Merge release 1.0.0 into stable branchHEADstable

See the tag 'v1.0.0' or the changelog for more information about this
release.

1 files changed, 419 insertions, 416 deletions

diff --git a/src/main/java/sevenUnits/unit/UnitDatabase.java b/src/main/java/sevenUnits/unit/UnitDatabase.java
index 0120067..36c225f 100644
--- a/src/main/java/sevenUnits/unit/UnitDatabase.java
+++ b/src/main/java/sevenUnits/unit/UnitDatabase.java
@@ -1,5 +1,5 @@
 /**
- * Copyright (C) 2018-2024 Adrien Hopkins
+ * Copyright (C) 2018-2025 Adrien Hopkins
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as published by
@@ -40,11 +40,9 @@ import java.util.Set;
 import java.util.function.BiFunction;
 import java.util.function.Function;
 import java.util.function.Predicate;
-import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
 import sevenUnits.utils.ConditionalExistenceCollections;
-import sevenUnits.utils.DecimalComparison;
 import sevenUnits.utils.ExpressionParser;
 import sevenUnits.utils.NameSymbol;
 import sevenUnits.utils.ObjectProduct;
@@ -52,7 +50,7 @@ import sevenUnits.utils.UncertainDouble;
 
 /**
  * A database of units, prefixes and dimensions, and their names.
- * 
+ *
  * @author Adrien Hopkins
  * @since 2019-01-07
  * @since v0.1.0
@@ -89,7 +87,7 @@ public final class UnitDatabase {
 	 * Because of ambiguities between prefixes (i.e. kilokilo = mega),
 	 * {@link #containsValue} and {@link #values()} currently ignore prefixes.
 	 * </p>
-	 * 
+	 *
 	 * @author Adrien Hopkins
 	 * @since 2019-04-13
 	 * @since v0.2.0
@@ -97,7 +95,7 @@ public final class UnitDatabase {
 	private static final class PrefixedUnitMap implements Map<String, Unit> {
 		/**
 		 * The class used for entry sets.
-		 * 
+		 *
 		 * <p>
 		 * If the map that created this set is infinite in size (has at least one
 		 * unit and at least one prefix), this set is infinite as well. If this
@@ -105,7 +103,7 @@ public final class UnitDatabase {
 		 * {@code IllegalStateException} instead of creating an infinite-sized
 		 * array.
 		 * </p>
-		 * 
+		 *
 		 * @author Adrien Hopkins
 		 * @since 2019-04-13
 		 * @since v0.2.0
@@ -114,7 +112,7 @@ public final class UnitDatabase {
 				extends AbstractSet<Map.Entry<String, Unit>> {
 			/**
 			 * The entry for this set.
-			 * 
+			 *
 			 * @author Adrien Hopkins
 			 * @since 2019-04-14
 			 * @since v0.2.0
@@ -126,7 +124,7 @@ public final class UnitDatabase {
 
 				/**
 				 * Creates the {@code PrefixedUnitEntry}.
-				 * 
+				 *
 				 * @param key   key
 				 * @param value value
 				 * @since 2019-04-14
@@ -139,6 +137,7 @@ public final class UnitDatabase {
 
 				/**
 				 * @since 2019-05-03
+				 * @since v0.3.0
 				 */
 				@Override
 				public boolean equals(final Object o) {
@@ -161,6 +160,7 @@ public final class UnitDatabase {
 
 				/**
 				 * @since 2019-05-03
+				 * @since v0.3.0
 				 */
 				@Override
 				public int hashCode() {
@@ -180,8 +180,9 @@ public final class UnitDatabase {
 				 * string is the string representation of the key, then the equals
 				 * ({@code =}) character, then the string representation of the
 				 * value.
-				 * 
+				 *
 				 * @since 2019-05-03
+				 * @since v0.3.0
 				 */
 				@Override
 				public String toString() {
@@ -192,7 +193,7 @@ public final class UnitDatabase {
 			/**
 			 * An iterator that iterates over the units of a
 			 * {@code PrefixedUnitNameSet}.
-			 * 
+			 *
 			 * @author Adrien Hopkins
 			 * @since 2019-04-14
 			 * @since v0.2.0
@@ -212,7 +213,9 @@ public final class UnitDatabase {
 				/**
 				 * Creates the
 				 * {@code UnitsDatabase.PrefixedUnitMap.PrefixedUnitNameSet.PrefixedUnitNameIterator}.
-				 * 
+				 *
+				 * @param map map to base iterator on
+				 *
 				 * @since 2019-04-14
 				 * @since v0.2.0
 				 */
@@ -228,7 +231,7 @@ public final class UnitDatabase {
 				 * @since v0.2.0
 				 */
 				private String getCurrentUnitName() {
-					final StringBuilder unitName = new StringBuilder();
+					final var unitName = new StringBuilder();
 					for (final int i : this.prefixCoordinates) {
 						unitName.append(this.prefixNames.get(i));
 					}
@@ -241,18 +244,15 @@ public final class UnitDatabase {
 				public boolean hasNext() {
 					if (this.unitNames.isEmpty())
 						return false;
-					else {
-						if (this.prefixNames.isEmpty())
-							return this.prefixCoordinates.isEmpty()
-									&& this.unitNamePosition < this.unitNames.size();
-						else
-							return true;
-					}
+					if (this.prefixNames.isEmpty())
+						return this.prefixCoordinates.isEmpty()
+								&& this.unitNamePosition < this.unitNames.size();
+					return true;
 				}
 
 				/**
 				 * Changes this iterator's position to the next available one.
-				 * 
+				 *
 				 * @since 2019-04-14
 				 * @since v0.2.0
 				 */
@@ -268,7 +268,7 @@ public final class UnitDatabase {
 							this.prefixCoordinates.add(0, 0);
 						} else {
 							// get the prefix coordinate to increment, then increment
-							int i = this.prefixCoordinates.size() - 1;
+							var i = this.prefixCoordinates.size() - 1;
 							this.prefixCoordinates.set(i,
 									this.prefixCoordinates.get(i) + 1);
 
@@ -294,7 +294,7 @@ public final class UnitDatabase {
 				@Override
 				public Entry<String, Unit> next() {
 					// get next element
-					final Entry<String, Unit> nextEntry = this.peek();
+					final var nextEntry = this.peek();
 
 					// iterate to next position
 					this.incrementPosition();
@@ -306,6 +306,7 @@ public final class UnitDatabase {
 				 * @return the next element in the iterator, without iterating over
 				 *         it
 				 * @since 2019-05-03
+				 * @since v0.3.0
 				 */
 				private Entry<String, Unit> peek() {
 					if (!this.hasNext())
@@ -322,7 +323,7 @@ public final class UnitDatabase {
 						}
 					}
 
-					final String nextName = this.getCurrentUnitName();
+					final var nextName = this.getCurrentUnitName();
 
 					return new PrefixedUnitEntry(nextName, this.map.get(nextName));
 				}
@@ -330,8 +331,9 @@ public final class UnitDatabase {
 				/**
 				 * Returns a string representation of the object. The exact details
 				 * of the representation are unspecified and subject to change.
-				 * 
+				 *
 				 * @since 2019-05-03
+				 * @since v0.3.0
 				 */
 				@Override
 				public String toString() {
@@ -346,7 +348,7 @@ public final class UnitDatabase {
 
 			/**
 			 * Creates the {@code PrefixedUnitNameSet}.
-			 * 
+			 *
 			 * @param map map that created this set
 			 * @since 2019-04-13
 			 * @since v0.2.0
@@ -383,7 +385,7 @@ public final class UnitDatabase {
 					// This is OK because I'm in a try-catch block, catching the
 					// exact exception that would be thrown.
 					@SuppressWarnings("unchecked")
-					final Entry<String, Unit> tempEntry = (Entry<String, Unit>) o;
+					final var tempEntry = (Entry<String, Unit>) o;
 					entry = tempEntry;
 				} catch (final ClassCastException e) {
 					throw new IllegalArgumentException(
@@ -441,55 +443,45 @@ public final class UnitDatabase {
 			public int size() {
 				if (this.map.units.isEmpty())
 					return 0;
-				else {
-					if (this.map.prefixes.isEmpty())
-						return this.map.units.size();
-					else
-						// infinite set
-						return Integer.MAX_VALUE;
-				}
+				if (this.map.prefixes.isEmpty())
+					return this.map.units.size();
+				// infinite set
+				return Integer.MAX_VALUE;
 			}
 
-			/**
-			 * @throws IllegalStateException if the set is infinite in size
-			 */
+			/** @throws IllegalStateException if the set is infinite in size */
 			@Override
 			public Object[] toArray() {
 				if (this.map.units.isEmpty() || this.map.prefixes.isEmpty())
 					return super.toArray();
-				else
-					// infinite set
-					throw new IllegalStateException(
-							"Cannot make an infinite set into an array.");
+				// infinite set
+				throw new IllegalStateException(
+						"Cannot make an infinite set into an array.");
 			}
 
-			/**
-			 * @throws IllegalStateException if the set is infinite in size
-			 */
+			/** @throws IllegalStateException if the set is infinite in size */
 			@Override
 			public <T> T[] toArray(final T[] a) {
 				if (this.map.units.isEmpty() || this.map.prefixes.isEmpty())
 					return super.toArray(a);
-				else
-					// infinite set
-					throw new IllegalStateException(
-							"Cannot make an infinite set into an array.");
+				// infinite set
+				throw new IllegalStateException(
+						"Cannot make an infinite set into an array.");
 			}
 
 			@Override
 			public String toString() {
 				if (this.map.units.isEmpty() || this.map.prefixes.isEmpty())
 					return super.toString();
-				else
-					return String.format(
-							"Infinite set of name-unit entries created from units %s and prefixes %s",
-							this.map.units, this.map.prefixes);
+				return String.format(
+						"Infinite set of name-unit entries created from units %s and prefixes %s",
+						this.map.units, this.map.prefixes);
 			}
 		}
 
 		/**
 		 * The class used for unit name sets.
-		 * 
+		 *
 		 * <p>
 		 * If the map that created this set is infinite in size (has at least one
 		 * unit and at least one prefix), this set is infinite as well. If this
@@ -497,7 +489,7 @@ public final class UnitDatabase {
 		 * {@code IllegalStateException} instead of creating an infinite-sized
 		 * array.
 		 * </p>
-		 * 
+		 *
 		 * @author Adrien Hopkins
 		 * @since 2019-04-13
 		 * @since v0.2.0
@@ -507,7 +499,7 @@ public final class UnitDatabase {
 			/**
 			 * An iterator that iterates over the units of a
 			 * {@code PrefixedUnitNameSet}.
-			 * 
+			 *
 			 * @author Adrien Hopkins
 			 * @since 2019-04-14
 			 * @since v0.2.0
@@ -527,7 +519,9 @@ public final class UnitDatabase {
 				/**
 				 * Creates the
 				 * {@code UnitsDatabase.PrefixedUnitMap.PrefixedUnitNameSet.PrefixedUnitNameIterator}.
-				 * 
+				 *
+				 * @param map map to base itorator on
+				 *
 				 * @since 2019-04-14
 				 * @since v0.2.0
 				 */
@@ -543,7 +537,7 @@ public final class UnitDatabase {
 				 * @since v0.2.0
 				 */
 				private String getCurrentUnitName() {
-					final StringBuilder unitName = new StringBuilder();
+					final var unitName = new StringBuilder();
 					for (final int i : this.prefixCoordinates) {
 						unitName.append(this.prefixNames.get(i));
 					}
@@ -556,18 +550,15 @@ public final class UnitDatabase {
 				public boolean hasNext() {
 					if (this.unitNames.isEmpty())
 						return false;
-					else {
-						if (this.prefixNames.isEmpty())
-							return this.prefixCoordinates.isEmpty()
-									&& this.unitNamePosition < this.unitNames.size();
-						else
-							return true;
-					}
+					if (this.prefixNames.isEmpty())
+						return this.prefixCoordinates.isEmpty()
+								&& this.unitNamePosition < this.unitNames.size();
+					return true;
 				}
 
 				/**
 				 * Changes this iterator's position to the next available one.
-				 * 
+				 *
 				 * @since 2019-04-14
 				 * @since v0.2.0
 				 */
@@ -583,7 +574,7 @@ public final class UnitDatabase {
 							this.prefixCoordinates.add(0, 0);
 						} else {
 							// get the prefix coordinate to increment, then increment
-							int i = this.prefixCoordinates.size() - 1;
+							var i = this.prefixCoordinates.size() - 1;
 							this.prefixCoordinates.set(i,
 									this.prefixCoordinates.get(i) + 1);
 
@@ -608,7 +599,7 @@ public final class UnitDatabase {
 
 				@Override
 				public String next() {
-					final String nextName = this.peek();
+					final var nextName = this.peek();
 
 					this.incrementPosition();
 
@@ -619,6 +610,7 @@ public final class UnitDatabase {
 				 * @return the next element in the iterator, without iterating over
 				 *         it
 				 * @since 2019-05-03
+				 * @since v0.3.0
 				 */
 				private String peek() {
 					if (!this.hasNext())
@@ -640,8 +632,9 @@ public final class UnitDatabase {
 				/**
 				 * Returns a string representation of the object. The exact details
 				 * of the representation are unspecified and subject to change.
-				 * 
+				 *
 				 * @since 2019-05-03
+				 * @since v0.3.0
 				 */
 				@Override
 				public String toString() {
@@ -656,7 +649,7 @@ public final class UnitDatabase {
 
 			/**
 			 * Creates the {@code PrefixedUnitNameSet}.
-			 * 
+			 *
 			 * @param map map that created this set
 			 * @since 2019-04-13
 			 * @since v0.2.0
@@ -734,56 +727,46 @@ public final class UnitDatabase {
 			public int size() {
 				if (this.map.units.isEmpty())
 					return 0;
-				else {
-					if (this.map.prefixes.isEmpty())
-						return this.map.units.size();
-					else
-						// infinite set
-						return Integer.MAX_VALUE;
-				}
+				if (this.map.prefixes.isEmpty())
+					return this.map.units.size();
+				// infinite set
+				return Integer.MAX_VALUE;
 			}
 
-			/**
-			 * @throws IllegalStateException if the set is infinite in size
-			 */
+			/** @throws IllegalStateException if the set is infinite in size */
 			@Override
 			public Object[] toArray() {
 				if (this.map.units.isEmpty() || this.map.prefixes.isEmpty())
 					return super.toArray();
-				else
-					// infinite set
-					throw new IllegalStateException(
-							"Cannot make an infinite set into an array.");
+				// infinite set
+				throw new IllegalStateException(
+						"Cannot make an infinite set into an array.");
 
 			}
 
-			/**
-			 * @throws IllegalStateException if the set is infinite in size
-			 */
+			/** @throws IllegalStateException if the set is infinite in size */
 			@Override
 			public <T> T[] toArray(final T[] a) {
 				if (this.map.units.isEmpty() || this.map.prefixes.isEmpty())
 					return super.toArray(a);
-				else
-					// infinite set
-					throw new IllegalStateException(
-							"Cannot make an infinite set into an array.");
+				// infinite set
+				throw new IllegalStateException(
+						"Cannot make an infinite set into an array.");
 			}
 
 			@Override
 			public String toString() {
 				if (this.map.units.isEmpty() || this.map.prefixes.isEmpty())
 					return super.toString();
-				else
-					return String.format(
-							"Infinite set of name-unit entries created from units %s and prefixes %s",
-							this.map.units, this.map.prefixes);
+				return String.format(
+						"Infinite set of name-unit entries created from units %s and prefixes %s",
+						this.map.units, this.map.prefixes);
 			}
 		}
 
 		/**
 		 * The units stored in this collection, without prefixes.
-		 * 
+		 *
 		 * @since 2019-04-13
 		 * @since v0.2.0
 		 */
@@ -791,7 +774,7 @@ public final class UnitDatabase {
 
 		/**
 		 * The available prefixes for use.
-		 * 
+		 *
 		 * @since 2019-04-13
 		 * @since v0.2.0
 		 */
@@ -804,7 +787,7 @@ public final class UnitDatabase {
 
 		/**
 		 * Creates the {@code PrefixedUnitMap}.
-		 * 
+		 *
 		 * @param units    map mapping unit names to units
 		 * @param prefixes map mapping prefix names to prefixes
 		 * @since 2019-04-13
@@ -855,11 +838,11 @@ public final class UnitDatabase {
 			if (!(key instanceof String))
 				throw new IllegalArgumentException(
 						"Attempted to test for a unit using a non-string name.");
-			final String unitName = (String) key;
+			final var unitName = (String) key;
 
 			// Then, look for the longest prefix that is attached to a valid unit
 			String longestPrefix = null;
-			int longestLength = 0;
+			var longestLength = 0;
 
 			for (final String prefixName : this.prefixes.keySet()) {
 				// a prefix name is valid if:
@@ -871,7 +854,7 @@ public final class UnitDatabase {
 				// linear units can have prefixes)
 				if (unitName.startsWith(prefixName)
 						&& prefixName.length() > longestLength) {
-					final String rest = unitName.substring(prefixName.length());
+					final var rest = unitName.substring(prefixName.length());
 					if (this.containsKey(rest)
 							&& this.get(rest) instanceof LinearUnit) {
 						longestPrefix = prefixName;
@@ -885,7 +868,7 @@ public final class UnitDatabase {
 
 		/**
 		 * {@inheritDoc}
-		 * 
+		 *
 		 * <p>
 		 * Because of ambiguities between prefixes (i.e. kilokilo = mega), this
 		 * method only tests for prefixless units.
@@ -914,11 +897,11 @@ public final class UnitDatabase {
 			if (!(key instanceof String))
 				throw new IllegalArgumentException(
 						"Attempted to obtain a unit using a non-string name.");
-			final String unitName = (String) key;
+			final var unitName = (String) key;
 
 			// Then, look for the longest prefix that is attached to a valid unit
 			String longestPrefix = null;
-			int longestLength = 0;
+			var longestLength = 0;
 
 			for (final String prefixName : this.prefixes.keySet()) {
 				// a prefix name is valid if:
@@ -930,7 +913,7 @@ public final class UnitDatabase {
 				// linear units can have prefixes)
 				if (unitName.startsWith(prefixName)
 						&& prefixName.length() > longestLength) {
-					final String rest = unitName.substring(prefixName.length());
+					final var rest = unitName.substring(prefixName.length());
 					if (this.containsKey(rest)
 							&& this.get(rest) instanceof LinearUnit) {
 						longestPrefix = prefixName;
@@ -942,16 +925,14 @@ public final class UnitDatabase {
 			// if none found, returns null
 			if (longestPrefix == null)
 				return null;
-			else {
-				// get necessary data
-				final String rest = unitName.substring(longestLength);
-				// this cast will not fail because I verified that it would work
-				// before selecting this prefix
-				final LinearUnit unit = (LinearUnit) this.get(rest);
-				final UnitPrefix prefix = this.prefixes.get(longestPrefix);
-
-				return unit.withPrefix(prefix);
-			}
+			// get necessary data
+			final var rest = unitName.substring(longestLength);
+			// this cast will not fail because I verified that it would work
+			// before selecting this prefix
+			final var unit = (LinearUnit) this.get(rest);
+			final var prefix = this.prefixes.get(longestPrefix);
+
+			return unit.withPrefix(prefix);
 		}
 
 		@Override
@@ -1028,28 +1009,24 @@ public final class UnitDatabase {
 		public int size() {
 			if (this.units.isEmpty())
 				return 0;
-			else {
-				if (this.prefixes.isEmpty())
-					return this.units.size();
-				else
-					// infinite set
-					return Integer.MAX_VALUE;
-			}
+			if (this.prefixes.isEmpty())
+				return this.units.size();
+			// infinite set
+			return Integer.MAX_VALUE;
 		}
 
 		@Override
 		public String toString() {
 			if (this.units.isEmpty() || this.prefixes.isEmpty())
 				return new HashMap<>(this).toString();
-			else
-				return String.format(
-						"Infinite map of name-unit entries created from units %s and prefixes %s",
-						this.units, this.prefixes);
+			return String.format(
+					"Infinite map of name-unit entries created from units %s and prefixes %s",
+					this.units, this.prefixes);
 		}
 
 		/**
 		 * {@inheritDoc}
-		 * 
+		 *
 		 * <p>
 		 * Because of ambiguities between prefixes (i.e. kilokilo = mega), this
 		 * method ignores prefixes.
@@ -1066,34 +1043,6 @@ public final class UnitDatabase {
 	}
 
 	/**
-	 * Replacements done to *all* expression types
-	 */
-	private static final Map<Pattern, String> EXPRESSION_REPLACEMENTS = new HashMap<>();
-
-	// add data to expression replacements
-	static {
-		// add spaces around operators
-		for (final String operator : Arrays.asList("\\*", "/", "\\|", "\\^")) {
-			EXPRESSION_REPLACEMENTS.put(Pattern.compile(operator),
-					" " + operator + " ");
-		}
-
-		// replace multiple spaces with a single space
-		EXPRESSION_REPLACEMENTS.put(Pattern.compile(" +"), " ");
-		// place brackets around any expression of the form "number unit", with or
-		// without the space
-		EXPRESSION_REPLACEMENTS.put(Pattern.compile("((?:-?[1-9]\\d*|0)" // integer
-				+ "(?:\\.\\d+(?:[eE]\\d+))?)" // optional decimal point with numbers
-														// after it
-				+ "\\s*" // optional space(s)
-				+ "([a-zA-Z]+(?:\\^\\d+)?" // any string of letters
-				+ "(?:\\s+[a-zA-Z]+(?:\\^\\d+)?))" // optional other letters
-				+ "(?!-?\\d)" // no number directly afterwards (avoids matching
-									// "1e3")
-		), "\\($1 $2\\)");
-	}
-
-	/**
 	 * A regular expression that separates names and expressions in unit files.
 	 */
 	private static final Pattern NAME_EXPRESSION = Pattern
@@ -1108,66 +1057,76 @@ public final class UnitDatabase {
 
 	/**
 	 * The exponent operator
-	 * 
+	 *
 	 * @param base         base of exponentiation
 	 * @param exponentUnit exponent
 	 * @return result
 	 * @since 2019-04-10
 	 * @since v0.2.0
 	 */
-	private static final LinearUnit exponentiateUnits(final LinearUnit base,
+	private static LinearUnit exponentiateUnits(final LinearUnit base,
 			final LinearUnit exponentUnit) {
-		// exponent function - first check if o2 is a number,
-		if (exponentUnit.getBase().equals(Metric.ONE.getBase())) {
-			// then check if it is an integer,
-			final double exponent = exponentUnit.getConversionFactor();
-			if (DecimalComparison.equals(exponent % 1, 0))
-				// then exponentiate
-				return base.toExponent((int) (exponent + 0.5));
-			else
-				// not an integer
-				throw new UnsupportedOperationException(
-						"Decimal exponents are currently not supported.");
-		} else
-			// not a number
-			throw new IllegalArgumentException("Exponents must be numbers.");
+		if (!exponentUnit.getBase().equals(Metric.ONE.getBase()))
+			throw new IllegalArgumentException(String.format(
+					"Tried to exponentiate %s^%s, but exponents must be dimensionless numbers.",
+					base, exponentUnit));
+
+		final var exponent = exponentUnit.getConversionFactor();
+		return base.toExponentRounded(exponent);
 	}
 
 	/**
 	 * The exponent operator
-	 * 
+	 *
 	 * @param base         base of exponentiation
 	 * @param exponentUnit exponent
 	 * @return result
 	 * @since 2020-08-04
+	 * @since v0.3.0
 	 */
-	private static final LinearUnitValue exponentiateUnitValues(
+	private static LinearUnitValue exponentiateUnitValues(
 			final LinearUnitValue base, final LinearUnitValue exponentValue) {
-		// exponent function - first check if o2 is a number,
-		if (exponentValue.canConvertTo(Metric.ONE)) {
-			// then check if it is an integer,
-			final double exponent = exponentValue.getValueExact();
-			if (DecimalComparison.equals(exponent % 1, 0))
-				// then exponentiate
-				return base.toExponent((int) (exponent + 0.5));
-			else
-				// not an integer
-				throw new UnsupportedOperationException(
-						"Decimal exponents are currently not supported.");
-		} else
-			// not a number
-			throw new IllegalArgumentException("Exponents must be numbers.");
+		if (!exponentValue.canConvertTo(Metric.ONE))
+			throw new IllegalArgumentException(String.format(
+					"Tried to exponentiate %s^%s, but exponents must be dimensionless numbers.",
+					base, exponentValue));
+
+		final var exponent = exponentValue.getValueExact();
+		return base.toExponentRounded(exponent);
+	}
+
+	/**
+	 * Formats an expression so it can be parsed by the expression parser.
+	 *
+	 * Specifically, puts spaces around all operators so they can be parsed as
+	 * words.
+	 *
+	 * @param expression expression to format
+	 * @return formatted expression
+	 * @since 2025-06-07
+	 * @since v1.0.0
+	 */
+	static String formatExpression(String expression) {
+		var modifiedExpression = expression;
+		for (final String operator : Arrays.asList("\\*", "/", "\\|", "\\^")) {
+			modifiedExpression = modifiedExpression.replaceAll(operator,
+					" " + operator + " ");
+		}
+
+		modifiedExpression = modifiedExpression.replaceAll("\\s+", " ");
+		return modifiedExpression;
 	}
 
 	/**
 	 * @return true if entry represents a removable duplicate entry of map.
 	 * @since 2021-05-22
+	 * @since v0.3.0
 	 */
 	static <T> boolean isRemovableDuplicate(Map<String, T> map,
 			Entry<String, T> entry) {
 		for (final Entry<String, T> e : map.entrySet()) {
-			final String name = e.getKey();
-			final T value = e.getValue();
+			final var name = e.getKey();
+			final var value = e.getValue();
 			if (lengthFirstComparator.compare(entry.getKey(), name) < 0
 					&& Objects.equals(map.get(entry.getKey()), value))
 				return true;
@@ -1177,7 +1136,7 @@ public final class UnitDatabase {
 
 	/**
 	 * The units in this system, excluding prefixes.
-	 * 
+	 *
 	 * @since 2019-01-07
 	 * @since v0.1.0
 	 */
@@ -1185,7 +1144,7 @@ public final class UnitDatabase {
 
 	/**
 	 * The unit prefixes in this system.
-	 * 
+	 *
 	 * @since 2019-01-14
 	 * @since v0.1.0
 	 */
@@ -1193,7 +1152,7 @@ public final class UnitDatabase {
 
 	/**
 	 * The dimensions in this system.
-	 * 
+	 *
 	 * @since 2019-03-14
 	 * @since v0.2.0
 	 */
@@ -1201,13 +1160,21 @@ public final class UnitDatabase {
 
 	/**
 	 * A map mapping strings to units (including prefixes)
-	 * 
+	 *
 	 * @since 2019-04-13
 	 * @since v0.2.0
 	 */
 	private final Map<String, Unit> units;
 
 	/**
+	 * A map mapping strings to unit sets
+	 *
+	 * @since 2024-08-16
+	 * @since v1.0.0
+	 */
+	private final Map<String, List<LinearUnit>> unitSets;
+
+	/**
 	 * The rule that specifies when prefix repetition is allowed. It takes in one
 	 * argument: a list of the prefixes being applied to the unit
 	 * <p>
@@ -1221,71 +1188,72 @@ public final class UnitDatabase {
 
 	/**
 	 * A parser that can parse unit expressions.
-	 * 
+	 *
 	 * @since 2019-03-22
 	 * @since v0.2.0
 	 */
 	private final ExpressionParser<LinearUnit> unitExpressionParser = new ExpressionParser.Builder<>(
-			this::getLinearUnit).addBinaryOperator("+", (o1, o2) -> o1.plus(o2), 0)
-			.addBinaryOperator("-", (o1, o2) -> o1.minus(o2), 0)
-			.addBinaryOperator("*", (o1, o2) -> o1.times(o2), 1)
-			.addSpaceFunction("*")
-			.addBinaryOperator("/", (o1, o2) -> o1.dividedBy(o2), 1)
-			.addBinaryOperator("|", (o1, o2) -> o1.dividedBy(o2), 3)
-			.addBinaryOperator("^", UnitDatabase::exponentiateUnits, 2).build();
+			this::getLinearUnit).addBinaryOperator("+", LinearUnit::plus, 0)
+			.addBinaryOperator("-", LinearUnit::minus, 0)
+			.addBinaryOperator("*", LinearUnit::times, 1)
+			.addBinaryOperator("space_times", LinearUnit::times, 2)
+			.addSpaceFunction("space_times")
+			.addBinaryOperator("/", LinearUnit::dividedBy, 1)
+			.addBinaryOperator("|", LinearUnit::dividedBy, 4)
+			.addBinaryOperator("^", UnitDatabase::exponentiateUnits, 3).build();
 
 	/**
 	 * A parser that can parse unit value expressions.
-	 * 
+	 *
 	 * @since 2020-08-04
+	 * @since v0.3.0
 	 */
 	private final ExpressionParser<LinearUnitValue> unitValueExpressionParser = new ExpressionParser.Builder<>(
 			this::getLinearUnitValue)
-			.addBinaryOperator("+", (o1, o2) -> o1.plus(o2), 0)
-			.addBinaryOperator("-", (o1, o2) -> o1.minus(o2), 0)
-			.addBinaryOperator("*", (o1, o2) -> o1.times(o2), 1)
-			.addSpaceFunction("*")
-			.addBinaryOperator("/", (o1, o2) -> o1.dividedBy(o2), 1)
-			.addBinaryOperator("|", (o1, o2) -> o1.dividedBy(o2), 3)
-			.addBinaryOperator("^", UnitDatabase::exponentiateUnitValues, 2)
+			.addBinaryOperator("+", LinearUnitValue::plus, 0)
+			.addBinaryOperator("-", LinearUnitValue::minus, 0)
+			.addBinaryOperator("*", LinearUnitValue::times, 1)
+			.addBinaryOperator("space_times", LinearUnitValue::times, 2)
+			.addSpaceFunction("space_times")
+			.addBinaryOperator("/", LinearUnitValue::dividedBy, 1)
+			.addBinaryOperator("|", LinearUnitValue::dividedBy, 4)
+			.addBinaryOperator("^", UnitDatabase::exponentiateUnitValues, 3)
 			.build();
 
 	/**
 	 * A parser that can parse unit prefix expressions
-	 * 
+	 *
 	 * @since 2019-04-13
 	 * @since v0.2.0
 	 */
 	private final ExpressionParser<UnitPrefix> prefixExpressionParser = new ExpressionParser.Builder<>(
-			this::getPrefix).addBinaryOperator("+", (o1, o2) -> o1.plus(o2), 0)
-			.addBinaryOperator("-", (o1, o2) -> o1.minus(o2), 0)
-			.addBinaryOperator("*", (o1, o2) -> o1.times(o2), 1)
-			.addSpaceFunction("*")
-			.addBinaryOperator("/", (o1, o2) -> o1.dividedBy(o2), 1)
-			.addBinaryOperator("|", (o1, o2) -> o1.dividedBy(o2), 3)
-			.addBinaryOperator("^", (o1, o2) -> o1.toExponent(o2.getMultiplier()),
-					2)
+			this::getPrefix).addBinaryOperator("+", UnitPrefix::plus, 0)
+			.addBinaryOperator("-", UnitPrefix::minus, 0)
+			.addBinaryOperator("*", UnitPrefix::times, 1).addSpaceFunction("*")
+			.addBinaryOperator("/", UnitPrefix::dividedBy, 1)
+			.addBinaryOperator("|", UnitPrefix::dividedBy, 3).addBinaryOperator(
+					"^", (o1, o2) -> o1.toExponent(o2.getMultiplier()), 2)
 			.build();
 
 	/**
 	 * A parser that can parse unit dimension expressions.
-	 * 
+	 *
 	 * @since 2019-04-13
 	 * @since v0.2.0
 	 */
 	private final ExpressionParser<ObjectProduct<BaseDimension>> unitDimensionParser = new ExpressionParser.Builder<>(
-			this::getDimension).addBinaryOperator("*", (o1, o2) -> o1.times(o2), 0)
+			this::getDimension).addBinaryOperator("*", ObjectProduct::times, 0)
 			.addSpaceFunction("*")
-			.addBinaryOperator("/", (o1, o2) -> o1.dividedBy(o2), 0)
-			.addBinaryOperator("|", (o1, o2) -> o1.dividedBy(o2), 2)
+			.addBinaryOperator("/", ObjectProduct::dividedBy, 0)
+			.addBinaryOperator("|", ObjectProduct::dividedBy, 2)
 			.addNumericOperator("^", (o1, o2) -> {
-				int exponent = (int) Math.round(o2.value());
+				final var exponent = (int) Math.round(o2.value());
 				return o1.toExponent(exponent);
 			}, 1).build();
 
 	/**
 	 * Creates the {@code UnitsDatabase}.
-	 * 
+	 *
 	 * @since 2019-01-10
 	 * @since v0.1.0
 	 */
@@ -1295,10 +1263,11 @@ public final class UnitDatabase {
 
 	/**
 	 * Creates the {@code UnitsDatabase}
-	 * 
+	 *
 	 * @param prefixRepetitionRule the rule that determines when prefix
 	 *                             repetition is allowed
 	 * @since 2020-08-26
+	 * @since v0.3.0
 	 */
 	public UnitDatabase(Predicate<List<UnitPrefix>> prefixRepetitionRule) {
 		this.prefixlessUnits = new HashMap<>();
@@ -1309,11 +1278,12 @@ public final class UnitDatabase {
 				new PrefixedUnitMap(this.prefixlessUnits, this.prefixes),
 				entry -> this.prefixRepetitionRule
 						.test(this.getPrefixesFromName(entry.getKey())));
+		this.unitSets = new HashMap<>();
 	}
 
 	/**
 	 * Adds a unit dimension to the database.
-	 * 
+	 *
 	 * @param name      dimension's name
 	 * @param dimension dimension to add
 	 * @throws NullPointerException if name or dimension is null
@@ -1324,14 +1294,14 @@ public final class UnitDatabase {
 			final ObjectProduct<BaseDimension> dimension) {
 		Objects.requireNonNull(name, "name may not be null");
 		Objects.requireNonNull(dimension, "dimension may not be null");
-		final ObjectProduct<BaseDimension> namedDimension = dimension
+		final var namedDimension = dimension
 				.withName(dimension.getNameSymbol().withExtraName(name));
 		this.dimensions.put(name, namedDimension);
 	}
 
 	/**
 	 * Adds to the list from a line in a unit dimension file.
-	 * 
+	 *
 	 * @param line        line to look at
 	 * @param lineCounter number of line, for error messages
 	 * @since 2019-04-10
@@ -1349,13 +1319,13 @@ public final class UnitDatabase {
 		}
 
 		// divide line into name and expression
-		final Matcher lineMatcher = NAME_EXPRESSION.matcher(line);
+		final var lineMatcher = NAME_EXPRESSION.matcher(line);
 		if (!lineMatcher.matches())
 			throw new IllegalArgumentException(String.format(
 					"Error at line %d: Lines of a dimension file must consist of a dimension name, then spaces or tabs, then a dimension expression.",
 					lineCounter));
-		final String name = lineMatcher.group(1);
-		final String expression = lineMatcher.group(2);
+		final var name = lineMatcher.group(1);
+		final var expression = lineMatcher.group(2);
 
 		// if (name.endsWith(" ")) {
 		// System.err.printf("Warning - line %d's dimension name ends in a space",
@@ -1369,22 +1339,13 @@ public final class UnitDatabase {
 				throw new IllegalArgumentException(String.format(
 						"! used but no dimension found (line %d).", lineCounter));
 		} else {
-			// it's a unit, get the unit
-			final ObjectProduct<BaseDimension> dimension;
-			try {
-				dimension = this.getDimensionFromExpression(expression);
-			} catch (final IllegalArgumentException | NoSuchElementException e) {
-				System.err.printf("Parsing error on line %d:%n", lineCounter);
-				throw e;
-			}
-
-			this.addDimension(name, dimension);
+			this.addDimension(name, this.getDimensionFromExpression(expression));
 		}
 	}
 
 	/**
 	 * Adds a unit prefix to the database.
-	 * 
+	 *
 	 * @param name   prefix's name
 	 * @param prefix prefix to add
 	 * @throws NullPointerException if name or prefix is null
@@ -1401,7 +1362,7 @@ public final class UnitDatabase {
 
 	/**
 	 * Adds a unit to the database.
-	 * 
+	 *
 	 * @param name unit's name
 	 * @param unit unit to add
 	 * @throws NullPointerException if unit is null
@@ -1418,7 +1379,7 @@ public final class UnitDatabase {
 
 	/**
 	 * Adds to the list from a line in a unit file.
-	 * 
+	 *
 	 * @param line        line to look at
 	 * @param lineCounter number of line, for error messages
 	 * @since 2019-04-10
@@ -1436,14 +1397,14 @@ public final class UnitDatabase {
 		}
 
 		// divide line into name and expression
-		final Matcher lineMatcher = NAME_EXPRESSION.matcher(line);
+		final var lineMatcher = NAME_EXPRESSION.matcher(line);
 		if (!lineMatcher.matches())
 			throw new IllegalArgumentException(String.format(
 					"Error at line %d: Lines of a unit file must consist of a unit name, then spaces or tabs, then a unit expression.",
 					lineCounter));
-		final String name = lineMatcher.group(1);
+		final var name = lineMatcher.group(1);
 
-		final String expression = lineMatcher.group(2);
+		final var expression = lineMatcher.group(2);
 
 		// this code should never occur
 		// if (name.endsWith(" ")) {
@@ -1457,47 +1418,55 @@ public final class UnitDatabase {
 			if (!this.containsUnitName(name))
 				throw new IllegalArgumentException(String
 						.format("! used but no unit found (line %d).", lineCounter));
+		} else if (name.endsWith("-")) {
+			final var prefixName = name.substring(0, name.length() - 1);
+			this.addPrefix(prefixName, this.getPrefixFromExpression(expression));
+		} else if (expression.contains(";")) {
+			// it's a multi-unit
+			this.addUnitSet(name, this.getUnitSetFromExpression(expression));
 		} else {
-			if (name.endsWith("-")) {
-				final UnitPrefix prefix;
-				try {
-					prefix = this.getPrefixFromExpression(expression);
-				} catch (final IllegalArgumentException
-						| NoSuchElementException e) {
-					System.err.printf("Parsing error on line %d:%n", lineCounter);
-					throw e;
-				}
-				final String prefixName = name.substring(0, name.length() - 1);
-				this.addPrefix(prefixName, prefix);
-			} else {
-				// it's a unit, get the unit
-				final Unit unit;
-				try {
-					unit = this.getUnitFromExpression(expression);
-				} catch (final IllegalArgumentException
-						| NoSuchElementException e) {
-					System.err.printf("Parsing error on line %d:%n", lineCounter);
-					throw e;
-				}
-				this.addUnit(name, unit);
-			}
+			// it's a unit, get the unit
+			this.addUnit(name, this.getUnitFromExpression(expression));
 		}
 	}
 
 	/**
-	 * Removes all units, prefixes and dimensions from this database.
-	 * 
+	 * Add a unit set to the database.
+	 *
+	 * @param name  name of unit set
+	 * @param value unit set to add
+	 * @since 2024-08-16
+	 * @since v1.0.0
+	 */
+	public void addUnitSet(String name, List<LinearUnit> value) {
+		if (value.isEmpty())
+			throw new IllegalArgumentException("Unit sets must not be empty.");
+		for (final LinearUnit unit : value.subList(1, value.size())) {
+			if (!Objects.equals(unit.getDimension(), value.get(0).getDimension()))
+				throw new IllegalArgumentException(
+						"Unit sets must be all the same dimension, " + value
+								+ " is not.");
+		}
+
+		this.unitSets.put(name, value);
+	}
+
+	/**
+	 * Removes all units, unit sets, prefixes and dimensions from this database.
+	 *
 	 * @since 2022-02-26
+	 * @since v0.4.0
 	 */
 	public void clear() {
 		this.dimensions.clear();
 		this.prefixes.clear();
 		this.prefixlessUnits.clear();
+		this.unitSets.clear();
 	}
 
 	/**
 	 * Tests if the database has a unit dimension with this name.
-	 * 
+	 *
 	 * @param name name to test
 	 * @return if database contains name
 	 * @since 2019-03-14
@@ -1509,7 +1478,7 @@ public final class UnitDatabase {
 
 	/**
 	 * Tests if the database has a unit prefix with this name.
-	 * 
+	 *
 	 * @param name name to test
 	 * @return if database contains name
 	 * @since 2019-01-13
@@ -1522,7 +1491,7 @@ public final class UnitDatabase {
 	/**
 	 * Tests if the database has a unit with this name, taking prefixes into
 	 * consideration
-	 * 
+	 *
 	 * @param name name to test
 	 * @return if database contains name
 	 * @since 2019-01-13
@@ -1533,6 +1502,19 @@ public final class UnitDatabase {
 	}
 
 	/**
+	 * Returns true iff there is a unit set with this name.
+	 *
+	 * @param name name to check for
+	 * @return true iff there is a unit set with this name
+	 *
+	 * @since 2024-08-16
+	 * @since v1.0.0
+	 */
+	public boolean containsUnitSetName(String name) {
+		return this.unitSets.containsKey(name);
+	}
+
+	/**
 	 * @return a map mapping dimension names to dimensions
 	 * @since 2019-04-13
 	 * @since v0.2.0
@@ -1544,10 +1526,11 @@ public final class UnitDatabase {
 	/**
 	 * Evaluates a unit expression, following the same rules as
 	 * {@link #getUnitFromExpression}.
-	 * 
+	 *
 	 * @param expression expression to parse
 	 * @return {@code LinearUnitValue} representing value of expression
 	 * @since 2020-08-04
+	 * @since v0.3.0
 	 */
 	public LinearUnitValue evaluateUnitExpression(final String expression) {
 		Objects.requireNonNull(expression, "expression must not be null.");
@@ -1556,37 +1539,13 @@ public final class UnitDatabase {
 		if (this.containsUnitName(expression))
 			return this.getLinearUnitValue(expression);
 
-		// force operators to have spaces
-		String modifiedExpression = expression;
-		modifiedExpression = modifiedExpression.replaceAll("\\+", " \\+ ");
-		modifiedExpression = modifiedExpression.replaceAll("-", " - ");
-
-		// format expression
-		for (final Entry<Pattern, String> replacement : EXPRESSION_REPLACEMENTS
-				.entrySet()) {
-			modifiedExpression = replacement.getKey().matcher(modifiedExpression)
-					.replaceAll(replacement.getValue());
-		}
-
-		// the previous operation breaks negative numbers, fix them!
-		// (i.e. -2 becomes - 2)
-		// FIXME the previous operaton also breaks stuff like "1e-5"
-		for (int i = 0; i < modifiedExpression.length(); i++) {
-			if (modifiedExpression.charAt(i) == '-'
-					&& (i < 2 || Arrays.asList('+', '-', '*', '/', '|', '^')
-							.contains(modifiedExpression.charAt(i - 2)))) {
-				// found a broken negative number
-				modifiedExpression = modifiedExpression.substring(0, i + 1)
-						+ modifiedExpression.substring(i + 2);
-			}
-		}
-
-		return this.unitValueExpressionParser.parseExpression(modifiedExpression);
+		return this.unitValueExpressionParser
+				.parseExpression(formatExpression(expression));
 	}
 
 	/**
 	 * Gets a unit dimension from the database using its name.
-	 * 
+	 *
 	 * @param name dimension's name
 	 * @return dimension
 	 * @since 2019-03-14
@@ -1594,12 +1553,11 @@ public final class UnitDatabase {
 	 */
 	public ObjectProduct<BaseDimension> getDimension(final String name) {
 		Objects.requireNonNull(name, "name must not be null.");
-		final ObjectProduct<BaseDimension> dimension = this.dimensions.get(name);
+		final var dimension = this.dimensions.get(name);
 		if (dimension == null)
 			throw new NoSuchElementException(
 					"No dimension with name \"" + name + "\".");
-		else
-			return dimension;
+		return dimension;
 	}
 
 	/**
@@ -1614,8 +1572,9 @@ public final class UnitDatabase {
 	 * multiplication)</li>
 	 * <li>The operator '^' which exponentiates. Exponents must be integers.</li>
 	 * </ul>
-	 * 
+	 *
 	 * @param expression expression to parse
+	 * @return parsed unit dimension
 	 * @throws IllegalArgumentException if the expression cannot be parsed
 	 * @throws NullPointerException     if expression is null
 	 * @since 2019-04-13
@@ -1629,23 +1588,14 @@ public final class UnitDatabase {
 		if (this.containsDimensionName(expression))
 			return this.getDimension(expression);
 
-		// force operators to have spaces
-		String modifiedExpression = expression;
-
-		// format expression
-		for (final Entry<Pattern, String> replacement : EXPRESSION_REPLACEMENTS
-				.entrySet()) {
-			modifiedExpression = replacement.getKey().matcher(modifiedExpression)
-					.replaceAll(replacement.getValue());
-		}
-
-		return this.unitDimensionParser.parseExpression(modifiedExpression);
+		return this.unitDimensionParser
+				.parseExpression(formatExpression(expression));
 	}
 
 	/**
 	 * Gets a unit. If it is linear, cast it to a LinearUnit and return it.
 	 * Otherwise, throw an {@code IllegalArgumentException}.
-	 * 
+	 *
 	 * @param name unit's name
 	 * @return unit
 	 * @since 2019-03-22
@@ -1662,29 +1612,28 @@ public final class UnitDatabase {
 						"Format nonlinear units like: unit(value).");
 
 			// solve the function
-			final Unit unit = this.getUnit(parts.get(0));
-			final double value = Double.parseDouble(
+			final var unit = this.getUnit(parts.get(0));
+			final var value = Double.parseDouble(
 					parts.get(1).substring(0, parts.get(1).length() - 1));
 			return LinearUnit.fromUnitValue(unit, value);
-		} else {
-			// get a linear unit
-			final Unit unit = this.getUnit(name);
-
-			if (unit instanceof LinearUnit)
-				return (LinearUnit) unit;
-			else
-				throw new IllegalArgumentException(
-						String.format("%s is not a linear unit.", name));
 		}
+		// get a linear unit
+		final var unit = this.getUnit(name);
+
+		if (unit instanceof LinearUnit)
+			return (LinearUnit) unit;
+		throw new IllegalArgumentException(
+				String.format("%s is not a linear unit.", name));
 	}
 
 	/**
 	 * Gets a {@code LinearUnitValue} from a unit name. Nonlinear units will be
 	 * converted to their base units.
-	 * 
+	 *
 	 * @param name name of unit
 	 * @return {@code LinearUnitValue} instance
 	 * @since 2020-08-04
+	 * @since v0.3.0
 	 */
 	LinearUnitValue getLinearUnitValue(final String name) {
 		try {
@@ -1698,7 +1647,7 @@ public final class UnitDatabase {
 
 	/**
 	 * Gets a unit prefix from the database from its name
-	 * 
+	 *
 	 * @param name prefix's name
 	 * @return prefix
 	 * @since 2019-01-10
@@ -1708,30 +1657,30 @@ public final class UnitDatabase {
 		try {
 			return UnitPrefix.valueOf(Double.parseDouble(name));
 		} catch (final NumberFormatException e) {
-			final UnitPrefix prefix = this.prefixes.get(name);
+			final var prefix = this.prefixes.get(name);
 			if (prefix == null)
 				throw new NoSuchElementException(
 						"No prefix with name \"" + name + "\".");
-			else
-				return prefix;
+			return prefix;
 		}
 	}
 
 	/**
 	 * Gets all of the prefixes that are on a unit name, in application order.
-	 * 
+	 *
 	 * @param unitName name of unit
 	 * @return prefixes
 	 * @since 2020-08-26
+	 * @since v0.3.0
 	 */
 	List<UnitPrefix> getPrefixesFromName(final String unitName) {
 		final List<UnitPrefix> prefixes = new ArrayList<>();
-		String name = unitName;
+		var name = unitName;
 
 		while (!this.prefixlessUnits.containsKey(name)) {
 			// find the longest prefix
 			String longestPrefixName = null;
-			int longestLength = name.length();
+			var longestLength = name.length();
 
 			while (longestPrefixName == null) {
 				longestLength--;
@@ -1744,7 +1693,7 @@ public final class UnitDatabase {
 			}
 
 			// longest prefix found!
-			final UnitPrefix prefix = this.getPrefix(longestPrefixName);
+			final var prefix = this.getPrefix(longestPrefixName);
 			prefixes.add(0, prefix);
 			name = name.substring(longestLength);
 		}
@@ -1757,7 +1706,7 @@ public final class UnitDatabase {
 	 * Currently, prefix expressions are much simpler than unit expressions: They
 	 * are either a number or the name of another prefix
 	 * </p>
-	 * 
+	 *
 	 * @param expression expression to input
 	 * @return prefix
 	 * @throws IllegalArgumentException if expression cannot be parsed
@@ -1772,30 +1721,22 @@ public final class UnitDatabase {
 		if (this.containsUnitName(expression))
 			return this.getPrefix(expression);
 
-		// force operators to have spaces
-		String modifiedExpression = expression;
-
-		// format expression
-		for (final Entry<Pattern, String> replacement : EXPRESSION_REPLACEMENTS
-				.entrySet()) {
-			modifiedExpression = replacement.getKey().matcher(modifiedExpression)
-					.replaceAll(replacement.getValue());
-		}
-
-		return this.prefixExpressionParser.parseExpression(modifiedExpression);
+		return this.prefixExpressionParser
+				.parseExpression(formatExpression(expression));
 	}
 
 	/**
 	 * @return the prefixRepetitionRule
 	 * @since 2020-08-26
+	 * @since v0.3.0
 	 */
-	public final Predicate<List<UnitPrefix>> getPrefixRepetitionRule() {
+	public Predicate<List<UnitPrefix>> getPrefixRepetitionRule() {
 		return this.prefixRepetitionRule;
 	}
 
 	/**
 	 * Gets a unit from the database from its name, looking for prefixes.
-	 * 
+	 *
 	 * @param name unit's name
 	 * @return unit
 	 * @since 2019-01-10
@@ -1803,27 +1744,28 @@ public final class UnitDatabase {
 	 */
 	public Unit getUnit(final String name) {
 		try {
-			final double value = Double.parseDouble(name);
+			final var value = Double.parseDouble(name);
 			return Metric.ONE.times(value);
 		} catch (final NumberFormatException e) {
-			final Unit unit = this.units.get(name);
+			final var unit = this.units.get(name);
 			if (unit == null)
 				throw new NoSuchElementException("No unit " + name);
-			else if (unit.getPrimaryName().isEmpty())
+			if (unit.getPrimaryName().isEmpty())
 				return unit.withName(NameSymbol.ofName(name));
-			else if (!unit.getPrimaryName().get().equals(name)) {
+			if (!unit.getPrimaryName().get().equals(name)) {
 				final Set<String> otherNames = new HashSet<>(unit.getOtherNames());
 				otherNames.add(unit.getPrimaryName().get());
 				return unit.withName(NameSymbol.ofNullable(name,
 						unit.getSymbol().orElse(null), otherNames));
-			} else if (!unit.getOtherNames().contains(name)) {
+			}
+			if (!unit.getOtherNames().contains(name)) {
 				final Set<String> otherNames = new HashSet<>(unit.getOtherNames());
 				otherNames.add(name);
 				return unit.withName(
 						NameSymbol.ofNullable(unit.getPrimaryName().orElse(null),
 								unit.getSymbol().orElse(null), otherNames));
-			} else
-				return unit;
+			}
+			return unit;
 		}
 
 	}
@@ -1842,8 +1784,9 @@ public final class UnitDatabase {
 	 * <li>A number which is multiplied or divided</li>
 	 * </ul>
 	 * This method only works with linear units.
-	 * 
+	 *
 	 * @param expression expression to parse
+	 * @return parsed unit
 	 * @throws IllegalArgumentException if the expression cannot be parsed
 	 * @throws NullPointerException     if expression is null
 	 * @since 2019-01-07
@@ -1856,31 +1799,51 @@ public final class UnitDatabase {
 		if (this.containsUnitName(expression))
 			return this.getUnit(expression);
 
-		// force operators to have spaces
-		String modifiedExpression = expression;
-		modifiedExpression = modifiedExpression.replaceAll("\\+", " \\+ ");
-		modifiedExpression = modifiedExpression.replaceAll("-", " - ");
+		return this.unitExpressionParser
+				.parseExpression(formatExpression(expression));
+	}
 
-		// format expression
-		for (final Entry<Pattern, String> replacement : EXPRESSION_REPLACEMENTS
-				.entrySet()) {
-			modifiedExpression = replacement.getKey().matcher(modifiedExpression)
-					.replaceAll(replacement.getValue());
-		}
+	/**
+	 * Get a unit set from its name, throwing a {@link NoSuchElementException} if
+	 * there is none.
+	 *
+	 * @param name name of unit set
+	 * @return unit set with that name
+	 *
+	 * @since 2024-08-16
+	 * @since v1.0.0
+	 */
+	public List<LinearUnit> getUnitSet(String name) {
+		final var unitSet = this.unitSets.get(name);
+		if (unitSet == null)
+			throw new NoSuchElementException("No unit set with name " + name);
+		return unitSet;
+	}
 
-		// the previous operation breaks negative numbers, fix them!
-		// (i.e. -2 becomes - 2)
-		for (int i = 0; i < modifiedExpression.length(); i++) {
-			if (modifiedExpression.charAt(i) == '-'
-					&& (i < 2 || Arrays.asList('+', '-', '*', '/', '|', '^')
-							.contains(modifiedExpression.charAt(i - 2)))) {
-				// found a broken negative number
-				modifiedExpression = modifiedExpression.substring(0, i + 1)
-						+ modifiedExpression.substring(i + 2);
-			}
-		}
+	/**
+	 * Parses a semicolon-separated expression to get the unit set being used.
+	 *
+	 * @since 2024-08-22
+	 * @since v1.0.0
+	 */
+	List<LinearUnit> getUnitSetFromExpression(String expression) {
+		final var parts = expression.split(";");
+		final List<LinearUnit> units = new ArrayList<>(parts.length);
+		for (final String unitName : parts) {
+			final var unit = this.getUnitFromExpression(unitName.trim());
 
-		return this.unitExpressionParser.parseExpression(modifiedExpression);
+			if (!(unit instanceof LinearUnit))
+				throw new IllegalArgumentException(String.format(
+						"Unit '%s' is in a unit-set expression, but is not linear.",
+						unitName));
+			if (units.size() > 0 && !unit.canConvertTo(units.get(0)))
+				throw new IllegalArgumentException(String.format(
+						"Units in expression '%s' have different dimensions.",
+						expression));
+
+			units.add((LinearUnit) unit);
+		}
+		return units;
 	}
 
 	/**
@@ -1901,26 +1864,32 @@ public final class UnitDatabase {
 	 * no unit is found, an IllegalArgumentException is thrown. This is used to
 	 * define initial units and ensure that the database contains them.</li>
 	 * </ul>
-	 * 
+	 *
 	 * @param file file to read
-	 * @throws IllegalArgumentException if the file cannot be parsed, found or
-	 *                                  read
-	 * @throws NullPointerException     if file is null
+	 * @throws NullPointerException if file is null
+	 * @return list of errors that happened when loading file
 	 * @since 2019-01-13
 	 * @since v0.1.0
 	 */
-	public void loadDimensionFile(final Path file) {
+	public List<LoadingException> loadDimensionFile(final Path file) {
 		Objects.requireNonNull(file, "file must not be null.");
+		final List<LoadingException> errors = new ArrayList<>();
 		try {
-			long lineCounter = 0;
+			var lineCounter = 0L;
 			for (final String line : Files.readAllLines(file)) {
-				this.addDimensionFromLine(line, ++lineCounter);
+				try {
+					this.addDimensionFromLine(line, ++lineCounter);
+				} catch (IllegalArgumentException | NoSuchElementException e) {
+					errors.add(new LoadingException(lineCounter, line, file,
+							LoadingException.FileType.DIMENSION, e));
+				}
 			}
 		} catch (final FileNotFoundException e) {
 			throw new IllegalArgumentException("Could not find file " + file, e);
 		} catch (final IOException e) {
 			throw new IllegalArgumentException("Could not read file " + file, e);
 		}
+		return errors;
 	}
 
 	/**
@@ -1928,15 +1897,26 @@ public final class UnitDatabase {
 	 * {@link #loadDimensionFile}.
 	 *
 	 * @param stream stream to load from
+	 * @return list of all errors that happened loading the stream
 	 * @since 2021-03-27
+	 * @since v0.3.0
 	 */
-	public void loadDimensionsFromStream(final InputStream stream) {
-		try (final Scanner scanner = new Scanner(stream)) {
-			long lineCounter = 0;
+	public List<LoadingException> loadDimensionsFromStream(
+			final InputStream stream) {
+		final List<LoadingException> errors = new ArrayList<>();
+		try (final var scanner = new Scanner(stream)) {
+			var lineCounter = 0L;
 			while (scanner.hasNextLine()) {
-				this.addDimensionFromLine(scanner.nextLine(), ++lineCounter);
+				final var line = scanner.nextLine();
+				try {
+					this.addDimensionFromLine(line, ++lineCounter);
+				} catch (IllegalArgumentException | NoSuchElementException e) {
+					errors.add(new LoadingException(lineCounter, line,
+							LoadingException.FileType.DIMENSION, e));
+				}
 			}
 		}
+		return errors;
 	}
 
 	/**
@@ -1956,26 +1936,32 @@ public final class UnitDatabase {
 	 * no unit is found, an IllegalArgumentException is thrown. This is used to
 	 * define initial units and ensure that the database contains them.</li>
 	 * </ul>
-	 * 
+	 *
 	 * @param file file to read
-	 * @throws IllegalArgumentException if the file cannot be parsed, found or
-	 *                                  read
-	 * @throws NullPointerException     if file is null
+	 * @throws NullPointerException if file is null
+	 * @return list of errors that happened when loading file
 	 * @since 2019-01-13
 	 * @since v0.1.0
 	 */
-	public void loadUnitsFile(final Path file) {
+	public List<LoadingException> loadUnitsFile(final Path file) {
 		Objects.requireNonNull(file, "file must not be null.");
+		final List<LoadingException> errors = new ArrayList<>();
 		try {
-			long lineCounter = 0;
+			var lineCounter = 0L;
 			for (final String line : Files.readAllLines(file)) {
-				this.addUnitOrPrefixFromLine(line, ++lineCounter);
+				try {
+					this.addUnitOrPrefixFromLine(line, ++lineCounter);
+				} catch (IllegalArgumentException | NoSuchElementException e) {
+					errors.add(new LoadingException(lineCounter, line, file,
+							LoadingException.FileType.UNIT, e));
+				}
 			}
 		} catch (final FileNotFoundException e) {
 			throw new IllegalArgumentException("Could not find file " + file, e);
 		} catch (final IOException e) {
 			throw new IllegalArgumentException("Could not read file " + file, e);
 		}
+		return errors;
 	}
 
 	/**
@@ -1983,15 +1969,25 @@ public final class UnitDatabase {
 	 * {@link #loadUnitsFile}.
 	 *
 	 * @param stream stream to load from
+	 * @return list of all errors that happened loading the stream
 	 * @since 2021-03-27
+	 * @since v0.3.0
 	 */
-	public void loadUnitsFromStream(InputStream stream) {
-		try (final Scanner scanner = new Scanner(stream)) {
-			long lineCounter = 0;
+	public List<LoadingException> loadUnitsFromStream(InputStream stream) {
+		final List<LoadingException> errors = new ArrayList<>();
+		try (final var scanner = new Scanner(stream)) {
+			var lineCounter = 0L;
 			while (scanner.hasNextLine()) {
-				this.addUnitOrPrefixFromLine(scanner.nextLine(), ++lineCounter);
+				final var line = scanner.nextLine();
+				try {
+					this.addUnitOrPrefixFromLine(line, ++lineCounter);
+				} catch (IllegalArgumentException | NoSuchElementException e) {
+					errors.add(new LoadingException(lineCounter, line,
+							LoadingException.FileType.UNIT, e));
+				}
 			}
 		}
+		return errors;
 	}
 
 	/**
@@ -2003,17 +1999,17 @@ public final class UnitDatabase {
 	public Map<String, UnitPrefix> prefixMap(boolean includeDuplicates) {
 		if (includeDuplicates)
 			return Collections.unmodifiableMap(this.prefixes);
-		else
-			return Collections.unmodifiableMap(ConditionalExistenceCollections
-					.conditionalExistenceMap(this.prefixes,
-							entry -> !isRemovableDuplicate(this.prefixes, entry)));
+		return Collections.unmodifiableMap(ConditionalExistenceCollections
+				.conditionalExistenceMap(this.prefixes,
+						entry -> !isRemovableDuplicate(this.prefixes, entry)));
 	}
 
 	/**
 	 * @param prefixRepetitionRule the prefixRepetitionRule to set
 	 * @since 2020-08-26
+	 * @since v0.3.0
 	 */
-	public final void setPrefixRepetitionRule(
+	public void setPrefixRepetitionRule(
 			Predicate<List<UnitPrefix>> prefixRepetitionRule) {
 		this.prefixRepetitionRule = prefixRepetitionRule;
 	}
@@ -2041,18 +2037,18 @@ public final class UnitDatabase {
 	 * <p>
 	 * Specifically, the operations that will throw an IllegalStateException if
 	 * the map is infinite in size are:
+	 * </p>
 	 * <ul>
 	 * <li>{@code unitMap.entrySet().toArray()} (either overloading)</li>
 	 * <li>{@code unitMap.keySet().toArray()} (either overloading)</li>
 	 * </ul>
-	 * </p>
 	 * <p>
 	 * Because of ambiguities between prefixes (i.e. kilokilo = mega), the map's
 	 * {@link PrefixedUnitMap#containsValue containsValue} and
 	 * {@link PrefixedUnitMap#values() values()} methods currently ignore
 	 * prefixes.
 	 * </p>
-	 * 
+	 *
 	 * @return a map mapping unit names to units, including prefixed names
 	 * @since 2019-04-13
 	 * @since v0.2.0
@@ -2073,10 +2069,17 @@ public final class UnitDatabase {
 	public Map<String, Unit> unitMapPrefixless(boolean includeDuplicates) {
 		if (includeDuplicates)
 			return Collections.unmodifiableMap(this.prefixlessUnits);
-		else
-			return Collections.unmodifiableMap(ConditionalExistenceCollections
-					.conditionalExistenceMap(this.prefixlessUnits,
-							entry -> !isRemovableDuplicate(this.prefixlessUnits,
-									entry)));
+		return Collections.unmodifiableMap(ConditionalExistenceCollections
+				.conditionalExistenceMap(this.prefixlessUnits,
+						entry -> !isRemovableDuplicate(this.prefixlessUnits, entry)));
+	}
+
+	/**
+	 * @return an unmodifiable map mapping names to unit sets
+	 * @since 2024-08-16
+	 * @since v1.0.0
+	 */
+	public Map<String, List<LinearUnit>> unitSetMap() {
+		return Collections.unmodifiableMap(this.unitSets);
 	}
 }