restructure parsing and typing modules

* parsing backend submodules
* move typing to its own module

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "kronec"
-version = "0.1.0"
+version = "0.0.1"
 edition = "2021"
 
 [dependencies]

src/ast/expr.rs

@@ -4,10 +4,15 @@ use crate::ast::*;
 pub enum Expr {
     BinaryExpression(Box<Expr>, BinaryOperator, Box<Expr>),
     Identifier(Identifier),
+    Call(Box<Call>),
+    // Literals
+    BooleanLiteral(bool),
     IntegerLiteral(i64),
     FloatLiteral(f64),
     StringLiteral(String),
-    Call(Box<Call>),
+    Block(Box<Block>),
+    /// Last field is either Expr::Block or Expr::IfExpr
+    IfExpr(Box<Expr>, Box<Block>, Box<Expr>),
 }
 
 #[derive(Debug, PartialEq, Clone)]
@@ -16,4 +21,7 @@ pub enum BinaryOperator {
     Sub,
     Mul,
     Div,
+    Modulo,
+    Equal,
+    NotEqual,
 }

src/ast/mod.rs

@@ -1,17 +1,29 @@
 pub mod expr;
-pub mod typ;
+pub mod module;
+
+use std::path::Path;
 
 pub use crate::ast::expr::{BinaryOperator, Expr};
-pub use crate::ast::typ::*;
+use crate::ast::module::*;
+use crate::typing::Type;
+
+pub type Identifier = String;
 
 // XXX: Is this enum actually useful? Is 3:30 AM btw
 #[derive(Debug, PartialEq)]
 pub enum Ast {
+    Module(Module),
+}
+
+#[derive(Debug, PartialEq)]
+pub enum Definition {
     FunctionDefinition(FunctionDefinition),
-    Expr(Expr),
-    Module(Vec<Ast>),
-    Block(Block),
-    Statement(Statement),
+    //StructDefinition(StructDefinition),
+}
+
+#[derive(Debug, PartialEq)]
+pub struct Location {
+    pub file: Box<Path>,
 }
 
 #[derive(Debug, PartialEq)]
@@ -20,6 +32,7 @@ pub struct FunctionDefinition {
     pub parameters: Vec<Parameter>,
     pub return_type: Option<Type>,
     pub body: Box<Block>,
+    pub line_col: (usize, usize),
 }
 
 #[derive(Debug, PartialEq)]
@@ -30,9 +43,13 @@ pub struct Block {
 
 #[derive(Debug, PartialEq)]
 pub enum Statement {
+    DeclareStatement(Identifier, Expr),
     AssignStatement(Identifier, Expr),
     ReturnStatement(Option<Expr>),
     CallStatement(Call),
+    UseStatement(ModulePath),
+    IfStatement(Expr, Block),
+    WhileStatement(Box<Expr>, Box<Block>),
 }
 
 #[derive(Debug, PartialEq)]
@@ -41,31 +58,9 @@ pub struct Call {
     pub args: Vec<Expr>,
 }
 
-pub type Identifier = String;
-
 #[derive(Debug, PartialEq)]
 pub struct Parameter {
     pub name: Identifier,
     pub typ: Type,
 }
 
-impl Ast {
-    /// Type checks the AST and add missing return types.
-    pub fn check_return_types(&mut self) -> Result<(), TypeError> {
-        match self {
-            Ast::Module(defs) => {
-                for def in defs {
-                    if let Ast::FunctionDefinition { .. } = def {
-                        def.check_return_types()?;
-                    }
-                }
-            }
-            Ast::FunctionDefinition(func) => {
-                let typ = func.typ(&mut TypeContext::default())?;
-                func.return_type = Some(typ.clone());
-            }
-            _ => unreachable!(),
-        }
-        Ok(())
-    }
-}

src/ast/module.rs

@@ -0,0 +1,66 @@
+use std::path::Path;
+use super::Definition;
+
+#[derive(Debug, PartialEq, Clone)]
+pub struct ModulePath {
+    components: Vec<String>,
+}
+
+impl std::fmt::Display for ModulePath {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_fmt(format_args!("{}", self.components.join("::")))
+    }
+}
+
+impl From<&Path> for ModulePath {
+    fn from(path: &Path) -> Self {
+        let meta = std::fs::metadata(path).unwrap();
+        ModulePath {
+            components: path
+                .components()
+                .map(|component| match component {
+                    std::path::Component::Normal(n) => {
+                        if meta.is_file() {
+                            n.to_str().unwrap().split(".").nth(0).unwrap().to_string()
+                        } else if meta.is_dir() {
+                            n.to_str().unwrap().to_string()
+                        } else {
+                            // XXX: symlinks?
+                            unreachable!()
+                        }
+                    }
+                    _ => unreachable!(),
+                })
+                .collect(),
+        }
+    }
+}
+
+impl From<&str> for ModulePath {
+    fn from(string: &str) -> Self {
+        ModulePath {
+            components: string.split("::").map(|c| c.to_string()).collect(),
+        }
+    }
+}
+
+type ImportPath = ModulePath;
+
+#[derive(Debug, PartialEq)]
+pub struct Module {
+    pub file: Option<std::path::PathBuf>,
+    pub path: ModulePath,
+    pub definitions: Vec<Definition>,
+    pub imports: Vec<ImportPath>,
+}
+
+impl Module {
+    pub fn new(path: ModulePath) -> Self {
+        Module {
+            path,
+            file: None,
+            definitions: vec![],
+            imports: vec![],
+        }
+    }
+}

src/ast/typ.rs

@@ -1,158 +0,0 @@
-use std::collections::HashMap;
-
-use crate::ast::*;
-
-#[derive(Debug, PartialEq, Clone)]
-pub enum Type {
-    Int,
-    Float,
-    Unit,
-    Str,
-    Custom(Identifier),
-}
-
-impl From<&str> for Type {
-    fn from(value: &str) -> Self {
-        match value {
-            "int" => Type::Int,
-            "float" => Type::Float,
-            _ => Type::Custom(Identifier::from(value)),
-        }
-    }
-}
-
-#[derive(Debug)]
-pub enum TypeError {
-    InvalidBinaryOperator {
-        operator: BinaryOperator,
-        lht: Type,
-        rht: Type,
-    },
-    BlockTypeDoesNotMatchFunctionType {
-        function_name: String,
-        function_type: Type,
-        block_type: Type,
-    },
-    ReturnTypeDoesNotMatchFunctionType {
-        function_name: String,
-        function_type: Type,
-        ret_type: Type,
-    },
-    UnknownIdentifier {
-        identifier: String,
-    },
-}
-
-#[derive(Default)]
-pub struct TypeContext {
-    pub function: Option<Identifier>,
-    pub variables: HashMap<Identifier, Type>,
-}
-
-/// Trait for nodes which have a deducible type.
-pub trait Typ {
-    /// Try to resolve the type of the node.
-    fn typ(&self, ctx: &mut TypeContext) -> Result<Type, TypeError>;
-}
-
-impl Typ for FunctionDefinition {
-    fn typ(&self, ctx: &mut TypeContext) -> Result<Type, TypeError> {
-        let func = self;
-
-        let mut ctx = TypeContext {
-            function: Some(func.name.clone()),
-            ..Default::default()
-        };
-        for param in &func.parameters {
-            ctx.variables.insert(param.name.clone(), param.typ.clone());
-        }
-
-        let body_type = &func.body.typ(&mut ctx)?;
-
-        // If the return type is not specified, it is unit.
-        let func_return_type = match &func.return_type {
-            Some(typ) => typ,
-            None => &Type::Unit,
-        };
-
-        // Check coherence with the body's type.
-        if *func_return_type != *body_type {
-            return Err(TypeError::BlockTypeDoesNotMatchFunctionType {
-                function_name: func.name.clone(),
-                function_type: func_return_type.clone(),
-                block_type: body_type.clone(),
-            })
-        }
-
-        // Check coherence with return statements.
-        for statement in &func.body.statements {
-            if let Statement::ReturnStatement(value) = statement {
-                let ret_type = match value {
-                    Some(expr) => expr.typ(&mut ctx)?,
-                    None => Type::Unit,
-                };
-                if ret_type != *func_return_type {
-                    return Err(TypeError::ReturnTypeDoesNotMatchFunctionType {
-                        function_name: func.name.clone(),
-                        function_type: func_return_type.clone(),
-                        ret_type,
-                    })
-                }
-            }
-        }
-
-        Ok(func_return_type.clone())
-    }
-}
-
-impl Typ for Block {
-    fn typ(&self, ctx: &mut TypeContext) -> Result<Type, TypeError> {
-        // Check if there is an expression at the end of the block.
-        if let Some(expr) = &self.value {
-            expr.typ(ctx)
-        } else {
-            Ok(Type::Unit)
-        }
-    }
-}
-
-impl Typ for Expr {
-    fn typ(&self, ctx: &mut TypeContext) -> Result<Type, TypeError> {
-        match self {
-            Expr::Identifier(identifier) => {
-                if let Some(typ) = ctx.variables.get(identifier) {
-                    Ok(typ.clone())
-                } else {
-                    Err(TypeError::UnknownIdentifier {
-                        identifier: identifier.clone(),
-                    })
-                }
-            }
-            Expr::IntegerLiteral(_) => Ok(Type::Int),
-            Expr::FloatLiteral(_) => Ok(Type::Float),
-            Expr::BinaryExpression(lhs, op, rhs) => match op {
-                BinaryOperator::Add
-                | BinaryOperator::Sub
-                | BinaryOperator::Mul
-                | BinaryOperator::Div => {
-                    let left_type = &lhs.typ(ctx)?;
-                    let right_type = &rhs.typ(ctx)?;
-                    match (left_type, right_type) {
-                        (Type::Int, Type::Int) => Ok(Type::Int),
-                        (Type::Float, Type::Int | Type::Float) => Ok(Type::Float),
-                        (Type::Int, Type::Float) => Ok(Type::Float),
-                        (_, _) => Err(TypeError::InvalidBinaryOperator {
-                            operator: op.clone(),
-                            lht: left_type.clone(),
-                            rht: right_type.clone(),
-                        }),
-                    }
-                }
-            },
-            Expr::StringLiteral(_) => Ok(Type::Str),
-            Expr::Call(call) => {
-                todo!("resolve call type using ctx");
-            }
-        }
-    }
-}

src/main.rs

@@ -1,8 +1,10 @@
 mod ast;
 mod parsing;
+mod typing;
 
 use clap::{Parser, Subcommand};
-use std::fs;
+
+use crate::ast::module::Module;
 
 /// Experimental compiler for krone
 #[derive(Parser, Debug)]
@@ -16,8 +18,8 @@ struct Cli {
 #[derive(Subcommand, Debug)]
 enum Commands {
     Parse {
-        /// Path to the source file
-        file: String,
+        /// Path to the source files
+        files: Vec<String>,
 
         /// Dump the AST to stdout
         #[arg(long)]
@@ -25,7 +27,7 @@ enum Commands {
 
         /// Add missing return types in the AST
         #[arg(long)]
-        complete_ast: bool,
+        type_check: bool,
     },
 }
 
@@ -34,25 +36,31 @@ fn main() {
 
     match &cli.command {
         Commands::Parse {
-            file,
+            files,
             dump_ast,
-            complete_ast,
+            type_check,
         } => {
-            let source = fs::read_to_string(&file).expect("could not read the source file");
-            let mut ast = match parsing::parse(&source) {
-                Ok(ast) => ast,
+            let paths = files.iter().map(std::path::Path::new);
+            let modules: Vec<Module> = paths
+                .map(|path| match parsing::parse_file(&path) {
+                    Ok(module) => module,
                     Err(e) => panic!("Parsing error: {:#?}", e),
-            };
+                })
+                .collect();
 
-            if *complete_ast {
-                if let Err(e) = ast.check_return_types() {
-                    eprintln!("{:#?}", e);
+            if *type_check {
+                for module in &modules {
+                    if let Err(e) = module.type_check() {
+                        eprintln!("{}", e);
                         return;
                     }
                 }
+            }
 
             if *dump_ast {
-                println!("{:#?}", &ast);
+                for module in &modules {
+                    println!("{:#?}", &module);
+                }
                 return;
             }
 

src/parsing/backend/handmade/lex.rs

@@ -0,0 +1,157 @@
+use std::iter::Peekable;
+use std::str::Chars;
+
+#[derive(Debug)]
+pub enum Token {
+    LeftBracket,
+    RightBracket,
+    If,
+    Else,
+    Identifier(String),
+    LeftParenthesis,
+    RightParenthesis,
+    Func,
+    Colon,
+    While,
+    Set,
+    LineComment,
+    Mul,
+    Sub,
+    Add,
+    Slash,
+    Modulo,
+    NotEqual,
+    Equal,
+    DoubleEquals,
+    Exclamation,
+    NumberLiteral,
+}
+
+#[derive(Debug)]
+pub enum TokenError {
+    InvalidToken,
+}
+
+pub struct Lexer {
+    line: usize,
+    column: usize,
+}
+
+impl Lexer {
+    pub fn new() -> Self {
+        Self { line: 1, column: 1 }
+    }
+
+    pub fn tokenize(&mut self, input: String) -> Result<Vec<Token>, TokenError> {
+        let mut tokens: Vec<Token> = Vec::new();
+        let mut chars = input.chars().peekable();
+        while let Some(tok_or_err) = self.get_next_token(&mut chars) {
+            match tok_or_err {
+                Ok(token) => tokens.push(token),
+                Err(err) => return Err(err),
+            };
+        }
+        Ok(tokens)
+    }
+
+    fn get_next_token(&mut self, chars: &mut Peekable<Chars>) -> Option<Result<Token, TokenError>> {
+        if let Some(ch) = chars.next() {
+            let tok_or_err = match ch {
+                '(' => Ok(Token::LeftParenthesis),
+                ')' => Ok(Token::RightParenthesis),
+                '{' => Ok(Token::LeftBracket),
+                '}' => Ok(Token::RightBracket),
+                '+' => Ok(Token::Add),
+                '-' => Ok(Token::Sub),
+                '*' => Ok(Token::Mul),
+                '%' => Ok(Token::Modulo),
+                '/' => {
+                    if let Some('/') = chars.peek() {
+                        chars.next();
+                        let comment = chars.take_while(|c| c != &'\n');
+                        self.column += comment.count() + 1;
+                        Ok(Token::LineComment)
+                    } else {
+                        Ok(Token::Slash)
+                    }
+                }
+                '=' => {
+                    if let Some(ch2) = chars.peek() {
+                        match ch2 {
+                            '=' => {
+                                chars.next();
+                                self.column += 1;
+                                Ok(Token::DoubleEquals)
+                            }
+                            ' ' => Ok(Token::Equal),
+                            _ => Err(TokenError::InvalidToken),
+                        }
+                    } else {
+                        Ok(Token::Equal)
+                    }
+                }
+                '!' => {
+                    if let Some(ch2) = chars.next() {
+                        match ch2 {
+                            '=' => {
+                                self.column += 1;
+                                Ok(Token::NotEqual)
+                            }
+                            _ => Err(TokenError::InvalidToken),
+                        }
+                    } else {
+                        Ok(Token::Exclamation)
+                    }
+                }
+                'a'..='z' | 'A'..='Z' => {
+                    let mut word = String::from(ch);
+                    while let Some(ch2) = chars.peek() {
+                        if ch2.is_alphanumeric() {
+                            if let Some(ch2) = chars.next() {
+                                word.push(ch2);
+                            }
+                        } else {
+                            break;
+                        }
+                    }
+                    self.column += word.len();
+                    match word.as_str() {
+                        "func" => Ok(Token::Func),
+                        "if" => Ok(Token::If),
+                        "else" => Ok(Token::Else),
+                        "set" => Ok(Token::Set),
+                        "while" => Ok(Token::While),
+                        _ => Ok(Token::Identifier(word)),
+                    }
+                }
+                '0'..='9' | '.' => {
+                    let word = chars
+                        .take_while(|c| c.is_numeric() || c == &'.')
+                        .collect::<String>();
+                    self.column += word.len();
+                    // XXX: handle syntax error in number literals
+                    Ok(Token::NumberLiteral)
+                }
+                ':' => Ok(Token::Colon),
+                '\n' => {
+                    self.line += 1;
+                    self.column = 1;
+                    return self.get_next_token(chars);
+                }
+                ' ' => {
+                    self.column += 1;
+                    return self.get_next_token(chars);
+                }
+                '\t' => {
+                    self.column += 8;
+                    return self.get_next_token(chars);
+                }
+                _ => Err(TokenError::InvalidToken),
+            };
+            self.column += 1;
+            Some(tok_or_err)
+        } else {
+            None
+        }
+    }
+}

src/parsing/backend/handmade/mod.rs

@@ -0,0 +1,149 @@
+// In progress parser from scratch
+
+use crate::lex::Token;
+use std::cell::RefCell;
+use std::rc::Rc;
+
+#[derive(Debug)]
+pub enum NodeType {
+    Document, // This is the root node
+    LineComment,
+    FunctionDefinition,
+    FunctionParam,
+    VariableName(String),
+    Type(String),
+}
+
+use NodeType::*;
+
+pub struct Node {
+    kind: NodeType,
+    parent: Option<Rc<RefCell<Node>>>,
+    children: Vec<Box<Node>>,
+}
+
+impl Node {
+    fn new() -> Self {
+        Node::default()
+    }
+
+    fn with_kind(&mut self, kind: NodeType) -> &mut Self {
+        self.kind = kind;
+        self
+    }
+
+    fn with_children(&mut self, children: Vec<Node>) -> &mut Self {
+        for child in children {
+            self.push_child(child);
+        }
+        self
+    }
+
+    fn push_child(&mut self, mut child: Node) {
+        child.parent = Some(Rc::new(RefCell::new(*self)));
+        self.children.push(Box::new(child));
+    }
+
+    pub fn print_tree(&self) {
+        self.print_tree_rec(0);
+    }
+
+    fn print_tree_rec(&self, indent: u8) {
+        for _ in 1..=indent {
+            print!(" ");
+        }
+        println!("{:?}", self.kind);
+        for child in &self.children {
+            child.print_tree_rec(indent + 2);
+        }
+    }
+}
+
+impl Default for Node {
+    fn default() -> Self {
+        Node {
+            kind: Document,
+            parent: None,
+            children: Vec::new(),
+        }
+    }
+}
+
+impl From<NodeType> for Node {
+    fn from(value: NodeType) -> Self {
+        Node {
+            kind: value,
+            ..Node::default()
+        }
+    }
+}
+
+#[derive(Debug)]
+pub enum SyntaxError {
+    FuncExpectedIdentifier,
+    FuncExpectedLeftParenthesisAfterIdentifier,
+    UnexpectedToken,
+}
+
+pub struct Parser {}
+
+impl Parser {
+    pub fn new() -> Self {
+        Parser {}
+    }
+
+    pub fn parse_tokens(&mut self, tokens: Vec<Token>) -> Result<Node, SyntaxError> {
+        let mut tokens = tokens.iter().peekable();
+        let mut root_node = Node::new();
+
+        while let Some(token) = tokens.next() {
+            let node_or_err = match token {
+                Token::LineComment => Ok(Node {
+                    kind: LineComment,
+                    ..Node::default()
+                }),
+
+                Token::Func => {
+                    let identifier = if let Some(ident) = tokens.next() {
+                        match ident {
+                            Token::Identifier(id) => Some(id),
+                            _ => return Err(SyntaxError::FuncExpectedIdentifier),
+                        }
+                    } else {
+                        None
+                    };
+
+                    if let Some(Token::LeftParenthesis) = tokens.next() {
+                    } else {
+                        return Err(SyntaxError::FuncExpectedLeftParenthesisAfterIdentifier);
+                    };
+
+                    let mut params: Vec<Node> = Vec::new();
+                    while let Some(Token::Identifier(_)) = tokens.peek() {
+                        if let Some(Token::Identifier(param_name)) = tokens.next() {
+                            if let Some(Token::Colon) = tokens.next() {
+                                if let Some(Token::Identifier(type_name)) = tokens.next() {
+                                    let mut node =
+                                        Node::new().with_kind(FunctionParam).with_children(vec![
+                                            VariableName(param_name.into()).into(),
+                                            Type(type_name.into()).into(),
+                                        ]);
+                                    params.push(*node);
+                                }
+                            }
+                        }
+                    }
+                    let node = Node::from(NodeType::FunctionDefinition).with_children(params);
+                    Ok(*node)
+                }
+
+                _ => Err(SyntaxError::UnexpectedToken),
+            };
+            if let Ok(node) = node_or_err {
+                root_node.push_child(node);
+            } else {
+            };
+        }
+        Ok(root_node)
+    }
+}

src/parsing/backend/mod.rs

@@ -0,0 +1 @@
+pub mod pest;

src/parsing/backend/pest/grammar.pest

@@ -0,0 +1,70 @@
+// This file is just a little test of pest.rs
+
+source_file  = { SOI ~ module_items ~ EOI }
+module_items = { (use_statement | definition)* }
+
+// Statements
+statement         = { assign_statement | declare_statement | return_statement | call_statement | use_statement | while_statement | if_statement }
+declare_statement = { ident ~ "=" ~ expr ~ ";" }
+assign_statement  = { "set" ~ ident ~ "=" ~ expr ~ ";" }
+return_statement  = { "return" ~ expr? ~ ";" }
+call_statement    = { call ~ ";" }
+use_statement     = { "use" ~ import_path ~ ";" }
+while_statement   = { "while" ~ expr ~ block ~ ";" }
+if_statement      = { if_branch ~ ("else" ~ (if_branch | block))? ~ ";" }
+
+if_branch = _{ "if" ~ expr ~ block }
+
+// Module paths
+import_path = { ident ~ ("::" ~ ident)* }
+
+// Function call
+call = { ident ~ "(" ~ args ~ ")" }
+args = { (expr ~ ",")* ~ expr? }
+
+definition = { func_def }
+
+// Function definition
+func_def   = { "fn" ~ ident ~ "(" ~ parameters ~ ")" ~ typ? ~ block }
+parameters = {
+    (parameter ~ ",")* ~ (parameter)?
+}
+parameter  = { ident ~ ":" ~ typ }
+
+// Operators
+infix     = _{ add | subtract | multiply | divide | not_equal | equal | modulo }
+add       =  { "+" }
+subtract  =  { "-" }
+multiply  =  { "*" }
+divide    =  { "/" }
+modulo    =  { "%" }
+equal     =  { "==" }
+not_equal =  { "!=" }
+
+prefix = _{ not }
+not    =  { "!" }
+
+// Expressions
+expr    =  { prefix? ~ atom ~ (infix ~ prefix? ~ atom)* }
+atom    = _{ call | if_expr | block | literal | ident | "(" ~ expr ~ ")" }
+block   =  { "{" ~ statement* ~ expr? ~ "}" }
+if_expr =  { "if" ~ expr ~ block ~ "else" ~ (block | if_expr) }
+
+ident = @{ (ASCII_ALPHANUMERIC | "_")+ }
+typ   = _{ ident }
+
+// Literals
+literal         = _{ boolean_literal | float_literal | integer_literal | string_literal }
+boolean_literal = @{ "true" | "false" }
+string_literal  = ${ "\"" ~ string_content ~ "\"" }
+string_content  = @{ char* }
+char            =  {
+    !("\"" | "\\") ~ ANY
+  | "\\" ~ ("\"" | "\\" | "/" | "b" | "f" | "n" | "r" | "t")
+  | "\\" ~ ("u" ~ ASCII_HEX_DIGIT{4})
+}
+integer_literal = @{ ASCII_DIGIT+ }
+float_literal   = @{ ("0" | ASCII_NONZERO_DIGIT ~ ASCII_DIGIT*) ~ "." ~ ASCII_DIGIT* }
+
+WHITESPACE = _{ " " | "\n" | "\t" }
+COMMENT    = _{ "//" ~ (!NEWLINE ~ ANY)* }

src/parsing/backend/pest/mod.rs

@@ -1,15 +1,20 @@
-use lazy_static;
+use std::fs;
+use std::path::Path;
+
 use pest::error::Error;
 use pest::iterators::Pair;
 use pest::pratt_parser::PrattParser;
 use pest::Parser;
 
+use crate::ast::module::{Module, ModulePath};
 use crate::ast::*;
+use crate::typing::Type;
 
 #[derive(pest_derive::Parser)]
-#[grammar = "parsing/grammar.pest"]
+#[grammar = "parsing/backend/pest/grammar.pest"]
 struct KrParser;
 
+use lazy_static;
 lazy_static::lazy_static! {
     static ref PRATT_PARSER: PrattParser<Rule> = {
         use pest::pratt_parser::{Assoc::*, Op};
@@ -17,36 +22,51 @@ lazy_static::lazy_static! {
 
         // Precedence is defined lowest to highest
         PrattParser::new()
-            // Addition and subtract have equal precedence
+            .op(Op::infix(equal, Left) | Op::infix(not_equal, Left))
             .op(Op::infix(add, Left) | Op::infix(subtract, Left))
+            .op(Op::infix(modulo, Left))
             .op(Op::infix(multiply, Left) | Op::infix(divide, Left))
     };
 }
 
-pub fn parse(source: &str) -> Result<Ast, Error<Rule>> {
-    let mut definitions: Vec<Ast> = vec![];
+pub fn parse_file(path: &Path) -> Result<Module, Error<Rule>> {
+    let source = fs::read_to_string(&path).expect("could not read source file");
+    let module_path = ModulePath::from(path);
+    let mut module = parse_as_module(&source, module_path)?;
+    module.file = Some(path.to_owned());
+    Ok(module)
+}
+
+pub fn parse_as_module(source: &str, path: ModulePath) -> Result<Module, Error<Rule>> {
+    let mut pairs = KrParser::parse(Rule::source_file, &source)?;
+
+    assert!(pairs.len() == 1);
+    let module = parse_module(pairs.next().unwrap().into_inner().next().unwrap(), path);
+
+    Ok(module)
+}
+
+pub fn parse_module(pair: Pair<Rule>, path: ModulePath) -> Module {
+    assert!(pair.as_rule() == Rule::module_items);
+
+    let mut module = Module::new(path);
 
-    let pairs = KrParser::parse(Rule::source_file, source)?;
-    for pair in pairs {
-        match pair.as_rule() {
-            Rule::source_file => {
     let pairs = pair.into_inner();
     for pair in pairs {
         match pair.as_rule() {
             Rule::definition => {
-                            let definition = parse_definition(pair.into_inner().next().unwrap());
-                            definitions.push(definition);
+                let def = parse_definition(pair.into_inner().next().unwrap());
+                module.definitions.push(def);
+            }
+            Rule::use_statement => {
+                let path = parse_import_path(pair.into_inner().next().unwrap());
+                module.imports.push(path);
             }
-                        Rule::EOI => {}
             _ => panic!("unexpected rule in source_file: {:?}", pair.as_rule()),
         }
     }
-            }
-            _ => eprintln!("unexpected top-level rule {:?}", pair.as_rule()),
-        }
-    }
 
-    Ok(Ast::Module(definitions))
+    module
 }
 
 fn parse_block(pair: Pair<Rule>) -> Block {
@@ -73,6 +93,12 @@ fn parse_statement(pair: Pair<Rule>) -> Statement {
             let expr = parse_expression(pairs.next().unwrap());
             Statement::AssignStatement(identifier, expr)
         }
+        Rule::declare_statement => {
+            let mut pairs = pair.into_inner();
+            let identifier = pairs.next().unwrap().as_str().to_string();
+            let expr = parse_expression(pairs.next().unwrap());
+            Statement::DeclareStatement(identifier, expr)
+        }
         Rule::return_statement => {
             let expr = if let Some(pair) = pair.into_inner().next() {
                 Some(parse_expression(pair))
@@ -85,10 +111,32 @@ fn parse_statement(pair: Pair<Rule>) -> Statement {
             let call = parse_call(pair.into_inner().next().unwrap());
             Statement::CallStatement(call)
         }
+        Rule::use_statement => {
+            let path = parse_import_path(pair.into_inner().next().unwrap());
+            Statement::UseStatement(path)
+        }
+        Rule::if_statement => {
+            let mut pairs = pair.into_inner();
+            let condition = parse_expression(pairs.next().unwrap());
+            let block = parse_block(pairs.next().unwrap());
+            Statement::IfStatement(condition, block)
+        }
+        Rule::while_statement => {
+            let mut pairs = pair.into_inner();
+            let condition = parse_expression(pairs.next().unwrap());
+            let block = parse_block(pairs.next().unwrap());
+            Statement::WhileStatement(Box::new(condition), Box::new(block))
+        }
         _ => unreachable!("unexpected rule '{:?}' in parse_statement", pair.as_rule()),
     }
 }
 
+type ImportPath = ModulePath;
+
+fn parse_import_path(pair: Pair<Rule>) -> ImportPath {
+    ModulePath::from(pair.as_str())
+}
+
 fn parse_call(pair: Pair<Rule>) -> Call {
     let mut pairs = pair.into_inner();
     // TODO: support calls on more than identifiers (needs grammar change)
@@ -117,9 +165,26 @@ fn parse_expression(pair: Pair<Rule>) -> Expr {
                     .parse()
                     .unwrap(),
             ),
-            Rule::ident => Expr::Identifier(primary.as_str().to_string()),
             Rule::expr => parse_expression(primary),
+            Rule::ident => Expr::Identifier(primary.as_str().to_string()),
             Rule::call => Expr::Call(Box::new(parse_call(primary))),
+            Rule::block => Expr::Block(Box::new(parse_block(primary))),
+            Rule::if_expr => {
+                let mut pairs = primary.into_inner();
+                let condition = parse_expression(pairs.next().unwrap());
+                let true_block = parse_block(pairs.next().unwrap());
+                let else_value = parse_expression(pairs.next().unwrap());
+                Expr::IfExpr(
+                    Box::new(condition),
+                    Box::new(true_block),
+                    Box::new(else_value),
+                )
+            }
+            Rule::boolean_literal => Expr::BooleanLiteral(match primary.as_str() {
+                "true" => true,
+                "false" => false,
+                _ => unreachable!(),
+            }),
             _ => unreachable!(
                 "Unexpected rule '{:?}' in primary expression",
                 primary.as_rule()
@@ -131,6 +196,9 @@ fn parse_expression(pair: Pair<Rule>) -> Expr {
                 Rule::subtract => BinaryOperator::Sub,
                 Rule::multiply => BinaryOperator::Mul,
                 Rule::divide => BinaryOperator::Div,
+                Rule::modulo => BinaryOperator::Modulo,
+                Rule::equal => BinaryOperator::Equal,
+                Rule::not_equal => BinaryOperator::NotEqual,
                 _ => unreachable!(),
             };
             Expr::BinaryExpression(Box::new(lhs), operator, Box::new(rhs))
@@ -141,14 +209,15 @@ fn parse_expression(pair: Pair<Rule>) -> Expr {
 fn parse_parameter(pair: Pair<Rule>) -> Parameter {
     assert!(pair.as_rule() == Rule::parameter);
     let mut pair = pair.into_inner();
-    let name: String = pair.next().unwrap().as_str().to_string();
+    let name = pair.next().unwrap().as_str().to_string();
     let typ = Type::from(pair.next().unwrap().as_str());
     Parameter { name, typ }
 }
 
-fn parse_definition(pair: Pair<Rule>) -> Ast {
+fn parse_definition(pair: Pair<Rule>) -> Definition {
     match pair.as_rule() {
         Rule::func_def => {
+            let line_col = pair.line_col();
             let mut pairs = pair.into_inner();
             let name = pairs.next().unwrap().as_str().to_string();
             let parameters: Vec<Parameter> = pairs
@@ -169,11 +238,12 @@ fn parse_definition(pair: Pair<Rule>) -> Ast {
             };
             let body = parse_block(pair);
             let body = Box::new(body);
-            Ast::FunctionDefinition(FunctionDefinition {
+            Definition::FunctionDefinition(FunctionDefinition {
                 name,
                 parameters,
                 return_type,
                 body,
+                line_col,
             })
         }
         _ => panic!("unexpected node for definition: {:?}", pair.as_rule()),

src/parsing/backend/tree_sitter/lib.rs

@@ -0,0 +1,222 @@
+use tree_sitter::{self, Language, Parser, TreeCursor};
+
+enum Ast {
+    FuncDef(FuncDef),
+    Expr(Expr),
+    Module(Vec<Ast>),
+    Block(Vec<Statement>, Option<Expr>),
+    Statement(Statement),
+}
+
+enum BinaryOperator {
+    Add,
+    Sub,
+    Mul,
+    Div,
+}
+
+enum Expr {
+    BinaryExpression(Box<Expr>, BinaryOperator, Box<Expr>),
+}
+
+enum Statement {
+    AssignStatement(Identifier, Expr),
+}
+
+type Identifier = String;
+type Type = String;
+
+struct Parameter {
+    name: Identifier,
+    typ: Type,
+}
+
+struct FuncDef {
+    name: Identifier,
+    parameters: Vec<Parameter>,
+    return_type: Option<Type>,
+    body: Box<Ast>,
+}
+
+#[derive(Debug)]
+struct AstError {
+    message: String,
+}
+
+impl AstError {
+    fn new(message: &str) -> Self {
+        AstError {
+            message: message.into(),
+        }
+    }
+}
+
+extern "C" {
+    fn tree_sitter_krone() -> Language;
+}
+
+struct TreeCursorChildrenIter<'a, A: AsRef<[u8]>> {
+    source: A,
+    cursor: &'a mut TreeCursor<'a>,
+    on_child: bool,
+}
+
+impl<'a, A: AsRef<[u8]>> Iterator for TreeCursorChildrenIter<'a, A> {
+    type Item = Result<Ast, AstError>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.on_child {
+            if self.cursor.goto_next_sibling() {
+                Some(parse_from_cursor(&self.source, self.cursor))
+            } else {
+                self.cursor.goto_parent();
+                None
+            }
+        } else {
+            if self.cursor.goto_first_child() {
+                self.on_child = true;
+                Some(parse_from_cursor(&self.source, self.cursor))
+            } else {
+                None
+            }
+        }
+    }
+}
+
+fn iter_children<'a, A: AsRef<[u8]>>(
+    source: A,
+    cursor: &'a mut TreeCursor<'a>,
+) -> TreeCursorChildrenIter<'a, A> {
+    TreeCursorChildrenIter {
+        source,
+        cursor,
+        on_child: false,
+    }
+}
+
+fn parse_from_cursor<'a>(
+    source: impl AsRef<[u8]>,
+    cursor: &'a mut TreeCursor<'a>,
+) -> Result<Ast, AstError> {
+    match cursor.node().kind() {
+        "block" => {
+            let mut statements = Vec::new();
+            let mut value = None;
+
+            for child in iter_children(source, cursor) {
+                match child.unwrap() {
+                    Ast::Statement(statement) => {
+                        if value.is_none() {
+                            statements.push(statement);
+                        } else {
+                            return Err(AstError::new(
+                                "cannot have a statement after an expression in a block",
+                            ));
+                            // perhaps there is a missing semicolon ;
+                        }
+                    }
+                    Ast::Expr(expr) => value = Some(expr),
+                    _ => return Err(AstError::new("invalid node type")),
+                };
+            }
+
+            let block = Ast::Block(statements, value);
+            Ok(block)
+        }
+
+        "function_definition" => {
+            // 1: name
+            assert!(cursor.goto_first_child());
+            assert!(cursor.field_name() == Some("name"));
+            let name: String = cursor
+                .node()
+                .utf8_text(source.as_ref())
+                .expect("utf8 error")
+                .into();
+
+            // 2: parameters
+            assert!(cursor.goto_next_sibling());
+            assert!(cursor.field_name() == Some("parameters"));
+            let mut parameters = Vec::new();
+
+            if cursor.goto_first_child() {
+                loop {
+                    let param = cursor.node();
+
+                    assert!(cursor.goto_first_child());
+                    let name = cursor
+                        .node()
+                        .utf8_text(source.as_ref())
+                        .expect("utf8 error")
+                        .into();
+
+                    assert!(cursor.goto_next_sibling());
+                    let typ = cursor
+                        .node()
+                        .utf8_text(source.as_ref())
+                        .expect("utf8 error")
+                        .into();
+
+                    cursor.goto_parent();
+
+                    parameters.push(Parameter { name, typ });
+
+                    if !cursor.goto_next_sibling() {
+                        break;
+                    }
+                }
+
+                cursor.goto_parent();
+            }
+
+            // 3: return type
+            assert!(cursor.goto_next_sibling());
+            assert!(cursor.field_name() == Some("return_type"));
+            let return_type = Some(
+                cursor
+                    .node()
+                    .utf8_text(source.as_ref())
+                    .expect("utf8 error")
+                    .into(),
+            );
+
+            // 4: body
+            assert!(cursor.goto_next_sibling());
+            assert!(cursor.field_name() == Some("body"));
+            let body = parse_from_cursor(source, cursor).unwrap();
+            let body = Box::new(body);
+
+            Ok(Ast::FuncDef(FuncDef {
+                name,
+                parameters,
+                return_type,
+                body,
+            }))
+        }
+
+        _ => panic!("unexpected node kind: {}", cursor.node().kind()),
+    }
+}
+
+fn parse_with_tree_sitter(source: impl AsRef<[u8]>) -> Result<Ast, AstError> {
+    let mut parser = Parser::new();
+    let language = unsafe { tree_sitter_krone() };
+    parser.set_language(language).unwrap();
+
+    let tree = parser.parse(&source, None).unwrap();
+
+    let mut cursor = tree.walk();
+    let node = cursor.node();
+    assert!(node.kind() == "source_file");
+    let mut top_level_nodes = Vec::new();
+
+    for node in iter_children(source, &mut cursor) {
+        let node = node.unwrap();
+        match node {
+            Ast::FuncDef(_) => top_level_nodes.push(node),
+            _ => panic!("unexpected top-level node type"),
+        };
+    }
+
+    Ok(Ast::Module(top_level_nodes))
+}

src/parsing/grammar.pest

@@ -1,52 +0,0 @@
-// This file is just a little test of pest.rs
-
-source_file = { SOI ~ definition* ~ EOI }
-
-statement        = { assign_statement | return_statement | call_statement }
-assign_statement = { "set" ~ ident ~ "=" ~ expr ~ ";" }
-return_statement = { "return" ~ expr? ~ ";" }
-call_statement   = { call ~ ";" }
-
-// Function calls
-call = { ident ~ "(" ~ args ~ ")" }
-args = { (expr ~ ",")* ~ expr? }
-
-definition = { func_def }
-
-func_def   = { "fn" ~ ident ~ "(" ~ parameters ~ ")" ~ typ? ~ block }
-parameters = {
-    (parameter ~ ",")* ~ (parameter)?
-}
-parameter  = { ident ~ ":" ~ typ }
-
-block = { "{" ~ statement* ~ expr? ~ "}" }
-
-// Operators
-infix    = _{ add | subtract | multiply | divide }
-add      =  { "+" }
-subtract =  { "-" }
-multiply =  { "*" }
-divide   =  { "/" }
-
-prefix = _{ not }
-not    =  { "!" }
-
-expr =  { prefix? ~ atom ~ (infix ~ prefix? ~ atom)* }
-atom = _{ call | ident | literal | "(" ~ expr ~ ")" }
-
-ident = @{ (ASCII_ALPHA | "_")+ }
-typ   = _{ ident }
-
-// Literals
-literal         = _{ float_literal | integer_literal | string_literal }
-string_literal  = ${ "\"" ~ string_content ~ "\"" }
-string_content  = @{ char* }
-char            =  {
-    !("\"" | "\\") ~ ANY
-  | "\\" ~ ("\"" | "\\" | "/" | "b" | "f" | "n" | "r" | "t")
-  | "\\" ~ ("u" ~ ASCII_HEX_DIGIT{4})
-}
-integer_literal = @{ ASCII_DIGIT+ }
-float_literal   = @{ ("0" | ASCII_NONZERO_DIGIT ~ ASCII_DIGIT*) ~ "." ~ ASCII_DIGIT* }
-
-WHITESPACE = _{ " " | "\n" | "\t" }

src/parsing/mod.rs

@@ -1,38 +1,5 @@
-pub mod pest;
+mod backend;
 
-pub use self::pest::parse;
+pub use self::backend::pest::{parse_file, parse_module};
 
-mod tests {
-    #[test]
-    fn test_addition_function() {
-        use crate::ast::*;
-        use crate::parsing::pest::parse;
-
-        let source = "fn add(a: int, b: int) int { a + b }";
-
-        let ast = Ast::FunctionDefinition(FunctionDefinition {
-            name: Identifier::from("add"),
-            parameters: vec![
-                Parameter {
-                    name: Identifier::from("a"),
-                    typ: Type::Int,
-                },
-                Parameter {
-                    name: Identifier::from("b"),
-                    typ: Type::Int,
-                },
-            ],
-            return_type: Some(Type::Int),
-            body: Box::new(Block {
-                statements: vec![],
-                value: Some(Expr::BinaryExpression(
-                    Box::new(Expr::Identifier(Identifier::from("a"))),
-                    BinaryOperator::Add,
-                    Box::new(Expr::Identifier(Identifier::from("b"))),
-                )),
-            }),
-        });
-
-        assert_eq!(parse(source).unwrap(), Ast::Module(vec![ast]));
-    }
-}
+mod tests;

src/parsing/tests.rs

@@ -0,0 +1,44 @@
+#[test]
+fn test_addition_function() {
+    use crate::parsing::backend::pest::parse_as_module;
+    use crate::{
+        ast::module::{Module, ModulePath},
+        ast::*,
+        typing::Type,
+    };
+
+    let source = "fn add(a: int, b: int) int { a + b }";
+    let path = ModulePath::from("test");
+    let module = parse_as_module(&source, path.clone()).expect("parsing error");
+
+    let expected_module = Module {
+        file: None,
+        imports: vec![],
+        definitions: vec![Definition::FunctionDefinition(FunctionDefinition {
+            name: Identifier::from("add"),
+            parameters: vec![
+                Parameter {
+                    name: Identifier::from("a"),
+                    typ: Type::Int,
+                },
+                Parameter {
+                    name: Identifier::from("b"),
+                    typ: Type::Int,
+                },
+            ],
+            return_type: Some(Type::Int),
+            body: Box::new(Block {
+                statements: vec![],
+                value: Some(Expr::BinaryExpression(
+                    Box::new(Expr::Identifier(Identifier::from("a"))),
+                    BinaryOperator::Add,
+                    Box::new(Expr::Identifier(Identifier::from("b"))),
+                )),
+            }),
+            line_col: (1, 1),
+        })],
+        path,
+    };
+
+    assert_eq!(module, expected_module);
+}

src/typing/mod.rs

@@ -0,0 +1,452 @@
+use std::collections::HashMap;
+
+use crate::ast::{
+    module::{Module, ModulePath},
+    *,
+};
+
+#[derive(Debug, PartialEq, Clone)]
+pub enum Type {
+    Bool,
+    Int,
+    Float,
+    Unit,
+    Str,
+    Custom(Identifier),
+}
+
+impl From<&str> for Type {
+    fn from(value: &str) -> Self {
+        match value {
+            "int" => Type::Int,
+            "float" => Type::Float,
+            _ => Type::Custom(Identifier::from(value)),
+        }
+    }
+}
+
+impl FunctionDefinition {
+    fn signature(&self) -> (Vec<Type>, Type) {
+        let return_type = self.return_type.unwrap_or(Type::Unit);
+        let params_types = self.parameters.iter().map(|p| p.typ).collect();
+        (params_types, return_type)
+    }
+}
+
+impl Module {
+    pub fn type_check(&self) -> Result<(), TypeError> {
+        let mut ctx = TypeContext::new(self.path);
+        ctx.file = self.file.clone();
+
+        // Register all function signatures
+        for Definition::FunctionDefinition(func) in &self.definitions {
+            if let Some(previous) = ctx.functions.insert(func.name.clone(), func.signature()) {
+                todo!("handle redefinition of function or identical function names across different files");
+            }
+        }
+
+        // TODO: add signatures of imported functions (even if they have not been checked)
+
+        // Type-check the function bodies
+        for Definition::FunctionDefinition(func) in &self.definitions {
+            func.typ(&mut ctx)?;
+        }
+
+        Ok(())
+    }
+}
+
+#[derive(Debug)]
+pub struct TypeError {
+    file: Option<std::path::PathBuf>,
+    module: ModulePath,
+    function: Option<String>,
+    kind: TypeErrorKind,
+}
+
+impl std::fmt::Display for TypeError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("Error\n")?;
+        if let Some(path) = &self.file {
+            f.write_fmt(format_args!(" in file {}\n", path.display()))?;
+        }
+        f.write_fmt(format_args!(" in module {}\n", self.module))?;
+        if let Some(name) = &self.function {
+            f.write_fmt(format_args!(" in function {}\n", name))?;
+        }
+        f.write_fmt(format_args!("{:#?}", self.kind))?;
+        Ok(())
+    }
+}
+
+#[derive(Default)]
+struct TypeErrorBuilder {
+    file: Option<std::path::PathBuf>,
+    module: Option<ModulePath>,
+    function: Option<String>,
+    kind: Option<TypeErrorKind>,
+}
+
+impl TypeError {
+    fn builder() -> TypeErrorBuilder {
+        TypeErrorBuilder::default()
+    }
+}
+
+impl TypeErrorBuilder {
+    fn context(mut self, ctx: &TypeContext) -> Self {
+        self.file = ctx.file.clone();
+        self.module = Some(ctx.module.clone());
+        self.function = ctx.function.clone();
+        self
+    }
+
+    fn kind(mut self, kind: TypeErrorKind) -> Self {
+        self.kind = Some(kind);
+        self
+    }
+
+    fn build(self) -> TypeError {
+        TypeError {
+            file: self.file,
+            module: self.module.expect("TypeError builder is missing module"),
+            function: self.function,
+            kind: self.kind.expect("TypeError builder is missing kind"),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub enum TypeErrorKind {
+    InvalidBinaryOperator {
+        operator: BinaryOperator,
+        lht: Type,
+        rht: Type,
+    },
+    BlockTypeDoesNotMatchFunctionType {
+        block_type: Type,
+        function_type: Type,
+    },
+    ReturnTypeDoesNotMatchFunctionType {
+        function_type: Type,
+        return_type: Type,
+    },
+    UnknownIdentifier {
+        identifier: String,
+    },
+    AssignmentMismatch {
+        lht: Type,
+        rht: Type,
+    },
+    AssignUndeclared,
+    VariableRedeclaration,
+    ReturnStatementsMismatch,
+    UnknownFunctionCalled(Identifier),
+    WrongFunctionArguments,
+    ConditionIsNotBool,
+    IfElseMismatch,
+}
+
+pub struct TypeContext {
+    pub file: Option<std::path::PathBuf>,
+    pub module: ModulePath,
+    pub function: Option<Identifier>,
+    pub functions: HashMap<Identifier, (Vec<Type>, Type)>,
+    pub variables: HashMap<Identifier, Type>,
+}
+
+impl TypeContext {
+    pub fn new(path: ModulePath) -> Self {
+        TypeContext {
+            file: None,
+            module: path,
+            function: None,
+            functions: Default::default(),
+            variables: Default::default(),
+        }
+    }
+}
+
+/// Trait for nodes which have a deducible type.
+pub trait Typ {
+    /// Try to resolve the type of the node.
+    fn typ(&self, ctx: &mut TypeContext) -> Result<Type, TypeError>;
+}
+
+impl Typ for FunctionDefinition {
+    fn typ(&self, ctx: &mut TypeContext) -> Result<Type, TypeError> {
+        let func = self;
+
+        ctx.function = Some(func.name.clone());
+
+        for param in &func.parameters {
+            ctx.variables.insert(param.name.clone(), param.typ.clone());
+        }
+
+        let body_type = &func.body.typ(ctx)?;
+
+        // If the return type is not specified, it is unit.
+        let func_return_type = match &func.return_type {
+            Some(typ) => typ,
+            None => &Type::Unit,
+        };
+
+        // Check coherence with the body's type.
+        if *func_return_type != *body_type {
+            return Err(TypeError::builder()
+                .context(ctx)
+                .kind(TypeErrorKind::BlockTypeDoesNotMatchFunctionType {
+                    block_type: body_type.clone(),
+                    function_type: func_return_type.clone(),
+                })
+                .build());
+        }
+
+        // Check coherence with return statements.
+        for statement in &func.body.statements {
+            if let Statement::ReturnStatement(value) = statement {
+                let ret_type = match value {
+                    Some(expr) => expr.typ(ctx)?,
+                    None => Type::Unit,
+                };
+                if ret_type != *func_return_type {
+                    return Err(TypeError::builder()
+                        .context(ctx)
+                        .kind(TypeErrorKind::ReturnTypeDoesNotMatchFunctionType {
+                            function_type: func_return_type.clone(),
+                            return_type: ret_type,
+                        })
+                        .build());
+                }
+            }
+        }
+
+        Ok(func_return_type.clone())
+    }
+}
+
+impl Typ for Block {
+    fn typ(&self, ctx: &mut TypeContext) -> Result<Type, TypeError> {
+        let mut return_typ: Option<Type> = None;
+
+        // Check declarations and assignments.
+        for statement in &self.statements {
+            match statement {
+                Statement::DeclareStatement(ident, expr) => {
+                    let typ = expr.typ(ctx)?;
+                    if let Some(_typ) = ctx.variables.insert(ident.clone(), typ) {
+                        // TODO: Shadowing? (illegal for now)
+                        return Err(TypeError::builder()
+                            .context(ctx)
+                            .kind(TypeErrorKind::VariableRedeclaration)
+                            .build());
+                    }
+                }
+                Statement::AssignStatement(ident, expr) => {
+                    let rhs_typ = expr.typ(ctx)?;
+                    let Some(lhs_typ) = ctx.variables.get(ident) else {
+                        return Err(TypeError::builder()
+                                   .context(ctx)
+                                   .kind(TypeErrorKind::AssignUndeclared)
+                                   .build());
+                    };
+
+                    // Ensure same type on both sides.
+                    if rhs_typ != *lhs_typ {
+                        return Err(TypeError::builder()
+                            .context(ctx)
+                            .kind(TypeErrorKind::AssignmentMismatch {
+                                lht: lhs_typ.clone(),
+                                rht: rhs_typ.clone(),
+                            })
+                            .build());
+                    }
+                }
+                Statement::ReturnStatement(maybe_expr) => {
+                    let expr_typ = if let Some(expr) = maybe_expr {
+                        expr.typ(ctx)?
+                    } else {
+                        Type::Unit
+                    };
+                    if let Some(typ) = &return_typ {
+                        if expr_typ != *typ {
+                            return Err(TypeError::builder()
+                                .context(ctx)
+                                .kind(TypeErrorKind::ReturnStatementsMismatch)
+                                .build());
+                        }
+                    } else {
+                        return_typ = Some(expr_typ);
+                    }
+                }
+                Statement::CallStatement(call) => {
+                    call.typ(ctx)?;
+                }
+                Statement::UseStatement(_path) => {
+                    // TODO: import the signatures (and types)
+                }
+                Statement::IfStatement(cond, block) => {
+                    if cond.typ(ctx)? != Type::Bool {
+                        return Err(TypeError::builder()
+                            .context(ctx)
+                            .kind(TypeErrorKind::ConditionIsNotBool)
+                            .build());
+                    }
+                    block.typ(ctx)?;
+                }
+                Statement::WhileStatement(cond, block) => {
+                    if cond.typ(ctx)? != Type::Bool {
+                        return Err(TypeError::builder()
+                            .context(ctx)
+                            .kind(TypeErrorKind::ConditionIsNotBool)
+                            .build());
+                    }
+                    block.typ(ctx)?;
+                }
+            }
+        }
+
+        // Check if there is an expression at the end of the block.
+        if let Some(expr) = &self.value {
+            expr.typ(ctx)
+        } else {
+            Ok(Type::Unit)
+        }
+
+        // TODO/FIXME: find a way to return `return_typ` so that the
+        // top-level block (the function) can check if this return type
+        // (and eventually those from other block) matches the type of
+        // the function.
+    }
+}
+
+impl Typ for Call {
+    fn typ(&self, ctx: &mut TypeContext) -> Result<Type, TypeError> {
+        match &self.callee {
+            Expr::Identifier(ident) => {
+                let signature = match ctx.functions.get(ident) {
+                    Some(sgn) => sgn.clone(),
+                    None => {
+                        return Err(TypeError::builder()
+                            .context(ctx)
+                            .kind(TypeErrorKind::UnknownFunctionCalled(ident.clone()))
+                            .build())
+                    }
+                };
+                let (params_types, func_type) = signature;
+
+                // Collect arg types.
+                let mut args_types: Vec<Type> = vec![];
+                for arg in &self.args {
+                    let typ = arg.typ(ctx)?;
+                    args_types.push(typ.clone());
+                }
+
+                if args_types == *params_types {
+                    Ok(func_type.clone())
+                } else {
+                    Err(TypeError::builder()
+                        .context(ctx)
+                        .kind(TypeErrorKind::WrongFunctionArguments)
+                        .build())
+                }
+            }
+            _ => unimplemented!("cannot call on expression other than identifier"),
+        }
+    }
+}
+
+impl Typ for Expr {
+    fn typ(&self, ctx: &mut TypeContext) -> Result<Type, TypeError> {
+        match self {
+            Expr::Identifier(identifier) => {
+                if let Some(typ) = ctx.variables.get(identifier) {
+                    Ok(typ.clone())
+                } else {
+                    Err(TypeError::builder()
+                        .context(ctx)
+                        .kind(TypeErrorKind::UnknownIdentifier {
+                            identifier: identifier.clone(),
+                        })
+                        .build())
+                }
+            }
+            Expr::BooleanLiteral(_) => Ok(Type::Bool),
+            Expr::IntegerLiteral(_) => Ok(Type::Int),
+            Expr::FloatLiteral(_) => Ok(Type::Float),
+            Expr::BinaryExpression(lhs, op, rhs) => match op {
+                BinaryOperator::Add
+                | BinaryOperator::Sub
+                | BinaryOperator::Mul
+                | BinaryOperator::Div => {
+                    let left_type = &lhs.typ(ctx)?;
+                    let right_type = &rhs.typ(ctx)?;
+                    match (left_type, right_type) {
+                        (Type::Int, Type::Int) => Ok(Type::Int),
+                        (Type::Float, Type::Float) => Ok(Type::Float),
+                        (_, _) => Err(TypeError::builder()
+                            .context(ctx)
+                            .kind(TypeErrorKind::InvalidBinaryOperator {
+                                operator: op.clone(),
+                                lht: left_type.clone(),
+                                rht: right_type.clone(),
+                            })
+                            .build()),
+                    }
+                }
+                BinaryOperator::Equal | BinaryOperator::NotEqual => {
+                    let lhs_type = lhs.typ(ctx)?;
+                    let rhs_type = rhs.typ(ctx)?;
+                    if lhs_type != rhs_type {
+                        return Err(TypeError::builder()
+                            .context(ctx)
+                            .kind(TypeErrorKind::InvalidBinaryOperator {
+                                operator: op.clone(),
+                                lht: lhs_type.clone(),
+                                rht: rhs_type.clone(),
+                            })
+                            .build());
+                    }
+                    Ok(Type::Bool)
+                }
+                BinaryOperator::Modulo => {
+                    let lhs_type = lhs.typ(ctx)?;
+                    let rhs_type = lhs.typ(ctx)?;
+                    match (&lhs_type, &rhs_type) {
+                        (Type::Int, Type::Int) => Ok(Type::Int),
+                        _ => Err(TypeError::builder()
+                            .context(ctx)
+                            .kind(TypeErrorKind::InvalidBinaryOperator {
+                                operator: op.clone(),
+                                lht: lhs_type.clone(),
+                                rht: rhs_type.clone(),
+                            })
+                            .build()),
+                    }
+                }
+            },
+            Expr::StringLiteral(_) => Ok(Type::Str),
+            Expr::Call(call) => call.typ(ctx),
+            Expr::Block(block) => block.typ(ctx),
+            Expr::IfExpr(cond, true_block, else_value) => {
+                if cond.typ(ctx)? != Type::Bool {
+                    Err(TypeError::builder()
+                        .context(ctx)
+                        .kind(TypeErrorKind::ConditionIsNotBool)
+                        .build())
+                } else {
+                    let true_block_type = true_block.typ(ctx)?;
+                    let else_type = else_value.typ(ctx)?;
+                    if true_block_type != else_type {
+                        Err(TypeError::builder()
+                            .context(ctx)
+                            .kind(TypeErrorKind::IfElseMismatch)
+                            .build())
+                    } else {
+                        Ok(true_block_type.clone())
+                    }
+                }
+            }
+        }
+    }
+}