diff --git a/fluxc/src/ast.rs b/fluxc/src/ast.rs
index d5a7f7a..782f877 100644
--- a/fluxc/src/ast.rs
+++ b/fluxc/src/ast.rs
@@ -201,3 +201,64 @@ pub enum StmtKind {
     /// Error placeholder — emitted during recovery so the parent can continue.
     Error,
 }
+
+// ── Top-level definitions ──────────────────────────────────────────────────────
+
+/// A function parameter: `[mut] name : type`.
+#[derive(Debug, Clone)]
+pub struct Param {
+    pub mutable: bool,
+    pub name: String,
+    pub name_span: Span,
+    pub ty: Type,
+}
+
+/// A struct definition field: `name : type`.
+///
+/// Named `FieldDef` to distinguish from `StructField`, which is a
+/// field in a struct *literal expression*.
+#[derive(Debug, Clone)]
+pub struct FieldDef {
+    pub name: String,
+    pub name_span: Span,
+    pub ty: Type,
+}
+
+/// `fn name ( params ) [ -> type ] block`
+#[derive(Debug, Clone)]
+pub struct FuncDef {
+    pub name: String,
+    pub name_span: Span,
+    pub params: Vec<Param>,
+    pub ret_ty: Option<Type>,
+    pub body: Block,
+}
+
+/// `struct name { fields }`
+#[derive(Debug, Clone)]
+pub struct StructDef {
+    pub name: String,
+    pub name_span: Span,
+    pub fields: Vec<FieldDef>,
+}
+
+#[derive(Debug, Clone)]
+pub struct TopLevelDef {
+    pub kind: TopLevelDefKind,
+    pub span: Span,
+}
+
+#[derive(Debug, Clone)]
+pub enum TopLevelDefKind {
+    Func(FuncDef),
+    Struct(StructDef),
+    /// Error placeholder for recovery.
+    Error,
+}
+
+/// The root of the AST — a sequence of top-level definitions.
+#[derive(Debug, Clone)]
+pub struct Program {
+    pub defs: Vec<TopLevelDef>,
+    pub span: Span,
+}
diff --git a/fluxc/src/main.rs b/fluxc/src/main.rs
index cae111d..10cd541 100644
--- a/fluxc/src/main.rs
+++ b/fluxc/src/main.rs
@@ -1,4 +1,4 @@
-use std::io::{self, BufRead, Write};
+use std::{env::args, fs};
 
 use crate::parser::Parser;
 
@@ -8,39 +8,18 @@ pub mod parser;
 pub mod token;
 
 fn main() {
-    let stdin = io::stdin();
-    let stdout = io::stdout();
+    let path = args().nth(1).expect("usage: fluxc <file>");
+    let content = fs::read_to_string(&path).unwrap_or_else(|e| {
+        eprintln!("error: {e}");
+        std::process::exit(1)
+    });
 
-    println!("flux expression REPL (ctrl+d to exit)");
+    let mut parser = Parser::new(&content);
+    let program = parser.parse_program();
 
-    loop {
-        print!("> ");
-        stdout.lock().flush().unwrap();
-
-        let mut line = String::new();
-        match stdin.lock().read_line(&mut line) {
-            Ok(0) => break, // EOF
-            Ok(_) => {}
-            Err(e) => {
-                eprintln!("error: {e}");
-                break;
-            }
-        }
-
-        let src = line.trim();
-        if src.is_empty() {
-            continue;
-        }
-
-        let mut parser = Parser::new(src);
-        let node = parser.parse_stmt();
-
-        for err in &parser.errors {
-            eprintln!("parse error: {err}");
-        }
-
-        if parser.errors.is_empty() {
-            println!("{node:#?}");
-        }
+    for err in &parser.errors {
+        eprintln!("parse error: {err}");
     }
+
+    println!("{program:#?}");
 }
diff --git a/fluxc/src/parser.rs b/fluxc/src/parser.rs
index 5de1f44..ec91dc7 100644
--- a/fluxc/src/parser.rs
+++ b/fluxc/src/parser.rs
@@ -2,7 +2,8 @@ use std::fmt;
 
 use crate::{
     ast::{
-        BinaryOp, Block, ElseBranch, Expr, ExprKind, Stmt, StmtKind, StructField, Type, UnaryOp,
+        BinaryOp, Block, ElseBranch, Expr, ExprKind, FieldDef, FuncDef, Param, Program, Stmt,
+        StmtKind, StructDef, StructField, TopLevelDef, TopLevelDefKind, Type, UnaryOp,
     },
     lexer::Lexer,
     token::{Span, Token, TokenKind},
@@ -657,6 +658,158 @@ impl<'src> Parser<'src> {
 
     // ── Argument list ─────────────────────────────────────────────────────────
 
+    // ── Top-level definitions ─────────────────────────────────────────────────
+
+    /// Parse an entire source file as a `Program`.
+    pub fn parse_program(&mut self) -> Program {
+        let start = self.current().span;
+        let mut defs = Vec::new();
+        loop {
+            if self.current().kind == TokenKind::Eof {
+                break;
+            }
+            defs.push(self.parse_top_level_def());
+        }
+        let span = start.cover(self.current().span);
+        Program { defs, span }
+    }
+
+    /// Parse one top-level definition (`fn` or `struct`).
+    pub fn parse_top_level_def(&mut self) -> TopLevelDef {
+        let tok = self.current();
+        match tok.kind {
+            TokenKind::Fn => self.parse_func_def(),
+            TokenKind::Struct => self.parse_struct_def(),
+            _ => {
+                self.errors.push(ParseError {
+                    span: tok.span,
+                    message: format!("expected `fn` or `struct`, found {}", tok.kind),
+                });
+                self.synchronize_top_level();
+                TopLevelDef {
+                    kind: TopLevelDefKind::Error,
+                    span: tok.span,
+                }
+            }
+        }
+    }
+
+    /// Skip tokens until the next top-level boundary (`fn`, `struct`, or EOF).
+    fn synchronize_top_level(&mut self) {
+        loop {
+            match self.current().kind {
+                TokenKind::Eof | TokenKind::Fn | TokenKind::Struct => break,
+                _ => {
+                    self.advance();
+                }
+            }
+        }
+    }
+
+    fn parse_func_def(&mut self) -> TopLevelDef {
+        let kw = self.advance(); // consume `fn`
+        let name_tok = self.expect(TokenKind::Ident);
+        self.expect(TokenKind::LParen);
+        let params = self.parse_param_list();
+        self.expect(TokenKind::RParen);
+        let ret_ty = if self.current().kind == TokenKind::Arrow {
+            self.advance();
+            Some(self.parse_type())
+        } else {
+            None
+        };
+        let body = self.parse_block();
+        let span = kw.span.cover(body.span);
+        TopLevelDef {
+            kind: TopLevelDefKind::Func(FuncDef {
+                name: name_tok.text.to_owned(),
+                name_span: name_tok.span,
+                params,
+                ret_ty,
+                body,
+            }),
+            span,
+        }
+    }
+
+    fn parse_param_list(&mut self) -> Vec<Param> {
+        let mut params = Vec::new();
+        loop {
+            if matches!(self.current().kind, TokenKind::RParen | TokenKind::Eof) {
+                break;
+            }
+            params.push(self.parse_param());
+            if self.current().kind == TokenKind::Comma {
+                self.advance();
+            } else {
+                break;
+            }
+        }
+        params
+    }
+
+    fn parse_param(&mut self) -> Param {
+        let mutable = if self.current().kind == TokenKind::Mut {
+            self.advance();
+            true
+        } else {
+            false
+        };
+        let name_tok = self.expect(TokenKind::Ident);
+        self.expect(TokenKind::Colon);
+        let ty = self.parse_type();
+        Param {
+            mutable,
+            name: name_tok.text.to_owned(),
+            name_span: name_tok.span,
+            ty,
+        }
+    }
+
+    fn parse_struct_def(&mut self) -> TopLevelDef {
+        let kw = self.advance(); // consume `struct`
+        let name_tok = self.expect(TokenKind::Ident);
+        self.expect(TokenKind::LCurly);
+        let fields = self.parse_field_def_list();
+        let close = self.expect(TokenKind::RCurly);
+        let span = kw.span.cover(close.span);
+        TopLevelDef {
+            kind: TopLevelDefKind::Struct(StructDef {
+                name: name_tok.text.to_owned(),
+                name_span: name_tok.span,
+                fields,
+            }),
+            span,
+        }
+    }
+
+    fn parse_field_def_list(&mut self) -> Vec<FieldDef> {
+        let mut fields = Vec::new();
+        loop {
+            if matches!(self.current().kind, TokenKind::RCurly | TokenKind::Eof) {
+                break;
+            }
+            fields.push(self.parse_field_def());
+            if self.current().kind == TokenKind::Comma {
+                self.advance();
+            } else {
+                break;
+            }
+        }
+        fields
+    }
+
+    fn parse_field_def(&mut self) -> FieldDef {
+        let name_tok = self.expect(TokenKind::Ident);
+        self.expect(TokenKind::Colon);
+        let ty = self.parse_type();
+        FieldDef {
+            name: name_tok.text.to_owned(),
+            name_span: name_tok.span,
+            ty,
+        }
+    }
+
     /// Parse `arg, arg, …` up to `)`. The opening `(` has already been
     /// consumed by `parse_led`. Returns `(args, close_span)`.
     fn parse_arg_list(&mut self) -> (Vec<Expr>, Span) {
@@ -683,7 +836,7 @@ impl<'src> Parser<'src> {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::ast::{ElseBranch, ExprKind, StmtKind, Type};
+    use crate::ast::{ElseBranch, ExprKind, StmtKind, TopLevelDefKind, Type};
 
     // ── Expression test helpers ───────────────────────────────────────────────
 
@@ -1165,4 +1318,169 @@ mod tests {
         let s = p.parse_stmt();
         assert!(matches!(s.kind, StmtKind::If { .. }));
     }
+
+    // ── Function definition tests ─────────────────────────────────────────────
+
+    fn top(src: &str) -> TopLevelDef {
+        Parser::new(src).parse_top_level_def()
+    }
+
+    #[test]
+    fn func_def_empty() {
+        let d = top("fn foo() { }");
+        match &d.kind {
+            TopLevelDefKind::Func(f) => {
+                assert_eq!(f.name, "foo");
+                assert!(f.params.is_empty());
+                assert!(f.ret_ty.is_none());
+            }
+            _ => panic!("expected func def"),
+        }
+    }
+
+    #[test]
+    fn func_def_with_return_type() {
+        let d = top("fn answer() -> i32 { return 42; }");
+        match &d.kind {
+            TopLevelDefKind::Func(f) => {
+                assert!(matches!(f.ret_ty, Some(Type::I32)));
+            }
+            _ => panic!("expected func def"),
+        }
+    }
+
+    #[test]
+    fn func_def_params() {
+        let d = top("fn add(a: i32, b: i32) -> i32 { return a + b; }");
+        match &d.kind {
+            TopLevelDefKind::Func(f) => {
+                assert_eq!(f.params.len(), 2);
+                assert_eq!(f.params[0].name, "a");
+                assert!(!f.params[0].mutable);
+                assert!(matches!(f.params[0].ty, Type::I32));
+                assert_eq!(f.params[1].name, "b");
+            }
+            _ => panic!("expected func def"),
+        }
+    }
+
+    #[test]
+    fn func_def_mut_param() {
+        let d = top("fn inc(mut n: i32) -> i32 { n = n + 1; return n; }");
+        match &d.kind {
+            TopLevelDefKind::Func(f) => {
+                assert!(f.params[0].mutable);
+            }
+            _ => panic!("expected func def"),
+        }
+    }
+
+    #[test]
+    fn func_def_pointer_param() {
+        let d = top("fn foo(p: *i32) { }");
+        match &d.kind {
+            TopLevelDefKind::Func(f) => {
+                assert!(matches!(f.params[0].ty, Type::Pointer(_)));
+            }
+            _ => panic!("expected func def"),
+        }
+    }
+
+    // ── Struct definition tests ───────────────────────────────────────────────
+
+    #[test]
+    fn struct_def_empty() {
+        let d = top("struct Empty { }");
+        match &d.kind {
+            TopLevelDefKind::Struct(s) => {
+                assert_eq!(s.name, "Empty");
+                assert!(s.fields.is_empty());
+            }
+            _ => panic!("expected struct def"),
+        }
+    }
+
+    #[test]
+    fn struct_def_with_fields() {
+        let d = top("struct Point { x: f64, y: f64 }");
+        match &d.kind {
+            TopLevelDefKind::Struct(s) => {
+                assert_eq!(s.name, "Point");
+                assert_eq!(s.fields.len(), 2);
+                assert_eq!(s.fields[0].name, "x");
+                assert!(matches!(s.fields[0].ty, Type::F64));
+                assert_eq!(s.fields[1].name, "y");
+            }
+            _ => panic!("expected struct def"),
+        }
+    }
+
+    #[test]
+    fn struct_def_named_field_type() {
+        let d = top("struct Node { value: i32, next: *Node }");
+        match &d.kind {
+            TopLevelDefKind::Struct(s) => {
+                assert!(matches!(s.fields[1].ty, Type::Pointer(_)));
+            }
+            _ => panic!("expected struct def"),
+        }
+    }
+
+    // ── Program tests ─────────────────────────────────────────────────────────
+
+    fn program(src: &str) -> Program {
+        Parser::new(src).parse_program()
+    }
+
+    #[test]
+    fn program_empty() {
+        let p = program("");
+        assert!(p.defs.is_empty());
+    }
+
+    #[test]
+    fn program_single_func() {
+        let p = program("fn main() { }");
+        assert_eq!(p.defs.len(), 1);
+        assert!(matches!(p.defs[0].kind, TopLevelDefKind::Func(_)));
+    }
+
+    #[test]
+    fn program_struct_and_func() {
+        let src = "struct Point { x: f64, y: f64 }  fn main() { }";
+        let p = program(src);
+        assert_eq!(p.defs.len(), 2);
+        assert!(matches!(p.defs[0].kind, TopLevelDefKind::Struct(_)));
+        assert!(matches!(p.defs[1].kind, TopLevelDefKind::Func(_)));
+    }
+
+    #[test]
+    fn program_multiple_funcs() {
+        let src = "fn foo() { } fn bar() -> i32 { return 1; } fn baz(x: bool) { }";
+        let p = program(src);
+        assert_eq!(p.defs.len(), 3);
+    }
+
+    // ── Top-level recovery tests ──────────────────────────────────────────────
+
+    #[test]
+    fn top_level_stray_token_synchronizes() {
+        // A stray token should produce Error and then the next definition
+        // should still parse correctly.
+        let mut p = Parser::new("42 fn foo() { }");
+        let d1 = p.parse_top_level_def();
+        let d2 = p.parse_top_level_def();
+        assert!(matches!(d1.kind, TopLevelDefKind::Error));
+        assert!(matches!(d2.kind, TopLevelDefKind::Func(_)));
+        assert!(!p.errors.is_empty());
+    }
+
+    #[test]
+    fn top_level_missing_func_name_inserts_dummy() {
+        // `fn () { }` — missing name; expect() inserts a dummy, no panic.
+        let mut p = Parser::new("fn () { }");
+        let d = p.parse_top_level_def();
+        assert!(!p.errors.is_empty());
+        assert!(matches!(d.kind, TopLevelDefKind::Func(_)));
+    }
 }