diff --git a/lexer/src/states/number/digit.rs b/lexer/src/states/number/digit.rs
new file mode 100644
index 0000000..d571cbb
--- /dev/null
+++ b/lexer/src/states/number/digit.rs
@@ -0,0 +1,44 @@
+/* lexer/src/states/number/digit.rs
+ * Eryn Wells <eryn@erynwells.me>
+ */
+
+use chars::Lexable;
+use error::Error;
+use states::{State, StateResult};
+use states::number::{Builder, Radix, Exact};
+use states::number::sign::Sign;
+use token::Token;
+
+#[derive(Debug)] pub struct Digit(Builder);
+
+impl Digit {
+    pub fn new(b: Builder) -> Digit {
+        Digit(b)
+    }
+
+    pub fn with_char(b: Builder, c: char) -> Option<Digit> {
+        let mut b = b.clone();
+        if !b.seen_radix() {
+            b.push_radix(Radix::Dec);
+        }
+        match b.push_digit(c) {
+            Ok(_) => Some(Digit::new(b)),
+            // TODO: Deal with this error properly. Don't just ignore it.
+            Err(_) => None,
+        }
+    }
+}
+
+impl State for Digit {
+    fn lex(&mut self, c: char) -> StateResult {
+        if self.0.push_digit(c).is_ok() {
+            StateResult::Continue
+        } else {
+            StateResult::fail(Error::invalid_char(c))
+        }
+    }
+
+    fn none(&mut self) -> Result<Option<Token>, Error> {
+        Err(Error::unexpected_eof())
+    }
+}
diff --git a/lexer/src/states/number/mod.rs b/lexer/src/states/number/mod.rs
index 27d0315..daeecde 100644
--- a/lexer/src/states/number/mod.rs
+++ b/lexer/src/states/number/mod.rs
@@ -2,24 +2,14 @@
  * Eryn Wells <eryn@erynwells.me>
  */
 
+use error::Error;
+
+mod digit;
 mod prefix;
 mod sign;
 
 pub use self::prefix::Prefix;
 
-trait NumberLexable {
-    /// Returns the value of this character interpreted as the indicator for a
-    /// base. In Scheme, you indicate the base of a number by prefixing it with
-    /// #[bodx].
-    fn base_value(&self) -> Option<Radix>;
-    /// Returns the value of the character interpreted as a numerical digit.
-    fn digit_value(&self) -> Option<u8>;
-    fn sign_value(&self) -> Option<Sign>;
-    fn is_dot(&self) -> bool;
-    fn is_hash(&self) -> bool;
-    fn is_sign(&self) -> bool;
-}
-
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub enum Radix { Bin = 2, Oct = 8, Dec = 10, Hex = 16 }
 
@@ -65,12 +55,19 @@ impl Builder {
              radix: None,
              sign: None,
              exact: None,
-             value: 0
+             value: 0,
         }
     }
 
-    fn push_digit(&mut self, digit: u8) {
-        //self.value = self.value * self.base_value() as i64 + digit as i64;
+    fn push_digit(&mut self, c: char) -> Result<(), Error> {
+        let rx = self.radix_value();
+        match c.to_digit(rx as u32) {
+            Some(d) => {
+                self.value = self.value * rx as i64 + d as i64;
+                Ok(())
+            },
+            None => Err(Error::invalid_char(c))
+        }
     }
 
     fn push_exact(&mut self, ex: Exact) {
@@ -94,4 +91,12 @@ impl Builder {
     fn seen_exact(&self) -> bool { self.exact.is_some() }
     fn seen_radix(&self) -> bool { self.radix.is_some() }
     fn seen_sign(&self) -> bool { self.sign.is_some() }
+
+    fn radix_value(&self) -> u8 {
+        let rx = match self.radix {
+            Some(r) => r,
+            None => Radix::Dec,
+        };
+        rx as u8
+    }
 }
diff --git a/lexer/src/states/number/prefix.rs b/lexer/src/states/number/prefix.rs
index dddadfa..6003b81 100644
--- a/lexer/src/states/number/prefix.rs
+++ b/lexer/src/states/number/prefix.rs
@@ -50,7 +50,7 @@ impl State for Prefix {
     }
 
     fn none(&mut self) -> Result<Option<Token>, Error> {
-        Err(Error::new("blah".to_string()))
+        Err(Error::unexpected_eof())
     }
 }