diff --git a/src/mango/util/parsetxt/int.rs b/src/mango/util/parsetxt/int.rs
index d2d22b55..0408acf0 100644
--- a/src/mango/util/parsetxt/int.rs
+++ b/src/mango/util/parsetxt/int.rs
@@ -1,21 +1,63 @@
+use mango::util::strslice::char_ops::char_drop;
 use regex::Regex;
 
+#[derive(Debug)]
+pub enum IntParseFailReason {
+    Invalid,
+    Overflow,
+    Underflow,
+}
+
 /// This matches integer literals, either just numbers in base 10, or base 2-36 with prefix.
 /// The syntax for -37 in base 16 is -16b25 and 2748 is 16bABC.
 /// Incorrect values like 4b7 or 0b0 are not handled at the lexing stage.
 pub fn int_pattern() -> &'static str {
-    r"(?:\+|-*)(?:[1-9][0-9]*b(?:_?[0-9a-zA-Z])+|[0-9](?:_?[0-9])*)"
+    r"(?P<sign>\+|-?)(?:(?P<base>[1-9][0-9]*)b(?P<reb_val>(?:_?[0-9a-zA-Z])+)|(?P<b10_val>[0-9](?:_?[0-9])*))"
 }
 
 /// Convert a String that matches [int_pattern] to an i64 integer. Overflow is possible.
-pub fn parse_int<S: Into<String>>(text: S) -> Option<i64> {
+pub fn parse_int<S: Into<String>>(text: S) -> Result<i64, IntParseFailReason> {
     let text = text.into();
-    debug_assert!(
-        Regex::new(&format!("^{}$", int_pattern()))
-            .unwrap()
-            .is_match(&text)
-    );
-    Some(0i64)
+    match Regex::new(&format!("^{}$", int_pattern()))
+        .unwrap()
+        .captures(&text)
+    {
+        None => return Err(IntParseFailReason::Invalid),
+        Some(captures) => {
+            // Sign
+            let sign_str = captures.name("sign").unwrap().as_str();
+            let sign = if sign_str == "+" || sign_str == "" {
+                1 // positive
+            } else {
+                -1 // negative
+            };
+            // Check if base10 or special
+            match captures.name("b10_val") {
+                None => {
+                    // There is a base provided.
+                    if let Some(base) = captures.name("base") {
+                        if let Some(value) = captures.name("reb_val") {
+                            // TODO: implement
+                            panic!(format!(
+                                "Do not yet know how to deal with {} in base {}",
+                                char_drop(value.as_str(), &'_'),
+                                base.as_str()
+                            ))
+                        } else {
+                            panic!("Expected 'reb_val' match in regex")
+                        }
+                    } else {
+                        panic!("Expected 'base' match in regex")
+                    }
+                }
+                Some(value) => {
+                    // This is a 'normal' (base10) value.
+                    // TODO: check for over/underflow
+                    return Ok(char_drop(value.as_str(), &'_').parse::<i64>().unwrap());
+                }
+            }
+        }
+    }
 }
 
 // TODO: possibly add a i32 version?
@@ -27,6 +69,8 @@ mod tests {
 
     #[test]
     fn test_parse_int() {
-        assert_eq!(42, parse_int("42").unwrap())
+        assert_eq!(42, parse_int("42").unwrap());
+        assert_eq!(42, parse_int("4_2").unwrap());
+        // assert_eq!(42, parse_int("10b4_2").unwrap());
     }
 }
diff --git a/src/mango/util/parsetxt/real.rs b/src/mango/util/parsetxt/real.rs
index 9d858a55..1ba756c6 100644
--- a/src/mango/util/parsetxt/real.rs
+++ b/src/mango/util/parsetxt/real.rs
@@ -1,5 +1,13 @@
 use regex::Regex;
 
+#[derive(Debug)]
+pub enum RealParseFailReason {
+    Invalid,
+    Overflow,
+    Underflow,
+    PrecisionLoss(f64),
+}
+
 /// This matches real literals (base 10), which look like this:
 ///   sign / int1 / period / int2 / e / sign / int
 /// Here int is a series of 0-9 digits separated by at most one underscore.
@@ -8,18 +16,18 @@ pub fn real_pattern() -> &'static str {
     // TODO: do I want to allow numbers to start with a period?
     // TODO: for now, only base10 for reals (would 8b11e2 be 9*8^2 or 9*10^2?)
     // TODO: does not deal with NaN of infinity
-    r"(?:\+|-*)(?:\d(?:_?\d)*\.\d(?:_?\d)*|\d(?:_?\d)*\.|\.\d(?:_?\d)*)(?:e(?:\+|-|)\d(?:_?\d)*)?"
+    r"(?P<sign>\+|-?)(?:\d(?:_?\d)*\.\d(?:_?\d)*|\d(?:_?\d)*\.|\.\d(?:_?\d)*)(?:e(?P<exp_sign>\+|-?)\d(?:_?\d)*)?"
 }
 
 /// Convert a String that matches [real_pattern] to an f64 real. Overflow and loss of precision is possible.
-pub fn parse_real<S: Into<String>>(text: S) -> Option<f64> {
+pub fn parse_real<S: Into<String>>(text: S) -> Result<f64, RealParseFailReason> {
     let text = text.into();
     debug_assert!(
         Regex::new(&format!("^{}$", real_pattern()))
             .unwrap()
             .is_match(&text)
     );
-    Some(0.0f64)
+    Ok(0.0f64)
 }
 
 // TODO: possibly add a i32 version?
@@ -30,7 +38,7 @@ mod tests {
     use super::parse_real;
 
     #[test]
-    fn test_parse_int() {
+    fn test_parse_real() {
         assert_eq!(42., parse_real("42.").unwrap())
     }
 }
diff --git a/src/mango/util/strslice/char_ops.rs b/src/mango/util/strslice/char_ops.rs
new file mode 100644
index 00000000..a2e351f4
--- /dev/null
+++ b/src/mango/util/strslice/char_ops.rs
@@ -0,0 +1,6 @@
+/// Remove all matching characters from the string.
+// Signature may be changed to support a set of characters, if the need arises.
+pub fn char_drop<S: Into<String>>(text: S, strip: &char) -> String {
+    let text = text.into();
+    text.chars().filter(|chr| chr != strip).collect()
+}
diff --git a/src/mango/util/strslice/mod.rs b/src/mango/util/strslice/mod.rs
index 5846d94a..08a0519c 100644
--- a/src/mango/util/strslice/mod.rs
+++ b/src/mango/util/strslice/mod.rs
@@ -2,3 +2,5 @@ pub mod slice;
 pub use self::slice::charslice;
 pub use self::slice::charslicefrom;
 pub use self::slice::charsliceto;
+
+pub mod char_ops;