diff --git a/src/lexer/number.rs b/src/lexer/number.rs
new file mode 100644
index 0000000..0134fbb
--- /dev/null
+++ b/src/lexer/number.rs
@@ -0,0 +1,76 @@
+/* number.rs
+ * Eryn Wells <eryn@erynwells.me>
+ */
+
+struct Number {
+    value: f64,
+}
+
+#[derive(Debug)]
+pub enum Radix { Bin, Oct, Dec, Hex }
+
+#[derive(Debug)]
+pub struct NumberBuilder {
+    exact: bool,
+    radix: Radix,
+    value: f64,
+}
+
+impl NumberBuilder {
+    pub fn new() -> NumberBuilder {
+        NumberBuilder {
+            exact: false,
+            radix: Radix::Dec,
+            value: 0.0,
+        }
+    }
+
+    pub fn exact<'a>(&'a mut self, ex: bool) -> &'a mut Self {
+        self.exact = ex;
+        self
+    }
+
+    pub fn radix<'a>(&'a mut self, r: Radix) -> &'a mut Self {
+        self.radix = r;
+        self
+    }
+
+    pub fn resolve(&self) -> Number {
+        // TODO: Convert fields to Number type.
+        Number { value: 0.0 }
+    }
+
+    pub fn extend_value<'a>(&'a mut self, digit: char) -> &'a mut Self {
+        if let Some(place) = NumberBuilder::place_value(digit) {
+            self.value = self.radix.value() * self.value + place;
+        }
+        else {
+            // TODO: Indicate an error.
+        }
+        self
+    }
+
+    pub fn radix_value(&self) -> u32 {
+        self.radix.value() as u32
+    }
+
+    fn place_value(digit: char) -> Option<f64> {
+        match digit {
+            '0' ... '9' => Some((digit as u32 - '0' as u32) as f64),
+            'a' ... 'f' => Some((digit as u32 - 'a' as u32) as f64),
+            'A' ... 'F' => Some((digit as u32 - 'A' as u32) as f64),
+            _ => None,
+        }
+    }
+}
+
+impl Radix {
+    fn value(&self) -> f64 {
+        match *self {
+            Radix::Bin => 2.0,
+            Radix::Oct => 8.0,
+            Radix::Dec => 10.0,
+            Radix::Hex => 16.0,
+        }
+    }
+}