diff --git a/Cargo.lock b/Cargo.lock
index 7d6666c..834c788 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -280,7 +280,7 @@ dependencies = [
 
 [[package]]
 name = "rustcalc"
-version = "1.4.1"
+version = "1.5.0"
 dependencies = [
  "colored",
  "dirs",
diff --git a/Cargo.toml b/Cargo.toml
index b5cfc65..25154bc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "rustcalc"
-version = "1.4.1"
+version = "1.5.0"
 authors = ["George-Lewis <georgejeffreylewis@gmail.com>"]
 edition = "2018"
 description = "A command-line utility for evaluating mathematical statements"
diff --git a/src/cli/editor/completer.rs b/src/cli/editor/completer.rs
new file mode 100644
index 0000000..a64d97b
--- /dev/null
+++ b/src/cli/editor/completer.rs
@@ -0,0 +1,49 @@
+use rustyline::completion::{Completer, Pair};
+
+use super::{
+    finder::{find_items, Findable},
+    MyHelper,
+};
+
+fn find_candidates<Item: Findable>(line: &str, items: &[Item]) -> Option<Vec<Pair>> {
+    let create_intermediate = |stride, item: &Item| {
+        let replacement = item.replacement()[stride..].to_string();
+        let display = item.format();
+        Pair {
+            display,
+            replacement,
+        }
+    };
+    find_items(line, items, create_intermediate)
+}
+
+impl Completer for MyHelper<'_> {
+    type Candidate = Pair;
+
+    fn complete(
+        &self,
+        line: &str,
+        pos: usize,
+        _ctx: &rustyline::Context<'_>,
+    ) -> rustyline::Result<(usize, Vec<Self::Candidate>)> {
+        let line = &line[..pos];
+
+        let funcs = self.funcs.borrow();
+        let vars = self.vars.borrow();
+
+        let candidates = if let Some(candidates) = find_candidates(line, &funcs) {
+            (pos, candidates)
+        } else if let Some(candidates) = find_candidates(line, &vars) {
+            (pos, candidates)
+        } else {
+            (0, vec![])
+        };
+
+        rustyline::Result::Ok(candidates)
+    }
+
+    fn update(&self, line: &mut rustyline::line_buffer::LineBuffer, start: usize, elected: &str) {
+        let end = line.pos();
+        line.replace(start..end, elected);
+    }
+}
diff --git a/src/cli/editor/finder.rs b/src/cli/editor/finder.rs
new file mode 100644
index 0000000..e4d9d5c
--- /dev/null
+++ b/src/cli/editor/finder.rs
@@ -0,0 +1,128 @@
+use std::borrow::Cow;
+
+use rustmatheval::model::{
+    functions::{Function, PREFIX as FUNCTION_PREFIX},
+    variables::{Variable, PREFIX as VARIABLE_PREFIX},
+};
+
+use crate::funcs::format_func_with_args;
+use crate::vars::format_var_name;
+
+/// Find the position of the last instance of `c`
+///
+/// ## Examples
+///
+/// ```
+/// use  rustmatheval::model::functions::PREFIX;
+/// let s = format1("abc {}foo bar", PREFIX);
+/// let pos = find_last(PREFIX, s).unwrap();
+/// assert_eq!(s.chars().nth(pos), PREFIX);
+/// ```
+pub fn find_last(c: char, str: &str) -> Option<usize> {
+    str.chars()
+        .into_iter()
+        .rev()
+        .position(|ch| ch == c)
+        .map(|pos| str.chars().count() - pos - 1)
+}
+
+/// Find all possibly completable `Item`s in `line` at the position closest to the end as indicated by [`Findable::prefix`]
+/// and perform transformations on it using the two `Fn` parameters.
+///
+/// ## Parameters
+/// * `Item` - A [`Findable`] type to search for in `line`
+/// * `Intermediate` - The output type
+/// * `ToIntermediate` - A `Fn` type capable of converting `Item`s to `Intermediate`
+///
+/// ## Arguments
+/// * `line` - The string to find items within
+/// * `items` - A slice of items, these are candidates for the search
+/// * `create_intermediate` - A `Fn` that:
+///   * accepts:
+///     * `stride: usize`: The stride of the matching section
+///     * `item: &Item`: The matching item
+///   * and produces an `Intermediate`
+///
+/// ## Returns
+/// Returns `None` if there are no possible matches inside the input stringThere are two reasons this could occur:
+///   * There is no prefix in the string, and thus no matches are possible
+///   * There is a prefix in the string, but none of the items could possibly complete the identifier
+///
+/// Otherwise: Returns a vector of intermediates
+pub(super) fn find_items<Item, Intermediate, ToIntermediate>(
+    line: &str,
+    items: &[Item],
+    create_intermediate: ToIntermediate,
+) -> Option<Vec<Intermediate>>
+where
+    Item: Findable,
+    ToIntermediate: Fn(usize, &Item) -> Intermediate,
+{
+    if let Some(pos) = find_last(Item::prefix(), line) {
+        // +1 removes prefix
+        // e.g. "#foobar" => "foobar"
+        let line = &line[pos + 1..];
+        let stride = line.len();
+
+        let matches: Vec<Intermediate> = items
+            .iter()
+            .filter(|it| it.name().starts_with(line))
+            .map(|it| create_intermediate(stride, it))
+            .collect();
+        if !matches.is_empty() {
+            return Some(matches);
+        }
+    }
+    None
+}
+
+/// Represents a type that can be found (using [`find_items`])
+pub trait Findable {
+    fn name(&self) -> &str;
+    fn replacement(&self) -> Cow<'_, str>;
+    fn format(&self) -> String;
+    fn prefix() -> char;
+}
+
+impl Findable for Function {
+    fn name(&self) -> &str {
+        &self.name
+    }
+
+    fn replacement(&self) -> Cow<'_, str> {
+        let appendix = if self.arity() == 0 {
+            // If the function takes no arguments we can just open and close the parens
+            "()"
+        } else {
+            "("
+        };
+        let formatted = format!("{}{}", &self.name, appendix);
+        Cow::Owned(formatted)
+    }
+
+    fn format(&self) -> String {
+        format_func_with_args(self)
+    }
+
+    fn prefix() -> char {
+        FUNCTION_PREFIX
+    }
+}
+
+impl Findable for Variable {
+    fn name(&self) -> &str {
+        &self.repr
+    }
+
+    fn replacement(&self) -> Cow<'_, str> {
+        Cow::Borrowed(&self.repr)
+    }
+
+    fn format(&self) -> String {
+        format_var_name(&self.repr).to_string()
+    }
+
+    fn prefix() -> char {
+        VARIABLE_PREFIX
+    }
+}
diff --git a/src/cli/editor/highlighter.rs b/src/cli/editor/highlighter.rs
new file mode 100644
index 0000000..890d70b
--- /dev/null
+++ b/src/cli/editor/highlighter.rs
@@ -0,0 +1,37 @@
+use std::borrow::Cow;
+
+use colored::Colorize;
+use rustyline::highlight::Highlighter;
+
+use super::MyHelper;
+
+impl Highlighter for MyHelper<'_> {
+    fn highlight<'l>(&self, line: &'l str, _pos: usize) -> std::borrow::Cow<'l, str> {
+        Cow::Borrowed(line)
+    }
+
+    fn highlight_prompt<'b, 's: 'b, 'p: 'b>(
+        &'s self,
+        prompt: &'p str,
+        _default: bool,
+    ) -> std::borrow::Cow<'b, str> {
+        Cow::Borrowed(prompt)
+    }
+
+    fn highlight_hint<'h>(&self, hint: &'h str) -> std::borrow::Cow<'h, str> {
+        Cow::Owned(hint.black().on_white().to_string())
+    }
+
+    fn highlight_candidate<'c>(
+        &self,
+        candidate: &'c str,
+        _completion: rustyline::CompletionType,
+    ) -> std::borrow::Cow<'c, str> {
+        // We don't highlight the candidate because the completer formats with color
+        Cow::Borrowed(candidate)
+    }
+
+    fn highlight_char(&self, _line: &str, _pos: usize) -> bool {
+        true
+    }
+}
diff --git a/src/cli/editor/hinter.rs b/src/cli/editor/hinter.rs
new file mode 100644
index 0000000..2652b39
--- /dev/null
+++ b/src/cli/editor/hinter.rs
@@ -0,0 +1,25 @@
+use rustyline::hint::Hinter;
+
+use super::{
+    finder::{find_items, Findable},
+    MyHelper,
+};
+
+pub fn find_hint<Item: Findable>(line: &str, items: &[Item]) -> Option<String> {
+    let create_intermediate = |stride, item: &Item| item.replacement()[stride..].to_string();
+    let hints = find_items(line, items, create_intermediate);
+    hints.and_then(|hints| hints.into_iter().max_by_key(String::len))
+}
+
+impl Hinter for MyHelper<'_> {
+    type Hint = String;
+
+    fn hint(&self, line: &str, pos: usize, _ctx: &rustyline::Context<'_>) -> Option<Self::Hint> {
+        let line = &line[..pos];
+
+        let funcs = self.funcs.borrow();
+        let vars = self.vars.borrow();
+
+        find_hint(line, &funcs).or_else(|| find_hint(line, &vars))
+    }
+}
diff --git a/src/cli/editor/mod.rs b/src/cli/editor/mod.rs
new file mode 100644
index 0000000..e108142
--- /dev/null
+++ b/src/cli/editor/mod.rs
@@ -0,0 +1,32 @@
+use std::cell::RefCell;
+
+use rustmatheval::model::{functions::Function, variables::Variable};
+use rustyline::{config::Configurer, Editor, Helper};
+
+mod completer;
+mod finder;
+mod highlighter;
+mod hinter;
+mod validator;
+
+pub fn editor<'a>(
+    funcs: &'a RefCell<Vec<Function>>,
+    vars: &'a RefCell<Vec<Variable>>,
+) -> Editor<MyHelper<'a>> {
+    let mut editor = Editor::<MyHelper>::new();
+
+    let helper = MyHelper { funcs, vars };
+
+    editor.set_helper(Some(helper));
+
+    editor.set_completion_type(rustyline::CompletionType::List);
+
+    editor
+}
+
+pub struct MyHelper<'cell> {
+    pub funcs: &'cell RefCell<Vec<Function>>,
+    pub vars: &'cell RefCell<Vec<Variable>>,
+}
+
+impl Helper for MyHelper<'_> {}
diff --git a/src/cli/editor/validator.rs b/src/cli/editor/validator.rs
new file mode 100644
index 0000000..8ad5665
--- /dev/null
+++ b/src/cli/editor/validator.rs
@@ -0,0 +1,16 @@
+use rustyline::validate::{ValidationResult, Validator};
+
+use super::MyHelper;
+
+impl Validator for MyHelper<'_> {
+    fn validate(
+        &self,
+        _ctx: &mut rustyline::validate::ValidationContext,
+    ) -> rustyline::Result<ValidationResult> {
+        Ok(rustyline::validate::ValidationResult::Valid(None))
+    }
+
+    fn validate_while_typing(&self) -> bool {
+        false
+    }
+}
diff --git a/src/cli/funcs.rs b/src/cli/funcs.rs
index fecbd75..78c5074 100644
--- a/src/cli/funcs.rs
+++ b/src/cli/funcs.rs
@@ -41,11 +41,18 @@ pub fn format_func_name(name: &str) -> ColoredString {
     format!("#{}", name.magenta().bold()).normal()
 }
 
-fn format_func(func: &Function, funcs: &[Function], vars: &[Variable]) -> String {
+pub fn format_func_with_args(func: &Function) -> String {
     format!(
-        "[ {}({}) = {} ]",
+        "{}({})",
         format_func_name(&func.name),
-        func.args.iter().map(color_arg).join(", "),
+        func.args.iter().map(color_arg).join(", ")
+    )
+}
+
+fn format_func(func: &Function, funcs: &[Function], vars: &[Variable]) -> String {
+    format!(
+        "[ {} = {} ]",
+        format_func_with_args(func),
         stringify_func_code(func, funcs, vars)
     )
 }
diff --git a/src/cli/main.rs b/src/cli/main.rs
index 8368ca1..16e389e 100644
--- a/src/cli/main.rs
+++ b/src/cli/main.rs
@@ -2,6 +2,7 @@
 
 mod cli;
 mod config;
+mod editor;
 mod error;
 mod funcs;
 mod rcfile;
@@ -13,14 +14,13 @@ use lib::{doeval, model::EvaluationContext};
 pub use rustmatheval as lib;
 
 use config::HISTORY_FILE;
-use rustyline::Editor;
 
 use error::Error;
-use std::{env, process};
+use std::{cell::RefCell, env, process};
 
 use cli::{handle_errors, handle_input};
 
-use crate::cli::handle_library_errors;
+use crate::{cli::handle_library_errors, editor::editor};
 
 pub fn main() -> ! {
     // One-shot mode
@@ -51,10 +51,10 @@ pub fn main() -> ! {
         process::exit(code);
     }
 
-    let mut vars = vec![];
-    let mut funcs = vec![];
+    let vars = RefCell::new(vec![]);
+    let funcs = RefCell::new(vec![]);
 
-    if let Err(inner) = rcfile::load(&mut vars, &mut funcs) {
+    if let Err(inner) = rcfile::load(&mut vars.borrow_mut(), &mut funcs.borrow_mut()) {
         match inner {
             Error::Io(inner) => {
                 println!("Error loading RCFile: {:#?}", inner);
@@ -63,7 +63,7 @@ pub fn main() -> ! {
         }
     };
 
-    let mut editor = Editor::<()>::new();
+    let mut editor = editor(&funcs, &vars);
 
     if let Some(path) = HISTORY_FILE.as_deref() {
         editor.load_history(path).ok();
@@ -88,7 +88,7 @@ pub fn main() -> ! {
         // Add the line to the history
         editor.add_history_entry(&input);
 
-        match handle_input(&input, &mut vars, &mut funcs) {
+        match handle_input(&input, &mut vars.borrow_mut(), &mut funcs.borrow_mut()) {
             Ok(formatted) => println!("{}", formatted),
             Err(error) => {
                 let msg = handle_errors(&error, &input);
diff --git a/src/lib/model/functions.rs b/src/lib/model/functions.rs
index a651e36..7623352 100644
--- a/src/lib/model/functions.rs
+++ b/src/lib/model/functions.rs
@@ -8,6 +8,8 @@ use super::{
     EvaluationContext,
 };
 
+pub const PREFIX: char = '#';
+
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub enum Functions<'a> {
     Builtin(&'a Operator),
@@ -61,7 +63,7 @@ impl Searchable for Function {
 
 impl Function {
     pub fn is(text: &str) -> bool {
-        text.starts_with('#')
+        text.starts_with(PREFIX)
     }
     pub fn next_function<'a>(text: &str, funcs: &'a [Self]) -> Option<(&'a Self, usize)> {
         get_by_repr(text, funcs)
diff --git a/src/lib/model/variables.rs b/src/lib/model/variables.rs
index e9b9fbf..2cb0e27 100644
--- a/src/lib/model/variables.rs
+++ b/src/lib/model/variables.rs
@@ -1,5 +1,7 @@
 use super::representable::{get_by_repr, Searchable};
 
+pub const PREFIX: char = '$';
+
 #[derive(Clone, Debug, PartialEq)]
 /// Represents a variable, a value with a name
 pub struct Variable {
@@ -29,7 +31,7 @@ impl Variable {
 
     /// Returns whether or not the given representation could reference a valid variable
     pub fn is(repr: &str) -> bool {
-        repr.starts_with('$')
+        repr.starts_with(PREFIX)
     }
 }