Fix Unit::expression_reduced()

crates/api/CHANGELOG.md

@@ -16,6 +16,8 @@ adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 - Added `assert_field_eq!()` macro to allow checking exact equality of objects (since current
   implementation of `PartialEq` does not do this).
 - `Composition` now derives `Ord`.
+- `Unit::simplify()`, extracted from the (redesigned) innards of `Unit::expression_reduced()`.
+- `Term` now derives `Hash`.
 
 ### Changed
 

crates/api/src/annotation.rs

@@ -9,7 +9,7 @@ use crate::{
     Composable, IsCompatibleWith, Term,
 };
 
-#[derive(Default, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
+#[derive(Default, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct Annotation(String);
 
 impl Annotation {

crates/api/src/term.rs

@@ -62,7 +62,7 @@ impl From<Atom> for Term {
 ///   `1+2{foo}`; raised to the -2nd power becomes `1-2{foo}`. Notice that a factor, exponent and
 ///   annotation are all required to represent that.
 ///
-#[derive(Clone, Debug, Eq)]
+#[derive(Clone, Debug, Eq, Hash)]
 pub enum Term {
     /// Ex. "{tree}", where the inner `String` would be the contents inside the curly braces.
     ///

crates/api/src/term/term_reduce.rs

@@ -15,7 +15,7 @@ pub(crate) trait TermReduce: crate::composable::ComposablyEq<Term> {
     fn term_reduce(&self, rhs: &Term) -> ReducedTerm {
         match self.composably_eq(rhs) {
             Some(0) => ReducedTerm::ReducedAway,
-            Some(exponent) => ReducedTerm::ReducedToTerm(self.build(exponent).into()),
+            Some(exponent) => ReducedTerm::ReducedToTerm(self.build(exponent)),
             None => ReducedTerm::NotReducible,
         }
     }

crates/api/src/term/variants/atom_annotation.rs

@@ -17,7 +17,7 @@ use super::{
 // ╰────────────────╯
 /// Ex. "g{sucrose}"
 ///
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct AtomAnnotation {
     pub(crate) atom: Atom,
     pub(crate) annotation: Annotation,

crates/api/src/term/variants/atom_exponent.rs

@@ -17,7 +17,7 @@ use super::{
 // ╰──────────────╯
 /// Ex. "m2"
 ///
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub struct AtomExponent {
     pub(crate) atom: Atom,
     pub(crate) exponent: Exponent,

crates/api/src/term/variants/atom_exponent_annotation.rs

@@ -17,7 +17,7 @@ use super::{
 // ╰────────────────────────╯
 /// Ex. "m2{peaches}"
 ///
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct AtomExponentAnnotation {
     pub(crate) atom: Atom,
     pub(crate) exponent: Exponent,

crates/api/src/term/variants/factor_annotation.rs

@@ -14,7 +14,7 @@ use super::{
 // ╭──────────────────╮
 // │ FactorAnnotation │
 // ╰──────────────────╯
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct FactorAnnotation {
     pub(crate) factor: Factor,
     pub(crate) annotation: Annotation,

crates/api/src/term/variants/factor_atom.rs

@@ -15,7 +15,7 @@ use super::{
 // ╭────────────╮
 // │ FactorAtom │
 // ╰────────────╯
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub struct FactorAtom {
     pub(crate) factor: Factor,
     pub(crate) atom: Atom,

crates/api/src/term/variants/factor_atom_annotation.rs

@@ -15,7 +15,7 @@ use super::{
 // ╭──────────────────────╮
 // │ FactorAtomAnnotation │
 // ╰──────────────────────╯
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct FactorAtomAnnotation {
     pub(crate) factor: Factor,
     pub(crate) atom: Atom,

crates/api/src/term/variants/factor_atom_exponent.rs

@@ -15,7 +15,7 @@ use super::{
 // ╭────────────────────╮
 // │ FactorAtomExponent │
 // ╰────────────────────╯
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub struct FactorAtomExponent {
     pub(crate) factor: Factor,
     pub(crate) atom: Atom,

crates/api/src/term/variants/factor_atom_exponent_annotation.rs

@@ -15,7 +15,7 @@ use super::{
 // ╭──────────────────────────────╮
 // │ FactorAtomExponentAnnotation │
 // ╰──────────────────────────────╯
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct FactorAtomExponentAnnotation {
     pub(crate) factor: Factor,
     pub(crate) atom: Atom,

crates/api/src/term/variants/factor_exponent.rs

@@ -15,7 +15,7 @@ use super::{
 // ╭────────────────╮
 // │ FactorExponent │
 // ╰────────────────╯
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub struct FactorExponent {
     pub(crate) factor: Factor,
     pub(crate) exponent: Exponent,

crates/api/src/term/variants/factor_exponent_annotation.rs

@@ -14,7 +14,7 @@ use super::{
 // ╭──────────────────────────╮
 // │ FactorExponentAnnotation │
 // ╰──────────────────────────╯
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct FactorExponentAnnotation {
     pub(crate) factor: Factor,
     pub(crate) exponent: Exponent,

crates/api/src/term/variants/factor_prefix_atom.rs

@@ -15,7 +15,7 @@ use super::{
 // ╭──────────────────╮
 // │ FactorPrefixAtom │
 // ╰──────────────────╯
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub struct FactorPrefixAtom {
     pub(crate) factor: Factor,
     pub(crate) prefix: Prefix,

crates/api/src/term/variants/factor_prefix_atom_annotation.rs

@@ -15,7 +15,7 @@ use super::{
 // ╭────────────────────────────╮
 // │ FactorPrefixAtomAnnotation │
 // ╰────────────────────────────╯
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct FactorPrefixAtomAnnotation {
     pub(crate) factor: Factor,
     pub(crate) prefix: Prefix,

crates/api/src/term/variants/factor_prefix_atom_exponent.rs

@@ -15,7 +15,7 @@ use super::{
 // ╭──────────────────────────╮
 // │ FactorPrefixAtomExponent │
 // ╰──────────────────────────╯
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub struct FactorPrefixAtomExponent {
     pub(crate) factor: Factor,
     pub(crate) prefix: Prefix,

crates/api/src/term/variants/factor_prefix_atom_exponent_annotation.rs

@@ -15,7 +15,7 @@ use super::{
 // ╭────────────────────────────────────╮
 // │ FactorPrefixAtomExponentAnnotation │
 // ╰────────────────────────────────────╯
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct FactorPrefixAtomExponentAnnotation {
     pub(crate) factor: Factor,
     pub(crate) prefix: Prefix,

crates/api/src/term/variants/prefix_atom.rs

@@ -15,7 +15,7 @@ use super::{
 // ╭────────────╮
 // │ PrefixAtom │
 // ╰────────────╯
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub struct PrefixAtom {
     pub(crate) prefix: Prefix,
     pub(crate) atom: Atom,

crates/api/src/term/variants/prefix_atom_annotation.rs

@@ -16,7 +16,7 @@ use super::{
 // ╭──────────────────────╮
 // │ PrefixAtomAnnotation │
 // ╰──────────────────────╯
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct PrefixAtomAnnotation {
     pub(crate) prefix: Prefix,
     pub(crate) atom: Atom,

crates/api/src/term/variants/prefix_atom_exponent.rs

@@ -15,7 +15,7 @@ use super::{
 // ╭────────────────────╮
 // │ PrefixAtomExponent │
 // ╰────────────────────╯
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub struct PrefixAtomExponent {
     pub(crate) prefix: Prefix,
     pub(crate) atom: Atom,

crates/api/src/term/variants/prefix_atom_exponent_annotation.rs

@@ -16,7 +16,7 @@ use super::{
 // ╭──────────────────────────────╮
 // │ PrefixAtomExponentAnnotation │
 // ╰──────────────────────────────╯
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct PrefixAtomExponentAnnotation {
     pub(crate) prefix: Prefix,
     pub(crate) atom: Atom,

crates/api/src/unit.rs

@@ -146,6 +146,48 @@ impl Unit {
         self.to_string()
     }
 
+    /// If the unit terms are a fraction and can be reduced, this returns a new
+    /// `Unit` with those terms. Ex. terms that would normally render
+    /// `[acr_us].[in_i]/[acr_us]` would simply render `[in_i]`.
+    ///
+    /// ```rust
+    /// use wise_units::{Unit, parse_unit};
+    ///
+    /// let u = parse_unit!("[acr_us].[in_i]/[acr_us]");
+    /// assert_eq!(u.simplify(), parse_unit!("[in_i]"));
+    /// ```
+    ///
+    #[must_use]
+    pub fn simplify(&self) -> Self {
+        fn reduce_head_tail(remaining_terms: &[Term]) -> Option<(Term, term_reducing::WhatToKeep)> {
+            if let Some((head, tail)) = remaining_terms.split_first() {
+                Some((
+                    head.clone(),
+                    term_reducing::simplify_one_to_many(head, tail),
+                ))
+            } else {
+                None
+            }
+        }
+
+        let mut output: Vec<Term> = Vec::new();
+
+        if let Some((lhs, what_to_keep)) = reduce_head_tail(&self.terms) {
+            if what_to_keep.keep_lhs {
+                output.push(lhs);
+            }
+
+            output.extend(what_to_keep.new_terms);
+
+            Self::new(term_reducing::compare_and_cancel(
+                &output,
+                what_to_keep.kept_terms,
+            ))
+        } else {
+            self.clone()
+        }
+    }
+
     /// If the unit terms are a fraction and can be reduced, this returns those
     /// as a string. Ex. terms that would normally render
     /// `[acr_us].[in_i]/[acr_us]` would simply render `[in_i]`.
@@ -161,9 +203,7 @@ impl Unit {
     #[inline]
     #[must_use]
     pub fn expression_reduced(&self) -> String {
-        let reduced = term_reducing::reduce_terms(&self.terms);
-
-        Self::new(reduced).to_string()
+        self.simplify().to_string()
     }
 
     pub fn numerator_terms(&self) -> impl Iterator<Item = &Term> {
@@ -232,6 +272,7 @@ mod tests {
     #[test]
     fn validate_expression_reduced() {
         assert_eq!(METER.expression_reduced(), "m");
+        assert_eq!(UNITY.expression_reduced(), "1");
         assert_eq!(parse_unit!("M").expression_reduced(), "m");
         assert_eq!(parse_unit!("km/10m").expression_reduced(), "km/10m");
         assert_eq!(parse_unit!("m-1").expression_reduced(), "/m");
@@ -248,6 +289,25 @@ mod tests {
         assert_eq!(parse_unit!("MiBy").expression_reduced(), "MiBy");
         assert_eq!(parse_unit!("GiBy").expression_reduced(), "GiBy");
         assert_eq!(parse_unit!("TiBy").expression_reduced(), "TiBy");
+
+        assert_eq!(parse_unit!("42km3{foo}").expression_reduced(), "42km3{foo}");
+        assert_eq!(
+            parse_unit!("42km3{foo}.42kg2{bar}").expression_reduced(),
+            "42km3{foo}.42kg2{bar}"
+        );
+        assert_eq!(
+            parse_unit!("42km3{foo}/42km2{foo}").expression_reduced(),
+            "42km{foo}"
+        );
+        assert_eq!(parse_unit!("km3.km/km2").expression_reduced(), "km2");
+        assert_eq!(
+            parse_unit!("{meow}/m2.g/{meow}").expression_reduced(),
+            "1+2{meow}/m2.g"
+        );
+        assert_eq!(
+            parse_unit!("{meow}/m2/g/{meow}").expression_reduced(),
+            "g/m2"
+        );
     }
 
     #[cfg(feature = "cffi")]

crates/api/src/unit/ops.rs

@@ -18,7 +18,7 @@ impl Div for Unit {
 
     #[inline]
     fn div(self, other: Self) -> Self::Output {
-        Self::new(term_reducing::meow(
+        Self::new(term_reducing::compare_and_cancel(
             &self.terms,
             other.terms.iter().map(Inv::inv).collect(),
         ))
@@ -33,9 +33,9 @@ impl<'a> Div<&'a Self> for Unit {
 
     #[inline]
     fn div(self, other: &'a Self) -> Self::Output {
-        Self::new(term_reducing::meow(
+        Self::new(term_reducing::compare_and_cancel(
             &self.terms,
-            other.terms.into_iter().map(Inv::inv).collect(),
+            other.terms.iter().map(Inv::inv).collect(),
         ))
     }
 }
@@ -48,9 +48,9 @@ impl<'a> Div for &'a Unit {
 
     #[inline]
     fn div(self, other: &'a Unit) -> Self::Output {
-        Unit::new(term_reducing::meow(
+        Unit::new(term_reducing::compare_and_cancel(
             &self.terms,
-            other.terms.into_iter().map(Inv::inv).collect(),
+            other.terms.iter().map(Inv::inv).collect(),
         ))
     }
 }
@@ -63,9 +63,9 @@ impl<'a> Div<Unit> for &'a Unit {
 
     #[inline]
     fn div(self, other: Unit) -> Self::Output {
-        Unit::new(term_reducing::meow(
+        Unit::new(term_reducing::compare_and_cancel(
             &self.terms,
-            other.terms.into_iter().map(Inv::inv).collect(),
+            other.terms.iter().map(Inv::inv).collect(),
         ))
     }
 }
@@ -81,7 +81,10 @@ impl Mul for Unit {
 
     #[inline]
     fn mul(self, other: Self) -> Self::Output {
-        Self::new(term_reducing::meow(&self.terms, other.terms.to_vec()))
+        Self::new(term_reducing::compare_and_cancel(
+            &self.terms,
+            other.terms.to_vec(),
+        ))
     }
 }
 
@@ -93,7 +96,10 @@ impl<'a> Mul<&'a Self> for Unit {
 
     #[inline]
     fn mul(self, other: &'a Self) -> Self::Output {
-        Self::new(term_reducing::meow(&self.terms, other.terms.to_vec()))
+        Self::new(term_reducing::compare_and_cancel(
+            &self.terms,
+            other.terms.to_vec(),
+        ))
     }
 }
 
@@ -105,7 +111,10 @@ impl<'a> Mul for &'a Unit {
 
     #[inline]
     fn mul(self, other: &'a Unit) -> Self::Output {
-        Unit::new(term_reducing::meow(&self.terms, other.terms.to_vec()))
+        Unit::new(term_reducing::compare_and_cancel(
+            &self.terms,
+            other.terms.to_vec(),
+        ))
     }
 }
 
@@ -117,7 +126,10 @@ impl<'a> Mul<Unit> for &'a Unit {
 
     #[inline]
     fn mul(self, other: Unit) -> Self::Output {
-        Unit::new(term_reducing::meow(&self.terms, other.terms.to_vec()))
+        Unit::new(term_reducing::compare_and_cancel(
+            &self.terms,
+            other.terms.to_vec(),
+        ))
     }
 }
 
@@ -185,7 +197,7 @@ mod tests {
         test_div!(test_factor_atom_div_factor_same_atom:
             parse_unit!("10m"), parse_unit!("20m") => parse_unit!("10m/20m"));
         test_div!(test_nondim_div_same_nondim:
-            seed(), seed() => parse_unit!("{seed}"));
+            seed(), seed() => UNITY);
         test_div!(test_unity_div_same_nondim:
             UNITY, seed() => Unit::new(vec![term!(factor: 1, exponent: -1, annotation: "seed")]));
         test_div!(test_nondim_div_atom: