType::BXor,
+
+            Token::LAnd => BinOpType::LAnd,
+            Token::LOr => BinOpType::LOr,
+
+            Token::Shl => BinOpType::Shl,
+            Token::Shr => BinOpType::Shr,
+
+            Token::EquEqu => BinOpType::EquEqu,
+            Token::NotEqu => BinOpType::NotEqu,
+
+            Token::LAngle => BinOpType::Less,
+            Token::LAngleEqu => BinOpType::LessEqu,
+
+            Token::RAngle => BinOpType::Greater,
+            Token::RAngleEqu => BinOpType::GreaterEqu,
+
+            Token::LArrow => BinOpType::Declare,
+            Token::Equ => BinOpType::Assign,
+
+            _ => return None,
+        })
+    }
+}