commit a40058a5b5365b5e05a32eb8ba8ef34d2d3b51ab
from: Murilo Ijanc <murilo.ijanc@kovi.com.br>
date: Fri Nov 14 18:00:00 2025 UTC

Add full parser with statements and functions

Parse complete programs: FnDecl, let/let mut,
if/else/else if, while, for..in range(), return,
print, assignments. Semicolons terminate statements,
last expression without semicolon is implicit return.

commit - ebe3a0a72c98c733977195ad2a30c57189ce8701
commit + a40058a5b5365b5e05a32eb8ba8ef34d2d3b51ab
blob - 8aaab798979dedf14befb4da4574d361936120d1
blob + 0e3ae3e1108786e6afd353e596e2f0870e775006
--- src/main.rs
+++ src/main.rs
@@ -67,8 +67,8 @@ fn cmd_parse(source: &str) {
     };
 
     let mut parser = parser::Parser::new(tokens);
-    match parser.parse_expression() {
-        Ok(expr) => println!("{:#?}", expr),
+    match parser.parse_program() {
+        Ok(program) => println!("{:#?}", program),
         Err(e) => {
             eprintln!("{e}");
             process::exit(1);
blob - 1445329a8518ba61dfc298e9e4c639e637afe502
blob + a88808288eaec57a056546e818e1e2810e707b67
--- src/parser/ast.rs
+++ src/parser/ast.rs
@@ -18,6 +18,82 @@
 use crate::span::Span;
 
 #[derive(Debug, Clone)]
+pub enum Type {
+    Int,
+    Float,
+    Str,
+    Bool,
+}
+
+#[derive(Debug, Clone)]
+pub struct Param {
+    pub name: String,
+    pub ty: Type,
+    pub span: Span,
+}
+
+#[derive(Debug, Clone)]
+pub struct FnDecl {
+    pub name: String,
+    pub params: Vec<Param>,
+    pub return_ty: Option<Type>,
+    pub body: Block,
+    pub span: Span,
+}
+
+#[derive(Debug, Clone)]
+pub struct Program {
+    pub functions: Vec<FnDecl>,
+}
+
+pub type Block = Vec<Stmt>;
+
+#[derive(Debug, Clone)]
+pub enum Stmt {
+    Let {
+        name: String,
+        mutable: bool,
+        ty: Option<Type>,
+        value: Expr,
+        span: Span,
+    },
+    Assign {
+        name: String,
+        value: Expr,
+        span: Span,
+    },
+    If {
+        condition: Expr,
+        then_block: Block,
+        else_block: Option<Block>,
+        span: Span,
+    },
+    For {
+        var: String,
+        iter: Expr,
+        body: Block,
+        span: Span,
+    },
+    While {
+        condition: Expr,
+        body: Block,
+        span: Span,
+    },
+    Return {
+        value: Option<Expr>,
+        span: Span,
+    },
+    Print {
+        args: Vec<Expr>,
+        span: Span,
+    },
+    ExprStmt {
+        expr: Expr,
+        span: Span,
+    },
+}
+
+#[derive(Debug, Clone)]
 pub enum BinOp {
     Add,
     Sub,
blob - fefc755e3dac17e7b89ce7583e1752d34287c4b7
blob + 4d736731fc3365f00b0fa9ef325be1462bb09896
--- src/parser/mod.rs
+++ src/parser/mod.rs
@@ -20,7 +20,10 @@ pub mod ast;
 use crate::error::OlangError;
 use crate::lexer::token::{Token, TokenKind};
 use crate::span::Span;
-use ast::{BinOp, Expr, UnaryOp};
+use ast::{
+    BinOp, Block, Expr, FnDecl, Param, Program, Stmt,
+    Type, UnaryOp,
+};
 
 pub struct Parser {
     tokens: Vec<Token>,
@@ -66,6 +69,355 @@ impl Parser {
         }
     }
 
+    fn expect_ident(
+        &mut self,
+    ) -> Result<(String, Span), OlangError> {
+        let token = self.advance().clone();
+        if let TokenKind::Ident(name) = token.kind {
+            Ok((name, token.span))
+        } else {
+            Err(OlangError::new(
+                format!(
+                    "expected identifier, found {:?}",
+                    token.kind
+                ),
+                token.span,
+            ))
+        }
+    }
+
+    // --- Program ---
+
+    pub fn parse_program(
+        &mut self,
+    ) -> Result<Program, OlangError> {
+        let mut functions = Vec::new();
+
+        while *self.peek() != TokenKind::Eof {
+            functions.push(self.parse_fn_decl()?);
+        }
+
+        Ok(Program { functions })
+    }
+
+    fn parse_fn_decl(
+        &mut self,
+    ) -> Result<FnDecl, OlangError> {
+        let start = self.expect(&TokenKind::Fn)?;
+        let (name, _) = self.expect_ident()?;
+
+        self.expect(&TokenKind::LParen)?;
+        let params = self.parse_params()?;
+        self.expect(&TokenKind::RParen)?;
+
+        let return_ty = if *self.peek() == TokenKind::Arrow
+        {
+            self.advance();
+            Some(self.parse_type()?)
+        } else {
+            None
+        };
+
+        let body = self.parse_block()?;
+        let end = self.tokens[self.pos - 1].span;
+
+        Ok(FnDecl {
+            name,
+            params,
+            return_ty,
+            body,
+            span: Span::new(start.start, end.end),
+        })
+    }
+
+    fn parse_params(
+        &mut self,
+    ) -> Result<Vec<Param>, OlangError> {
+        let mut params = Vec::new();
+
+        if *self.peek() == TokenKind::RParen {
+            return Ok(params);
+        }
+
+        params.push(self.parse_param()?);
+        while *self.peek() == TokenKind::Comma {
+            self.advance();
+            params.push(self.parse_param()?);
+        }
+
+        Ok(params)
+    }
+
+    fn parse_param(
+        &mut self,
+    ) -> Result<Param, OlangError> {
+        let (name, start) = self.expect_ident()?;
+        self.expect(&TokenKind::Colon)?;
+        let ty = self.parse_type()?;
+        let end = self.tokens[self.pos - 1].span;
+
+        Ok(Param {
+            name,
+            ty,
+            span: Span::new(start.start, end.end),
+        })
+    }
+
+    fn parse_type(
+        &mut self,
+    ) -> Result<Type, OlangError> {
+        let token = self.advance().clone();
+        match token.kind {
+            TokenKind::IntType => Ok(Type::Int),
+            TokenKind::FloatType => Ok(Type::Float),
+            TokenKind::StrType => Ok(Type::Str),
+            TokenKind::BoolType => Ok(Type::Bool),
+            _ => Err(OlangError::new(
+                format!(
+                    "expected type, found {:?}",
+                    token.kind
+                ),
+                token.span,
+            )),
+        }
+    }
+
+    // --- Block ---
+
+    fn parse_block(
+        &mut self,
+    ) -> Result<Block, OlangError> {
+        self.expect(&TokenKind::LBrace)?;
+        let mut stmts = Vec::new();
+
+        while *self.peek() != TokenKind::RBrace {
+            stmts.push(self.parse_statement()?);
+        }
+
+        self.expect(&TokenKind::RBrace)?;
+        Ok(stmts)
+    }
+
+    // --- Statements ---
+
+    fn parse_statement(
+        &mut self,
+    ) -> Result<Stmt, OlangError> {
+        match self.peek() {
+            TokenKind::Let => self.parse_let(),
+            TokenKind::If => self.parse_if(),
+            TokenKind::For => self.parse_for(),
+            TokenKind::While => self.parse_while(),
+            TokenKind::Return => self.parse_return(),
+            TokenKind::Print => self.parse_print(),
+            _ => self.parse_assign_or_expr(),
+        }
+    }
+
+    fn parse_let(
+        &mut self,
+    ) -> Result<Stmt, OlangError> {
+        let start = self.expect(&TokenKind::Let)?;
+
+        let mutable =
+            if *self.peek() == TokenKind::Mut {
+                self.advance();
+                true
+            } else {
+                false
+            };
+
+        let (name, _) = self.expect_ident()?;
+
+        let ty = if *self.peek() == TokenKind::Colon {
+            self.advance();
+            Some(self.parse_type()?)
+        } else {
+            None
+        };
+
+        self.expect(&TokenKind::Eq)?;
+        let value = self.parse_expression()?;
+        let end = self.expect(&TokenKind::Semicolon)?;
+
+        Ok(Stmt::Let {
+            name,
+            mutable,
+            ty,
+            value,
+            span: Span::new(start.start, end.end),
+        })
+    }
+
+    fn parse_if(
+        &mut self,
+    ) -> Result<Stmt, OlangError> {
+        let start = self.expect(&TokenKind::If)?;
+        let condition = self.parse_expression()?;
+        let then_block = self.parse_block()?;
+
+        let else_block =
+            if *self.peek() == TokenKind::Else {
+                self.advance();
+                if *self.peek() == TokenKind::If {
+                    // else if -> wrap in a block with
+                    // one If statement
+                    let if_stmt = self.parse_if()?;
+                    Some(vec![if_stmt])
+                } else {
+                    Some(self.parse_block()?)
+                }
+            } else {
+                None
+            };
+
+        let end = self.tokens[self.pos - 1].span;
+
+        Ok(Stmt::If {
+            condition,
+            then_block,
+            else_block,
+            span: Span::new(start.start, end.end),
+        })
+    }
+
+    fn parse_for(
+        &mut self,
+    ) -> Result<Stmt, OlangError> {
+        let start = self.expect(&TokenKind::For)?;
+        let (var, _) = self.expect_ident()?;
+        self.expect(&TokenKind::In)?;
+
+        // Parse range(expr)
+        let range_start = self.peek_span();
+        self.expect(&TokenKind::Range)?;
+        self.expect(&TokenKind::LParen)?;
+        let limit = self.parse_expression()?;
+        let range_end =
+            self.expect(&TokenKind::RParen)?;
+
+        let iter = Expr::Call {
+            name: "range".to_string(),
+            args: vec![limit],
+            span: Span::new(
+                range_start.start,
+                range_end.end,
+            ),
+        };
+
+        let body = self.parse_block()?;
+        let end = self.tokens[self.pos - 1].span;
+
+        Ok(Stmt::For {
+            var,
+            iter,
+            body,
+            span: Span::new(start.start, end.end),
+        })
+    }
+
+    fn parse_while(
+        &mut self,
+    ) -> Result<Stmt, OlangError> {
+        let start = self.expect(&TokenKind::While)?;
+        let condition = self.parse_expression()?;
+        let body = self.parse_block()?;
+        let end = self.tokens[self.pos - 1].span;
+
+        Ok(Stmt::While {
+            condition,
+            body,
+            span: Span::new(start.start, end.end),
+        })
+    }
+
+    fn parse_return(
+        &mut self,
+    ) -> Result<Stmt, OlangError> {
+        let start = self.expect(&TokenKind::Return)?;
+
+        let value =
+            if *self.peek() == TokenKind::Semicolon {
+                None
+            } else {
+                Some(self.parse_expression()?)
+            };
+
+        let end = self.expect(&TokenKind::Semicolon)?;
+
+        Ok(Stmt::Return {
+            value,
+            span: Span::new(start.start, end.end),
+        })
+    }
+
+    fn parse_print(
+        &mut self,
+    ) -> Result<Stmt, OlangError> {
+        let start = self.expect(&TokenKind::Print)?;
+        self.expect(&TokenKind::LParen)?;
+
+        let mut args = Vec::new();
+        if *self.peek() != TokenKind::RParen {
+            args.push(self.parse_expression()?);
+            while *self.peek() == TokenKind::Comma {
+                self.advance();
+                args.push(self.parse_expression()?);
+            }
+        }
+
+        self.expect(&TokenKind::RParen)?;
+        let end = self.expect(&TokenKind::Semicolon)?;
+
+        Ok(Stmt::Print {
+            args,
+            span: Span::new(start.start, end.end),
+        })
+    }
+
+    fn parse_assign_or_expr(
+        &mut self,
+    ) -> Result<Stmt, OlangError> {
+        let expr = self.parse_expression()?;
+
+        // Check if it's an assignment: ident = expr;
+        if let Expr::Ident(ref name, _) = expr {
+            if *self.peek() == TokenKind::Eq {
+                let name = name.clone();
+                let start = self.span_of(&expr);
+                self.advance();
+                let value = self.parse_expression()?;
+                let end =
+                    self.expect(&TokenKind::Semicolon)?;
+                return Ok(Stmt::Assign {
+                    name,
+                    value,
+                    span: Span::new(
+                        start.start,
+                        end.end,
+                    ),
+                });
+            }
+        }
+
+        let span = self.span_of(&expr);
+
+        // Expression statement with ;
+        if *self.peek() == TokenKind::Semicolon {
+            let end =
+                self.expect(&TokenKind::Semicolon)?;
+            return Ok(Stmt::ExprStmt {
+                expr,
+                span: Span::new(span.start, end.end),
+            });
+        }
+
+        // Expression without ; (implicit return)
+        Ok(Stmt::ExprStmt { expr, span })
+    }
+
+    // --- Expressions ---
+
     pub fn parse_expression(
         &mut self,
     ) -> Result<Expr, OlangError> {
@@ -76,6 +428,7 @@ impl Parser {
         &mut self,
     ) -> Result<Expr, OlangError> {
         let mut left = self.parse_comparison()?;
+
         loop {
             let op = match self.peek() {
                 TokenKind::EqEq => BinOp::Eq,
@@ -95,6 +448,7 @@ impl Parser {
                 span,
             };
         }
+
         Ok(left)
     }
 
@@ -102,14 +456,13 @@ impl Parser {
         &mut self,
     ) -> Result<Expr, OlangError> {
         let mut left = self.parse_addition()?;
+
         loop {
             let op = match self.peek() {
                 TokenKind::Less => BinOp::Less,
                 TokenKind::LessEq => BinOp::LessEq,
                 TokenKind::Greater => BinOp::Greater,
-                TokenKind::GreaterEq => {
-                    BinOp::GreaterEq
-                }
+                TokenKind::GreaterEq => BinOp::GreaterEq,
                 _ => break,
             };
             self.advance();
@@ -125,6 +478,7 @@ impl Parser {
                 span,
             };
         }
+
         Ok(left)
     }
 
@@ -132,6 +486,7 @@ impl Parser {
         &mut self,
     ) -> Result<Expr, OlangError> {
         let mut left = self.parse_multiply()?;
+
         loop {
             let op = match self.peek() {
                 TokenKind::Plus => BinOp::Add,
@@ -151,6 +506,7 @@ impl Parser {
                 span,
             };
         }
+
         Ok(left)
     }
 
@@ -158,6 +514,7 @@ impl Parser {
         &mut self,
     ) -> Result<Expr, OlangError> {
         let mut left = self.parse_unary()?;
+
         loop {
             let op = match self.peek() {
                 TokenKind::Star => BinOp::Mul,
@@ -178,6 +535,7 @@ impl Parser {
                 span,
             };
         }
+
         Ok(left)
     }
 
@@ -185,6 +543,7 @@ impl Parser {
         &mut self,
     ) -> Result<Expr, OlangError> {
         let start = self.peek_span();
+
         if *self.peek() == TokenKind::Minus {
             self.advance();
             let expr = self.parse_unary()?;
@@ -198,6 +557,7 @@ impl Parser {
                 span,
             });
         }
+
         self.parse_call()
     }
 
@@ -205,18 +565,17 @@ impl Parser {
         &mut self,
     ) -> Result<Expr, OlangError> {
         let expr = self.parse_primary()?;
+
         if let Expr::Ident(ref name, _) = expr {
             if *self.peek() == TokenKind::LParen {
                 let name = name.clone();
                 let start = self.span_of(&expr);
                 self.advance();
                 let mut args = Vec::new();
+
                 if *self.peek() != TokenKind::RParen {
-                    args.push(
-                        self.parse_expression()?,
-                    );
-                    while *self.peek()
-                        == TokenKind::Comma
+                    args.push(self.parse_expression()?);
+                    while *self.peek() == TokenKind::Comma
                     {
                         self.advance();
                         args.push(
@@ -224,6 +583,7 @@ impl Parser {
                         );
                     }
                 }
+
                 let end =
                     self.expect(&TokenKind::RParen)?;
                 let span =
@@ -235,6 +595,7 @@ impl Parser {
                 });
             }
         }
+
         Ok(expr)
     }
 
@@ -242,6 +603,7 @@ impl Parser {
         &mut self,
     ) -> Result<Expr, OlangError> {
         let token = self.advance().clone();
+
         match token.kind {
             TokenKind::IntLit(v) => {
                 Ok(Expr::IntLit(v, token.span))