diff --git a/src/libctonfile/parser.rs b/src/libctonfile/parser.rs
index 44cf3a2500..d75d21ee24 100644
--- a/src/libctonfile/parser.rs
+++ b/src/libctonfile/parser.rs
@@ -1,2 +1,202 @@
 
-use cretonne;
+// ====--------------------------------------------------------------------------------------====//
+//
+// Parser for .cton files.
+//
+// ====--------------------------------------------------------------------------------------====//
+
+use std::result;
+use lexer::{self, Lexer, Token};
+use cretonne::{types, repr};
+
+pub use lexer::Location;
+
+/// A parse error is returned when the parse failed.
+pub struct Error {
+    pub location: Location,
+    pub message: String,
+}
+
+pub type Result<T> = result::Result<T, Error>;
+
+pub struct Parser<'a> {
+    lex: Lexer<'a>,
+
+    lex_error: Option<lexer::Error>,
+
+    // Current lookahead token.
+    lookahead: Option<Token<'a>>,
+
+    // Location of lookahead.
+    location: Location,
+}
+
+impl<'a> Parser<'a> {
+    // Consume the current lookahead token and return it.
+    fn consume(&mut self) -> Token<'a> {
+        self.lookahead.take().expect("No token to consume")
+    }
+
+    // Get the current lookahead token, after making sure there is one.
+    fn token(&mut self) -> Option<Token<'a>> {
+        if self.lookahead == None {
+            match self.lex.next() {
+                Some(Ok(lexer::LocatedToken { token, location })) => {
+                    self.lookahead = Some(token);
+                    self.location = location;
+                }
+                Some(Err(lexer::LocatedError { error, location })) => {
+                    self.lex_error = Some(error);
+                    self.location = location;
+                }
+                None => {}
+            }
+        }
+        return self.lookahead;
+    }
+
+    // Generate an error.
+    fn error(&self, message: &str) -> Error {
+        Error {
+            location: self.location,
+            message:
+                // If we have a lexer error latched, report that.
+                match self.lex_error {
+                    Some(lexer::Error::InvalidChar) => "Invalid character".to_string(),
+                    None => message.to_string(),
+                }
+        }
+    }
+
+    // Match and consume a token without payload.
+    fn match_token(&mut self, want: Token<'a>, err_msg: &str) -> Result<Token<'a>> {
+        match self.token() {
+            Some(ref t) if *t == want => Ok(self.consume()),
+            _ => Err(self.error(err_msg)),
+        }
+    }
+
+    // if the next token is a `want`, consume it, otherwise do nothing.
+    fn optional(&mut self, want: Token<'a>) -> bool {
+        match self.token() {
+            Some(t) if t == want => {
+                self.consume();
+                true
+            }
+            _ => false,
+        }
+    }
+
+    // Parse a whole function definition.
+    //
+    // function ::= * "function" name signature { ... }
+    //
+    fn parse_function(&mut self) -> Result<repr::Function> {
+        try!(self.match_token(Token::Function, "Expected 'function' keyword"));
+
+        // function ::= "function" * name signature { ... }
+        let name = try!(self.parse_function_name());
+
+        // function ::= "function" name * signature { ... }
+        let sig = try!(self.parse_signature());
+
+        let mut func = repr::Function::new();
+
+        try!(self.match_token(Token::LBrace, "Expected '{' before function body"));
+        try!(self.match_token(Token::RBrace, "Expected '}' after function body"));
+
+        Ok(func)
+    }
+
+    // Parse a function name.
+    //
+    // function ::= "function" * name signature { ... }
+    //
+    fn parse_function_name(&mut self) -> Result<String> {
+        match self.token() {
+            Some(Token::Identifier(s)) => {
+                self.consume();
+                Ok(s.to_string())
+            }
+            _ => Err(self.error("Expected function name")),
+        }
+    }
+
+    // Parse a function signature.
+    //
+    // signature ::=  * "(" arglist ")" ["->" retlist] [call_conv]
+    // callconv  ::=  string
+    //
+    // function ::= "function" * name signature { ... }
+    //
+    fn parse_signature(&mut self) -> Result<types::Signature> {
+        let mut sig = types::Signature::new();
+
+        try!(self.match_token(Token::LPar, "Expected function signature: '(' args... ')'"));
+        // signature ::=  "(" * arglist ")" ["->" retlist] [call_conv]
+        sig.argument_types = try!(self.parse_argument_list());
+        try!(self.match_token(Token::RPar, "Expected ')' after function arguments"));
+        if self.optional(Token::Arrow) {
+            sig.return_types = try!(self.parse_argument_list());
+            if sig.return_types.is_empty() {
+                return Err(self.error("Missing return type after '->'"));
+            }
+        }
+
+        // TBD: calling convention.
+
+        Ok(sig)
+    }
+
+    // Parse (possibly empty) list of function argument / return value types.
+    //
+    // arglist ::= * <empty>
+    //             * arg
+    //             * arglist "," arg
+    fn parse_argument_list(&mut self) -> Result<Vec<types::ArgumentType>> {
+        let mut list = Vec::new();
+        // arglist   ::= * <empty>
+        //               * arg
+        match self.token() {
+            Some(Token::Type(_)) => list.push(try!(self.parse_argument_type())),
+            _ => return Ok(list),
+        }
+
+        // arglist ::= arg *
+        //             arglist * "," arg
+        while self.token() == Some(Token::Comma) {
+            // arglist ::= arglist * "," arg
+            self.consume();
+            // arglist ::= arglist "," * arg
+            list.push(try!(self.parse_argument_type()));
+        }
+
+        Ok(list)
+    }
+
+    // Parse a single argument type with flags.
+    fn parse_argument_type(&mut self) -> Result<types::ArgumentType> {
+        // arg ::= * type
+        //         * arg flag
+        let mut arg = match self.token() {
+            Some(Token::Type(t)) => types::ArgumentType::new(t),
+            _ => return Err(self.error("Expected argument type")),
+        };
+        loop {
+            self.consume();
+            // arg ::= arg * flag
+            match self.token() {
+                Some(Token::Identifier(s)) => {
+                    match s {
+                        "uext" => arg.extension = types::ArgumentExtension::Uext,
+                        "sext" => arg.extension = types::ArgumentExtension::Sext,
+                        "inreg" => arg.inreg = true,
+                        _ => break,
+                    }
+                }
+                _ => break,
+            }
+        }
+        Ok(arg)
+    }
+}