diff --git a/Cargo.lock b/Cargo.lock
index 91a8c2f..fd3d22a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,12 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "bitflags"
+version = "2.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8f68f53c83ab957f72c32642f3868eec03eb974d1fb82e453128456482613d36"
+
 [[package]]
 name = "bytemuck"
 version = "1.20.0"
@@ -20,6 +26,21 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
+[[package]]
+name = "cfg_aliases"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "613afe47fcd5fac7ccf1db93babcb082c5994d996f20b8b159f2ad1658eb5724"
+
+[[package]]
+name = "clipboard-win"
+version = "5.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "15efe7a882b08f34e38556b14f2fb3daa98769d06c7f0c1b076dfd0d983bc892"
+dependencies = [
+ "error-code",
+]
+
 [[package]]
 name = "colored"
 version = "2.1.0"
@@ -27,7 +48,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cbf2150cce219b664a8a70df7a1f933836724b503f8a413af9365b4dcc4d90b8"
 dependencies = [
  "lazy_static",
- "windows-sys",
+ "windows-sys 0.48.0",
 ]
 
 [[package]]
@@ -40,6 +61,39 @@ dependencies = [
  "fnv",
 ]
 
+[[package]]
+name = "endian-type"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c34f04666d835ff5d62e058c3995147c06f42fe86ff053337632bca83e42702d"
+
+[[package]]
+name = "errno"
+version = "0.3.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "33d852cb9b869c2a9b3df2f71a3074817f01e1844f839a144f5fcef059a4eb5d"
+dependencies = [
+ "libc",
+ "windows-sys 0.59.0",
+]
+
+[[package]]
+name = "error-code"
+version = "3.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a5d9305ccc6942a704f4335694ecd3de2ea531b114ac2d51f5f843750787a92f"
+
+[[package]]
+name = "fd-lock"
+version = "4.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7e5768da2206272c81ef0b5e951a41862938a6070da63bcea197899942d3b947"
+dependencies = [
+ "cfg-if",
+ "rustix",
+ "windows-sys 0.52.0",
+]
+
 [[package]]
 name = "fnv"
 version = "1.0.7"
@@ -57,6 +111,15 @@ dependencies = [
  "wasi",
 ]
 
+[[package]]
+name = "home"
+version = "0.5.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "589533453244b0995c858700322199b2becb13b627df2851f64a2775d024abcf"
+dependencies = [
+ "windows-sys 0.59.0",
+]
+
 [[package]]
 name = "lazy_static"
 version = "1.5.0"
@@ -69,6 +132,18 @@ version = "0.2.164"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "433bfe06b8c75da9b2e3fbea6e5329ff87748f0b144ef75306e674c3f6f7c13f"
 
+[[package]]
+name = "linux-raw-sys"
+version = "0.4.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d26c52dbd32dccf2d10cac7725f8eae5296885fb5703b261f7d0a0739ec807ab"
+
+[[package]]
+name = "log"
+version = "0.4.25"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "04cbf5b083de1c7e0222a7a51dbfdba1cbe1c6ab0b15e29fff3f6c077fd9cd9f"
+
 [[package]]
 name = "memchr"
 version = "2.7.4"
@@ -81,6 +156,27 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "68354c5c6bd36d73ff3feceb05efa59b6acb7626617f4962be322a825e61f79a"
 
+[[package]]
+name = "nibble_vec"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "77a5d83df9f36fe23f0c3648c6bbb8b0298bb5f1939c8f2704431371f4b84d43"
+dependencies = [
+ "smallvec",
+]
+
+[[package]]
+name = "nix"
+version = "0.29.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "71e2746dc3a24dd78b3cfcb7be93368c6de9963d30f43a6a73998a9cf4b17b46"
+dependencies = [
+ "bitflags",
+ "cfg-if",
+ "cfg_aliases",
+ "libc",
+]
+
 [[package]]
 name = "nom"
 version = "7.1.3"
@@ -118,6 +214,16 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "radix_trie"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c069c179fcdc6a2fe24d8d18305cf085fdbd4f922c041943e203685d6a1c58fd"
+dependencies = [
+ "endian-type",
+ "nibble_vec",
+]
+
 [[package]]
 name = "rand"
 version = "0.8.5"
@@ -163,9 +269,51 @@ version = "0.1.0"
 dependencies = [
  "nom",
  "rand",
+ "rustyline",
  "textplots",
 ]
 
+[[package]]
+name = "rustix"
+version = "0.38.44"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fdb5bc1ae2baa591800df16c9ca78619bf65c0488b41b96ccec5d11220d8c154"
+dependencies = [
+ "bitflags",
+ "errno",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys 0.59.0",
+]
+
+[[package]]
+name = "rustyline"
+version = "15.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2ee1e066dc922e513bda599c6ccb5f3bb2b0ea5870a579448f2622993f0a9a2f"
+dependencies = [
+ "bitflags",
+ "cfg-if",
+ "clipboard-win",
+ "fd-lock",
+ "home",
+ "libc",
+ "log",
+ "memchr",
+ "nix",
+ "radix_trie",
+ "unicode-segmentation",
+ "unicode-width",
+ "utf8parse",
+ "windows-sys 0.59.0",
+]
+
+[[package]]
+name = "smallvec"
+version = "1.13.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3c5e1a9a646d36c3599cd173a41282daf47c44583ad367b8e6837255952e5c67"
+
 [[package]]
 name = "syn"
 version = "2.0.89"
@@ -193,6 +341,24 @@ version = "1.0.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "adb9e6ca4f869e1180728b7950e35922a7fc6397f7b641499e8f3ef06e50dc83"
 
+[[package]]
+name = "unicode-segmentation"
+version = "1.12.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f6ccf251212114b54433ec949fd6a7841275f9ada20dddd2f29e9ceea4501493"
+
+[[package]]
+name = "unicode-width"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1fc81956842c57dac11422a97c3b8195a1ff727f06e85c84ed2e8aa277c9a0fd"
+
+[[package]]
+name = "utf8parse"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "06abde3611657adf66d383f00b093d7faecc7fa57071cce2578660c9f1010821"
+
 [[package]]
 name = "wasi"
 version = "0.11.0+wasi-snapshot-preview1"
@@ -205,7 +371,25 @@ version = "0.48.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "677d2418bec65e3338edb076e806bc1ec15693c5d0104683f2efe857f61056a9"
 dependencies = [
- "windows-targets",
+ "windows-targets 0.48.5",
+]
+
+[[package]]
+name = "windows-sys"
+version = "0.52.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "282be5f36a8ce781fad8c8ae18fa3f9beff57ec1b52cb3de0789201425d9a33d"
+dependencies = [
+ "windows-targets 0.52.6",
+]
+
+[[package]]
+name = "windows-sys"
+version = "0.59.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e38bc4d79ed67fd075bcc251a1c39b32a1776bbe92e5bef1f0bf1f8c531853b"
+dependencies = [
+ "windows-targets 0.52.6",
 ]
 
 [[package]]
@@ -214,13 +398,29 @@ version = "0.48.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9a2fa6e2155d7247be68c096456083145c183cbbbc2764150dda45a87197940c"
 dependencies = [
- "windows_aarch64_gnullvm",
- "windows_aarch64_msvc",
- "windows_i686_gnu",
- "windows_i686_msvc",
- "windows_x86_64_gnu",
- "windows_x86_64_gnullvm",
- "windows_x86_64_msvc",
+ "windows_aarch64_gnullvm 0.48.5",
+ "windows_aarch64_msvc 0.48.5",
+ "windows_i686_gnu 0.48.5",
+ "windows_i686_msvc 0.48.5",
+ "windows_x86_64_gnu 0.48.5",
+ "windows_x86_64_gnullvm 0.48.5",
+ "windows_x86_64_msvc 0.48.5",
+]
+
+[[package]]
+name = "windows-targets"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9b724f72796e036ab90c1021d4780d4d3d648aca59e491e6b98e725b84e99973"
+dependencies = [
+ "windows_aarch64_gnullvm 0.52.6",
+ "windows_aarch64_msvc 0.52.6",
+ "windows_i686_gnu 0.52.6",
+ "windows_i686_gnullvm",
+ "windows_i686_msvc 0.52.6",
+ "windows_x86_64_gnu 0.52.6",
+ "windows_x86_64_gnullvm 0.52.6",
+ "windows_x86_64_msvc 0.52.6",
 ]
 
 [[package]]
@@ -229,42 +429,90 @@ version = "0.48.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2b38e32f0abccf9987a4e3079dfb67dcd799fb61361e53e2882c3cbaf0d905d8"
 
+[[package]]
+name = "windows_aarch64_gnullvm"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32a4622180e7a0ec044bb555404c800bc9fd9ec262ec147edd5989ccd0c02cd3"
+
 [[package]]
 name = "windows_aarch64_msvc"
 version = "0.48.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "dc35310971f3b2dbbf3f0690a219f40e2d9afcf64f9ab7cc1be722937c26b4bc"
 
+[[package]]
+name = "windows_aarch64_msvc"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09ec2a7bb152e2252b53fa7803150007879548bc709c039df7627cabbd05d469"
+
 [[package]]
 name = "windows_i686_gnu"
 version = "0.48.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a75915e7def60c94dcef72200b9a8e58e5091744960da64ec734a6c6e9b3743e"
 
+[[package]]
+name = "windows_i686_gnu"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e9b5ad5ab802e97eb8e295ac6720e509ee4c243f69d781394014ebfe8bbfa0b"
+
+[[package]]
+name = "windows_i686_gnullvm"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0eee52d38c090b3caa76c563b86c3a4bd71ef1a819287c19d586d7334ae8ed66"
+
 [[package]]
 name = "windows_i686_msvc"
 version = "0.48.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8f55c233f70c4b27f66c523580f78f1004e8b5a8b659e05a4eb49d4166cca406"
 
+[[package]]
+name = "windows_i686_msvc"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "240948bc05c5e7c6dabba28bf89d89ffce3e303022809e73deaefe4f6ec56c66"
+
 [[package]]
 name = "windows_x86_64_gnu"
 version = "0.48.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "53d40abd2583d23e4718fddf1ebec84dbff8381c07cae67ff7768bbf19c6718e"
 
+[[package]]
+name = "windows_x86_64_gnu"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "147a5c80aabfbf0c7d901cb5895d1de30ef2907eb21fbbab29ca94c5b08b1a78"
+
 [[package]]
 name = "windows_x86_64_gnullvm"
 version = "0.48.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0b7b52767868a23d5bab768e390dc5f5c55825b6d30b86c844ff2dc7414044cc"
 
+[[package]]
+name = "windows_x86_64_gnullvm"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "24d5b23dc417412679681396f2b49f3de8c1473deb516bd34410872eff51ed0d"
+
 [[package]]
 name = "windows_x86_64_msvc"
 version = "0.48.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ed94fce61571a4006852b7389a063ab983c02eb1bb37b47f8272ce92d06d9538"
 
+[[package]]
+name = "windows_x86_64_msvc"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "589f6da84c646204747d1270a2a5661ea66ed1cced2631d546fdfb155959f9ec"
+
 [[package]]
 name = "zerocopy"
 version = "0.7.35"
diff --git a/Cargo.toml b/Cargo.toml
index 2fd91d8..79b2e22 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,4 +6,5 @@ edition = "2021"
 [dependencies]
 nom = "7.1.3"
 rand = "0.8.5"
+rustyline = "15.0.0"
 textplots = "0.8.6"
diff --git a/src/bucket.rs b/src/bucket.rs
index 701c93d..94d38e4 100644
--- a/src/bucket.rs
+++ b/src/bucket.rs
@@ -40,6 +40,18 @@ impl<const S: usize> Buckets<S> {
         self._buckets[pp] += 1;
     }
 
+    pub fn percent(&self, val: i64) -> f64 {
+        let mut total = 0;
+        let mut less_than = 0;
+        for i in 0..self._buckets.len() {
+            total += self._buckets[i];
+            if self._offsets[i] < val {
+                less_than += self._buckets[i];
+            }
+        }
+        less_than as f64 / total as f64
+    }
+
     pub fn buckets(&self) -> &[u64] {
         &self._buckets[..]
     }
@@ -51,4 +63,4 @@ impl<const S: usize> Buckets<S> {
     pub fn max(&self) -> u64 {
         *self._buckets.iter().max().unwrap()
     }
-}
\ No newline at end of file
+}
diff --git a/src/main.rs b/src/main.rs
index de0b70a..ce025ce 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,15 +1,25 @@
 use rand::thread_rng;
 use rust_roller::{Buckets, Roller};
-use std::io::{self, BufRead, Write};
+use std::io::{self, Write};
 use textplots::{Chart, Plot, Shape};
+use rustyline::error::ReadlineError;
+use rustyline::DefaultEditor;
 
 fn main() {
     let mut roller = Roller::default();
-    let stdin = io::stdin();
-    print!("> ");
+    let mut rl = DefaultEditor::new().unwrap();
     io::stdout().flush().unwrap();
-    for line in stdin.lock().lines() {
-        let line = line.unwrap();
+    loop {
+        let readline = rl.readline("> ");
+        let line = match readline {
+            Ok(line) => line,
+            Err(ReadlineError::Interrupted) | Err(ReadlineError::Eof) => break,
+            Err(e) => {
+                println!("Error {:?}", e);
+                continue;
+            },
+        };
+        rl.add_history_entry(line.as_str()).unwrap();
         match roller.parse(&line) {
             Ok(r) => r,
             Err(e) => {
@@ -40,6 +50,10 @@ fn main() {
         )
         .lineplot(&Shape::Bars(&points))
         .display();
+        // Roll one dice
+        let ans = roller.roll(&mut thread_rng());
+        // println!("Roller: {:?}", roller);
+        println!("You rolled {} (p={})", ans, bins.percent(ans));
         print!("> ");
         io::stdout().flush().unwrap();
     }
diff --git a/src/roller.rs b/src/roller.rs
index baad43c..8243cf7 100644
--- a/src/roller.rs
+++ b/src/roller.rs
@@ -3,6 +3,7 @@ use nom::{
 };
 use rand::Rng;
 
+#[derive(Debug)]
 pub struct Roller<const S: usize> {
     exprs: [Option<Cmd>; S],
 }
@@ -34,8 +35,8 @@ impl<const S: usize> Roller<S> {
         // Implementation detail of this struct; we don't zero out the
         // expression between parses, instead, just set the n+1 one to
         // None. This will cause roll to stop. 
-        if limit+1 < self.exprs.len() {
-            self.exprs[limit+1] = None;
+        if limit < self.exprs.len() {
+            self.exprs[limit] = None;
         }
         Ok(())
     }
@@ -112,11 +113,13 @@ fn parse<'a, 'b>(mut expr: &'a str, exprs: &'b mut [Option<Cmd>]) -> Result<usiz
     Ok(i)
 }
 
+#[derive(Debug)]
 struct Cmd {
     oper: Oper,
     term: Term,
 }
 
+#[derive(Debug)]
 enum Term {
     Roll(Roll),
     Const(u64),
@@ -145,12 +148,13 @@ impl Term {
     }
 }
 
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Debug)]
 enum Oper {
     Add,
     Sub,
 }
 
+#[derive(Debug)]
 struct Roll {
     reps: u64,
     dice: u64,
@@ -229,4 +233,4 @@ mod tests {
         parse("1d8 + 1d8 + 2", &mut exprs)?;
         Ok(())
     }
-}
\ No newline at end of file
+}