feat: return Result instead of panicking

this doesn't always work still;
there are a lot of panicking index operations there.

a feature was stabilized very recently that would help fix that:
https://github.com/rust-lang/rust/issues/146954

src/formatting.rs

@@ -2,9 +2,9 @@ use std::str::FromStr;
 
 use rug::Float;
 
-use crate::nodes::Nodes;
+use crate::nodes::{Error, Nodes};
 
-pub fn pretty_eval(mut input: String) -> String {
+pub fn pretty_eval(mut input: String) -> Result<String, Error> {
     // no need to remove the characters here,
     // as we ignore the them in all other logic already
     let should_add_back_alignment = input.contains('&');
@@ -18,10 +18,10 @@ pub fn pretty_eval(mut input: String) -> String {
         })
         .is_some();
 
-    let result = Nodes::from_str(&input).unwrap().evaluate();
+    let result = Nodes::from_str(&input)?.evaluate()?;
     let significant_digits = get_significant_digits(&result);
 
-    format!(
+    Ok(format!(
         "{:leading_spaces$}{}{result:.significant_digits$}{}",
         ' ',
         if should_add_back_equals && should_add_back_alignment {
@@ -34,14 +34,14 @@ pub fn pretty_eval(mut input: String) -> String {
             ""
         },
         if should_add_back_backslash { " \\" } else { "" }
-    )
+    ))
 }
 #[test]
 fn test_character_readdition() {
-    assert_eq!(pretty_eval(" = 11".into()), " = 11");
-    assert_eq!(pretty_eval(" &= 11".into()), " & = 11");
-    assert_eq!(pretty_eval(" & 11".into()), " & 11");
-    assert_eq!(pretty_eval(" & 11 \\".into()), " & 11 \\");
+    assert_eq!(pretty_eval(" = 11".into()).unwrap(), " = 11");
+    assert_eq!(pretty_eval(" &= 11".into()).unwrap(), " & = 11");
+    assert_eq!(pretty_eval(" & 11".into()).unwrap(), " & 11");
+    assert_eq!(pretty_eval(" & 11 \\".into()).unwrap(), " & 11 \\");
 }
 
 pub fn get_significant_digits(n: &Float) -> usize {

src/main.rs

@@ -1,12 +1,13 @@
 use std::{
     env,
     io::{self, Read},
+    process::ExitCode,
 };
 
 mod formatting;
 mod nodes;
 
-fn main() {
+fn main() -> ExitCode {
     let input = match env::args().skip(1).rev().reduce(|x, a| a + &x) {
         Some(s) => s,
         None => {
@@ -16,5 +17,14 @@ fn main() {
         }
     };
 
-    println!("{}", formatting::pretty_eval(input));
+    match formatting::pretty_eval(input) {
+        Ok(s) => println!("{s}"),
+
+        Err(e) => {
+            eprintln!("{e}");
+            return ExitCode::FAILURE;
+        }
+    }
+
+    ExitCode::SUCCESS
 }

src/nodes/evaluate.rs

@@ -5,25 +5,35 @@ use rug::{
 
 use crate::nodes::{Function, Node, Nodes, Operator};
 
+#[derive(Clone, Debug, thiserror::Error)]
+pub enum Error {
+    #[error("invalid operand: {0}")]
+    InvalidOperand(Node),
+    #[error("missing argument, got: {0}")]
+    MissingArgument(Node),
+    #[error("collapse failed, left with: {0}")]
+    CollapseFailed(Nodes),
+}
+
 impl Nodes {
     /// Consume the `Nodes`, collapsing them down to a single number
-    pub fn evaluate(mut self) -> Float {
+    pub fn evaluate(mut self) -> Result<Float, Error> {
         let nodes = &mut self.0;
 
         while let Some(end) = nodes.iter().position(|n| *n == Node::ParenthesisEnd) {
-            collapse_toplevel(nodes, end);
+            collapse_toplevel(nodes, end)?;
         }
         let len = nodes.len();
-        collapse_toplevel(nodes, len);
+        collapse_toplevel(nodes, len)?;
 
         match nodes.pop().unwrap() {
-            Node::Number(n) => n,
-            _ => panic!("failed to collapse nodes: {nodes:?}"),
+            Node::Number(n) => Ok(n),
+            _ => Err(Error::CollapseFailed(self)),
         }
     }
 }
 
-fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) {
+fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) -> Result<(), Error> {
     let start = nodes[0..end]
         .iter()
         .rposition(|n| *n == Node::ParenthesisStart)
@@ -51,7 +61,7 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) {
                 Function::Secant => n.sec_mut(),
                 Function::CoSecant => n.csc_mut(),
             },
-            n => panic!("function is missing an argument, got: {n:?}"),
+            n => return Err(Error::MissingArgument(n.clone())),
         };
 
         nodes.remove(start + index);
@@ -64,12 +74,12 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) {
     {
         let lhs = match nodes.remove(start + operator - 1) {
             Node::Number(n) => n,
-            n => panic!("operator has an invalid operand: {n:?}"),
+            n => return Err(Error::InvalidOperand(n)),
         };
         end -= 1;
         match &mut nodes[start..end][operator] {
             Node::Number(n) => n.pow_from(lhs),
-            n => panic!("operator has an invalid operand: {n:?}"),
+            n => return Err(Error::InvalidOperand(n.clone())),
         };
 
         nodes.remove(start + operator - 1);
@@ -82,12 +92,12 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) {
     {
         let lhs = match nodes.remove(start + operator - 1) {
             Node::Number(n) => n,
-            n => panic!("operator has an invalid operand: {n:?}"),
+            n => return Err(Error::InvalidOperand(n)),
         };
         end -= 1;
         match &mut nodes[start..end][operator] {
             Node::Number(n) => n.div_from(lhs),
-            n => panic!("operator has an invalid operand: {n:?}"),
+            n => return Err(Error::InvalidOperand(n.clone())),
         };
 
         nodes.remove(start + operator - 1);
@@ -100,12 +110,12 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) {
     {
         let lhs = match nodes.remove(start + operator - 1) {
             Node::Number(n) => n,
-            n => panic!("operator has an invalid operand: {n:?}"),
+            n => return Err(Error::InvalidOperand(n)),
         };
         end -= 1;
         match &mut nodes[start..end][operator] {
             Node::Number(n) => n.mul_from(lhs),
-            n => panic!("operator has an invalid operand: {n:?}"),
+            n => return Err(Error::InvalidOperand(n.clone())),
         };
 
         nodes.remove(start + operator - 1);
@@ -118,12 +128,12 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) {
     {
         let lhs = match nodes.remove(start + operator - 1) {
             Node::Number(n) => n,
-            n => panic!("operator has an invalid operand: {n:?}"),
+            n => return Err(Error::InvalidOperand(n)),
         };
         end -= 1;
         match &mut nodes[start..end][operator] {
             Node::Number(n) => n.sub_from(lhs),
-            n => panic!("operator has an invalid operand: {n:?}"),
+            n => return Err(Error::InvalidOperand(n.clone())),
         };
 
         nodes.remove(start + operator - 1);
@@ -136,12 +146,12 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) {
     {
         let lhs = match nodes.remove(start + operator - 1) {
             Node::Number(n) => n,
-            n => panic!("operator has an invalid operand: {n:?}"),
+            n => return Err(Error::InvalidOperand(n)),
         };
         end -= 1;
         match &mut nodes[start..end][operator] {
             Node::Number(n) => n.add_from(lhs),
-            n => panic!("operator has an invalid operand: {n:?}"),
+            n => return Err(Error::InvalidOperand(n.clone())),
         };
 
         nodes.remove(start + operator - 1);
@@ -152,6 +162,8 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) {
         nodes.remove(end);
         nodes.remove(start);
     }
+
+    Ok(())
 }
 
 #[cfg(test)]
@@ -169,6 +181,7 @@ fn test() {
             Node::Number(Float::with_val(PREC, 1))
         ])
         .evaluate()
+        .unwrap()
         .to_f64(),
         1.9092974268256817,
     );

src/nodes/mod.rs

@@ -2,6 +2,8 @@
 //! as well as the logic to parse it from a string (`Node::from_str`),
 //! and the logic to evaluate it into a single number (`Node::evaluate`).
 
+use std::fmt::{Debug, Display};
+
 use rug::Float;
 
 mod evaluate;
@@ -9,10 +11,18 @@ pub mod from_str;
 #[cfg(test)]
 mod tests;
 
+#[derive(Clone, Debug, thiserror::Error)]
+pub enum Error {
+    #[error("{0}")]
+    Parsing(#[from] from_str::Error),
+    #[error("{0}")]
+    Evaluation(#[from] evaluate::Error),
+}
+
 /// helper function to parse to Nodes and immediately evaluate
-pub fn eval(s: &str) -> Result<rug::Float, from_str::Error> {
+pub fn eval(s: &str) -> Result<rug::Float, Error> {
     use std::str::FromStr;
-    Nodes::from_str(s).map(|nodes| nodes.evaluate())
+    Ok(Nodes::from_str(s)?.evaluate()?)
 }
 
 pub const PREC: u32 = 512;
@@ -24,18 +34,28 @@ impl AsRef<[Node]> for Nodes {
         self.0.as_ref()
     }
 }
+impl Display for Nodes {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        Debug::fmt(&self.0, f)
+    }
+}
 
 #[derive(Debug, Clone, PartialEq)]
-enum Node {
+pub enum Node {
     Function(Function),
     ParenthesisStart,
     ParenthesisEnd,
     Number(Float),
     Operator(Operator),
 }
+impl Display for Node {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        Debug::fmt(&self, f)
+    }
+}
 
 #[derive(Debug, Default, Copy, Clone, PartialEq)]
-enum Operator {
+pub enum Operator {
     Plus,
     Minus,
     #[default]
@@ -45,7 +65,7 @@ enum Operator {
 }
 
 #[derive(Debug, Copy, Clone, PartialEq)]
-enum Function {
+pub enum Function {
     Sqrt,
 
     Sine,

src/nodes/tests.rs

@@ -4,7 +4,7 @@ use std::str::FromStr;
 use crate::nodes::Nodes;
 
 fn eval(s: &str) -> f64 {
-    Nodes::from_str(s).unwrap().evaluate().to_f64()
+    Nodes::from_str(s).unwrap().evaluate().unwrap().to_f64()
 }
 
 #[test]