Keep track of identifiers separately for each SubFunctionPattern object

core/src/main/java/it/cavallium/warppi/math/rules/dsl/Pattern.java

@@ -7,7 +7,7 @@ import it.cavallium.warppi.math.rules.dsl.patterns.SubFunctionPattern;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Recognizes and generates functions of some specific shape.
@@ -51,8 +51,10 @@ public interface Pattern {
 	Function replace(MathContext mathContext, Map<String, Function> subFunctions);
 
 	/**
-	 * @return The (possibly empty) <code>Set</code> of all sub-function patterns
+	 * @return A (possibly empty) <code>Stream</code> of all sub-function patterns
 	 *         found within this pattern and its children.
+	 *         If there are multiple sub-function patterns with the same name, the stream still contains all of them.
+	 *         The order of the patterns within the stream is unspecified.
 	 */
-	Set<SubFunctionPattern> getSubFunctions();
+	Stream<SubFunctionPattern> getSubFunctions();
 }

core/src/main/java/it/cavallium/warppi/math/rules/dsl/PatternRule.java

@@ -52,11 +52,11 @@ public class PatternRule implements Rule {
 		return ruleType;
 	}
 
-	Pattern getTarget() {
+	public Pattern getTarget() {
 		return target;
 	}
 
-	List<Pattern> getReplacements() {
+	public List<Pattern> getReplacements() {
 		return replacements;
 	}
 

core/src/main/java/it/cavallium/warppi/math/rules/dsl/PatternUtils.java

@@ -1,26 +0,0 @@
-package it.cavallium.warppi.math.rules.dsl;
-
-import it.cavallium.warppi.math.rules.dsl.patterns.SubFunctionPattern;
-
-import java.util.*;
-import java.util.stream.Collectors;
-
-/**
- * Contains helper methods which are useful for writing patterns.
- */
-public class PatternUtils {
-	private PatternUtils() {}
-
-	/**
-	 * Gathers all sub-function patterns from multiple patterns.
-	 *
-	 * @param patterns The patterns from which sub-functions are gathered.
-	 * @return The union of the return values of {@link Pattern#getSubFunctions()} for each pattern.
-	 */
-	public static Set<SubFunctionPattern> getSubFunctionsFrom(final Pattern... patterns) {
-		return Arrays.stream(patterns)
-				.map(Pattern::getSubFunctions)
-				.flatMap(Set::stream)
-				.collect(Collectors.toSet());
-	}
-}

core/src/main/java/it/cavallium/warppi/math/rules/dsl/RulesDsl.java

@@ -6,6 +6,8 @@ import it.cavallium.warppi.math.rules.dsl.frontend.Parser;
 import it.cavallium.warppi.math.rules.dsl.patterns.SubFunctionPattern;
 
 import java.util.*;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 /**
  * Implements a domain-specific language (DSL) for the definition of {@link Rule}s.
@@ -28,9 +30,10 @@ public class RulesDsl {
 		final List<PatternRule> rules = parser.parse();
 
 		for (final PatternRule rule : rules) {
-			undefinedSubFunctions(rule).stream()
+			undefinedSubFunctions(rule)
-					.flatMap(subFunc -> parser.getSubFunctionIdentifiers(rule, subFunc).stream())
+					.map(subFunc -> new UndefinedSubFunction(
-					.map(UndefinedSubFunction::new)
+						parser.getSubFunctionIdentifier(subFunc)
+					))
 					.forEach(errors::add);
 		}
 
@@ -46,15 +49,12 @@ public class RulesDsl {
 	 * without being defined (captured) in the target pattern.
 	 *
 	 * @param rule The rule to analyze.
-	 * @return The (possibly empty) set of undefined sub-functions.
+	 * @return A (possibly empty) <code>Stream</code> of undefined sub-functions.
 	 */
-	private static Set<SubFunctionPattern> undefinedSubFunctions(final PatternRule rule) {
+	private static Stream<SubFunctionPattern> undefinedSubFunctions(final PatternRule rule) {
-		final Set<SubFunctionPattern> defined = rule.getTarget().getSubFunctions();
+		final Set<SubFunctionPattern> defined = rule.getTarget().getSubFunctions().collect(Collectors.toSet());
-		final Set<SubFunctionPattern> undefined = new HashSet<>();
+		return rule.getReplacements().stream()
-		for (final Pattern replacement : rule.getReplacements()) {
+			.flatMap(Pattern::getSubFunctions)
-			undefined.addAll(replacement.getSubFunctions());
+			.filter(subFunc -> !defined.contains(subFunc));
-		}
-		undefined.removeAll(defined);
-		return undefined;
 	}
 }

core/src/main/java/it/cavallium/warppi/math/rules/dsl/frontend/Parser.java

@@ -32,10 +32,8 @@ public class Parser {
 	private int currentIndex = 0;
 
 	// For error reporting
-	private Map<SubFunctionPattern, List<Token>> ruleSubFunctionIdentifiers;
+	// An IdentityHashMap is used to distinguish SubFunctionPatterns even if they're identical (equal)
-	// An IdentityHashMap is used to distinguish rules even if they're identical (equal)
+	private final IdentityHashMap<SubFunctionPattern, Token> subFunctionIdentifiers = new IdentityHashMap<>();
-	private final IdentityHashMap<PatternRule, Map<SubFunctionPattern, List<Token>>> subFunctionIdentifiers =
-			new IdentityHashMap<>();
 
 	/**
 	 * Constructs a <code>Parser</code> that will produce a list of {@link PatternRule}s from the the given list of {@link Token}s.
@@ -64,8 +62,21 @@ public class Parser {
 		return rules();
 	}
 
-	public List<Token> getSubFunctionIdentifiers(final PatternRule rule, final SubFunctionPattern subFunction) {
+	/**
-		return subFunctionIdentifiers.get(rule).get(subFunction);
+	 * Retrieves the <code>IDENTIFIER</code> token which corresponds to the given <code>SubFunctionPattern</code>.
+	 * <p>
+	 * The information returned by this method can be used to point out the location of sub-function related errors
+	 * within the DSL source code.
+	 *
+	 * @param subFunction a <code>SubFunctionsPattern</code> from one of the rules returned by this <code>Parser</code>
+	 *                    instance. While <code>SubFunctionPattern</code>s with the same name are considered equal,
+	 *                    this method can distinguish between them, in order to return the exact identifier which led
+	 *                    to the creation of the specified <code>SubFunctionPattern</code> object.
+	 * @return the <code>Token</code> (of type <code>IDENTIFIER</code>) which corresponds to the given
+	 * 	       <code>SubFunctionPattern</code>.
+	 */
+	public Token getSubFunctionIdentifier(final SubFunctionPattern subFunction) {
+		return subFunctionIdentifiers.get(subFunction);
 	}
 
 	// rules = { rule } , EOF ;
@@ -88,14 +99,11 @@ public class Parser {
 	private PatternRule rule() throws SyntaxException {
 		final RuleType type = ruleType();
 		final String name = matchOrFail(IDENTIFIER).lexeme;
-		ruleSubFunctionIdentifiers = new HashMap<>(); // Must be initialized before calling pattern() and replacements()
 		matchOrFail(COLON);
 		final Pattern target = pattern();
 		matchOrFail(ARROW);
 		final List<Pattern> replacements = replacements();
-		final PatternRule rule = new PatternRule(name, type, target, replacements);
+		return new PatternRule(name, type, target, replacements);
-		subFunctionIdentifiers.put(rule, ruleSubFunctionIdentifiers);
-		return rule;
 	}
 
 	// rule type = REDUCTION | EXPANSION | CALCULATION | EXISTENCE ;
@@ -247,7 +255,7 @@ public class Parser {
 				return new NumberPattern(new BigDecimal(curToken.lexeme));
 			case IDENTIFIER:
 				final SubFunctionPattern subFunction = new SubFunctionPattern(curToken.lexeme);
-				saveSubFunctionIdentifier(subFunction, curToken);
+				subFunctionIdentifiers.put(subFunction, curToken);
 				return subFunction;
 			case LEFT_PAREN:
 				final Pattern grouped = sum();
@@ -257,14 +265,6 @@ public class Parser {
 		throw new SyntaxException(new UnexpectedToken(curToken));
 	}
 
-	private void saveSubFunctionIdentifier(final SubFunctionPattern subFunction, final Token curToken) {
-		final List<Token> subFunctionList = ruleSubFunctionIdentifiers.computeIfAbsent(
-				subFunction,
-				key -> new ArrayList<>()
-		);
-		subFunctionList.add(curToken);
-	}
-
 	private Pattern matchLeftAssoc(
 			final PatternParser operandParser,
 			final Map<TokenType, BiFunction<Pattern, Pattern, Pattern>> operators

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/ArcCosinePattern.java

@@ -8,7 +8,7 @@ import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates the arccosine of another pattern.
@@ -34,7 +34,7 @@ public class ArcCosinePattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
 		return argument.getSubFunctions();
 	}
 

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/ArcSinePattern.java

@@ -8,7 +8,7 @@ import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates the arcsine of another pattern.
@@ -34,7 +34,7 @@ public class ArcSinePattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
 		return argument.getSubFunctions();
 	}
 

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/ArcTangentPattern.java

@@ -8,7 +8,7 @@ import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates the arctangent of another pattern.
@@ -34,7 +34,7 @@ public class ArcTangentPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
 		return argument.getSubFunctions();
 	}
 

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/ConstantPattern.java

@@ -5,10 +5,9 @@ import it.cavallium.warppi.math.MathContext;
 import it.cavallium.warppi.math.functions.Variable;
 import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
-import java.util.Collections;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates a specific symbolic constant.
@@ -32,8 +31,8 @@ public class ConstantPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return Collections.emptySet();
+		return Stream.empty();
 	}
 
 	@Override

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/CosinePattern.java

@@ -8,7 +8,7 @@ import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates the cosine of another pattern.
@@ -34,7 +34,7 @@ public class CosinePattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
 		return argument.getSubFunctions();
 	}
 

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/DivisionPattern.java

@@ -4,12 +4,11 @@ import it.cavallium.warppi.math.Function;
 import it.cavallium.warppi.math.MathContext;
 import it.cavallium.warppi.math.functions.Division;
 import it.cavallium.warppi.math.rules.dsl.Pattern;
-import it.cavallium.warppi.math.rules.dsl.PatternUtils;
 import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates a division of two other patterns.
@@ -39,8 +38,9 @@ public class DivisionPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return PatternUtils.getSubFunctionsFrom(dividend, divisor);
+		return Stream.of(dividend, divisor)
+			.flatMap(Pattern::getSubFunctions);
 	}
 
 	@Override

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/EquationPattern.java

@@ -4,12 +4,11 @@ import it.cavallium.warppi.math.Function;
 import it.cavallium.warppi.math.MathContext;
 import it.cavallium.warppi.math.functions.equations.Equation;
 import it.cavallium.warppi.math.rules.dsl.Pattern;
-import it.cavallium.warppi.math.rules.dsl.PatternUtils;
 import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates an equation of two other patterns.
@@ -39,8 +38,9 @@ public class EquationPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return PatternUtils.getSubFunctionsFrom(left, right);
+		return Stream.of(left, right)
+			.flatMap(Pattern::getSubFunctions);
 	}
 
 	@Override

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/EquationsSystemPattern.java

@@ -4,12 +4,11 @@ import it.cavallium.warppi.math.Function;
 import it.cavallium.warppi.math.MathContext;
 import it.cavallium.warppi.math.functions.equations.EquationsSystem;
 import it.cavallium.warppi.math.rules.dsl.Pattern;
-import it.cavallium.warppi.math.rules.dsl.PatternUtils;
 import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Arrays;
 import java.util.Map;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates a system of equations of multiple other patterns.
@@ -47,8 +46,9 @@ public class EquationsSystemPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return PatternUtils.getSubFunctionsFrom(patterns);
+		return Stream.of(patterns)
+			.flatMap(Pattern::getSubFunctions);
 	}
 
 	@Override

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/LogarithmPattern.java

@@ -4,12 +4,11 @@ import it.cavallium.warppi.math.Function;
 import it.cavallium.warppi.math.MathContext;
 import it.cavallium.warppi.math.functions.Logarithm;
 import it.cavallium.warppi.math.rules.dsl.Pattern;
-import it.cavallium.warppi.math.rules.dsl.PatternUtils;
 import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates a logarithm of base and argument patterns.
@@ -39,8 +38,9 @@ public class LogarithmPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return PatternUtils.getSubFunctionsFrom(base, argument);
+		return Stream.of(base, argument)
+			.flatMap(Pattern::getSubFunctions);
 	}
 
 	@Override

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/MultiplicationPattern.java

@@ -4,12 +4,11 @@ import it.cavallium.warppi.math.Function;
 import it.cavallium.warppi.math.MathContext;
 import it.cavallium.warppi.math.functions.Multiplication;
 import it.cavallium.warppi.math.rules.dsl.Pattern;
-import it.cavallium.warppi.math.rules.dsl.PatternUtils;
 import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates a multiplication of two other patterns.
@@ -39,8 +38,9 @@ public class MultiplicationPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return PatternUtils.getSubFunctionsFrom(left, right);
+		return Stream.of(left, right)
+			.flatMap(Pattern::getSubFunctions);
 	}
 
 	@Override

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/NegativePattern.java

@@ -10,7 +10,7 @@ import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 import java.math.BigDecimal;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates the negative of another pattern.
@@ -52,7 +52,7 @@ public class NegativePattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
 		return inner.getSubFunctions();
 	}
 

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/NumberPattern.java

@@ -6,10 +6,9 @@ import it.cavallium.warppi.math.functions.Number;
 import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.math.BigDecimal;
-import java.util.Collections;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates a specific number.
@@ -32,8 +31,8 @@ public class NumberPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return Collections.emptySet();
+		return Stream.empty();
 	}
 
 	@Override

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/PowerPattern.java

@@ -4,12 +4,11 @@ import it.cavallium.warppi.math.Function;
 import it.cavallium.warppi.math.MathContext;
 import it.cavallium.warppi.math.functions.Power;
 import it.cavallium.warppi.math.rules.dsl.Pattern;
-import it.cavallium.warppi.math.rules.dsl.PatternUtils;
 import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates a power (exponentiation) of base and exponent patterns.
@@ -39,8 +38,9 @@ public class PowerPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return PatternUtils.getSubFunctionsFrom(base, exponent);
+		return Stream.of(base, exponent)
+			.flatMap(Pattern::getSubFunctions);
 	}
 
 	@Override

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/RootPattern.java

@@ -6,13 +6,12 @@ import it.cavallium.warppi.math.functions.Number;
 import it.cavallium.warppi.math.functions.Root;
 import it.cavallium.warppi.math.functions.RootSquare;
 import it.cavallium.warppi.math.rules.dsl.Pattern;
-import it.cavallium.warppi.math.rules.dsl.PatternUtils;
 import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.math.BigDecimal;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates a root of degree and radicand patterns.
@@ -54,8 +53,9 @@ public class RootPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return PatternUtils.getSubFunctionsFrom(degree, radicand);
+		return Stream.of(degree, radicand)
+			.flatMap(Pattern::getSubFunctions);
 	}
 
 	@Override

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/SinePattern.java

@@ -8,7 +8,7 @@ import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates the sine of another pattern.
@@ -34,7 +34,7 @@ public class SinePattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
 		return argument.getSubFunctions();
 	}
 

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/SubFunctionPattern.java

@@ -4,10 +4,9 @@ import it.cavallium.warppi.math.Function;
 import it.cavallium.warppi.math.MathContext;
 import it.cavallium.warppi.math.rules.dsl.Pattern;
 
-import java.util.Collections;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates any function as a named sub-function.
@@ -31,8 +30,8 @@ public class SubFunctionPattern implements Pattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return Collections.singleton(this);
+		return Stream.of(this);
 	}
 
 	@Override

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/SubtractionPattern.java

@@ -4,12 +4,11 @@ import it.cavallium.warppi.math.Function;
 import it.cavallium.warppi.math.MathContext;
 import it.cavallium.warppi.math.functions.Subtraction;
 import it.cavallium.warppi.math.rules.dsl.Pattern;
-import it.cavallium.warppi.math.rules.dsl.PatternUtils;
 import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates a subtraction of two other patterns.
@@ -39,8 +38,9 @@ public class SubtractionPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return PatternUtils.getSubFunctionsFrom(left, right);
+		return Stream.of(left, right)
+			.flatMap(Pattern::getSubFunctions);
 	}
 
 	@Override

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/SumPattern.java

@@ -4,12 +4,11 @@ import it.cavallium.warppi.math.Function;
 import it.cavallium.warppi.math.MathContext;
 import it.cavallium.warppi.math.functions.Sum;
 import it.cavallium.warppi.math.rules.dsl.Pattern;
-import it.cavallium.warppi.math.rules.dsl.PatternUtils;
 import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates a sum of two other patterns.
@@ -39,8 +38,9 @@ public class SumPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return PatternUtils.getSubFunctionsFrom(left, right);
+		return Stream.of(left, right)
+			.flatMap(Pattern::getSubFunctions);
 	}
 
 	@Override

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/SumSubtractionPattern.java

@@ -4,12 +4,11 @@ import it.cavallium.warppi.math.Function;
 import it.cavallium.warppi.math.MathContext;
 import it.cavallium.warppi.math.functions.SumSubtraction;
 import it.cavallium.warppi.math.rules.dsl.Pattern;
-import it.cavallium.warppi.math.rules.dsl.PatternUtils;
 import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates a sum/subtraction (±) of two other patterns.
@@ -39,8 +38,9 @@ public class SumSubtractionPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return PatternUtils.getSubFunctionsFrom(left, right);
+		return Stream.of(left, right)
+			.flatMap(Pattern::getSubFunctions);
 	}
 
 	@Override

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/TangentPattern.java

@@ -8,7 +8,7 @@ import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates the tangent of another pattern.
@@ -34,7 +34,7 @@ public class TangentPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
 		return argument.getSubFunctions();
 	}
 

core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/UndefinedPattern.java

@@ -5,9 +5,8 @@ import it.cavallium.warppi.math.MathContext;
 import it.cavallium.warppi.math.functions.Undefined;
 import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
 
-import java.util.Collections;
 import java.util.Map;
-import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Matches and generates <code>Undefined</code>.
@@ -24,8 +23,8 @@ public class UndefinedPattern extends VisitorPattern {
 	}
 
 	@Override
-	public Set<SubFunctionPattern> getSubFunctions() {
+	public Stream<SubFunctionPattern> getSubFunctions() {
-		return Collections.emptySet();
+		return Stream.empty();
 	}
 
 	@Override

core/src/test/java/it/cavallium/warppi/math/rules/dsl/frontend/ParserTest.java

@@ -6,6 +6,7 @@ import it.cavallium.warppi.math.rules.dsl.DslError;
 import it.cavallium.warppi.math.rules.dsl.Pattern;
 import it.cavallium.warppi.math.rules.dsl.PatternRule;
 import it.cavallium.warppi.math.rules.dsl.patterns.*;
+import org.apache.commons.lang3.ObjectUtils;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -15,6 +16,7 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 import static it.cavallium.warppi.math.rules.dsl.frontend.TokenType.*;
 import static org.junit.Assert.*;
@@ -344,21 +346,11 @@ public class ParserTest {
 		final Parser parser = new Parser(tokens, errors::add);
 		final List<PatternRule> rules = parser.parse();
 
-		assertEquals(rule0x, toReferenceEquality(
+		assertEquals(rule0x, getSubFunctionIdentifiers(parser, rules.get(0), "x"));
-				parser.getSubFunctionIdentifiers(rules.get(0), new SubFunctionPattern("x"))
+		assertEquals(rule1x, getSubFunctionIdentifiers(parser, rules.get(1), "x"));
-		));
+		assertEquals(rule1y, getSubFunctionIdentifiers(parser, rules.get(1), "y"));
-		assertEquals(rule1x, toReferenceEquality(
+		assertEquals(rule2x, getSubFunctionIdentifiers(parser, rules.get(2), "x"));
-				parser.getSubFunctionIdentifiers(rules.get(1), new SubFunctionPattern("x"))
+		assertEquals(rule3x, getSubFunctionIdentifiers(parser, rules.get(3), "x"));
-		));
-		assertEquals(rule1y, toReferenceEquality(
-				parser.getSubFunctionIdentifiers(rules.get(1), new SubFunctionPattern("y"))
-		));
-		assertEquals(rule2x, toReferenceEquality(
-				parser.getSubFunctionIdentifiers(rules.get(2), new SubFunctionPattern("x"))
-		));
-		assertEquals(rule3x, toReferenceEquality(
-				parser.getSubFunctionIdentifiers(rules.get(3), new SubFunctionPattern("x"))
-		));
 	}
 
 	private static Token addIdentifierToken(final List<ReferenceEqualityToken> list, final String identifier) {
@@ -367,9 +359,21 @@ public class ParserTest {
 		return token;
 	}
 
-	private static List<ReferenceEqualityToken> toReferenceEquality(final List<Token> tokens) {
+	private static List<ReferenceEqualityToken> getSubFunctionIdentifiers(
-		return tokens.stream()
+		final Parser parser,
-				.map(ReferenceEqualityToken::new)
+		final PatternRule rule,
+		final String subFunctionName
+	) {
+		final SubFunctionPattern exampleSubFunction = new SubFunctionPattern(subFunctionName);
+		final Stream<SubFunctionPattern> allSubFunctions = Stream.concat(
+			rule.getTarget().getSubFunctions(),
+			rule.getReplacements().stream().flatMap(Pattern::getSubFunctions)
+		);
+		return allSubFunctions
+			.filter(subFunc -> subFunc.equals(exampleSubFunction)) // Match the name without having access to it directly
+			.map(subFunc -> new ReferenceEqualityToken(
+				parser.getSubFunctionIdentifier(subFunc)
+			))
 			.collect(Collectors.toList());
 	}
 
@@ -387,6 +391,11 @@ public class ParserTest {
 			}
 			return this.token == ((ReferenceEqualityToken) o).token;
 		}
+
+		@Override
+		public String toString() {
+			return "ReferenceEqualityToken{" + ObjectUtils.identityToString(token) + '}';
+		}
 	}
 
 	// The EOF token is inserted by the lexer, therefore it can only be missing