makes implicit multiplication 2.x compatible again (#351)

README.md

@@ -28,7 +28,7 @@ strings.
 - Custom functions and operators can be added.
 - Functions can be defined with a variable number of arguments (see MIN, MAX and SUM functions).
 - Supports hexadecimal and scientific notations of numbers.
-- Supports implicit multiplication, e.g. (a+b)(a-b) or 2(x-y) which equals to (a+b)\*(a-b) or 2\*(
+- Supports implicit multiplication, e.g. 2x or (a+b)(a-b) or 2(x-y) which equals to (a+b)\*(a-b) or 2\*(
   x-y)
 - Lazy evaluation of function parameters (see the IF function) and support of sub-expressions.
 

docs/configuration/configuration.md

@@ -12,22 +12,22 @@ parameter to the _Expression_ constructor.
 Example usage, showing all default configuration values:
 
 ```java
-ExpressionConfiguration configuration = ExpressionConfiguration.builder()
-    .allowOverwriteConstants(true)
-    .arraysAllowed(true)
-    .dataAccessorSupplier(MapBasedDataAccessor::new)
-    .decimalPlacesRounding(ExpressionConfiguration.DECIMAL_PLACES_ROUNDING_UNLIMITED)
-    .defaultConstants(ExpressionConfiguration.StandardConstants)
-    .functionDictionary(ExpressionConfiguration.StandardFunctionsDictionary)
-    .implicitMultiplicationAllowed(true)
-    .mathContext(ExpressionConfiguration.DEFAULT_MATH_CONTEXT)
-    .operatorDictionary(ExpressionConfiguration.StandardOperatorsDictionary)
-    .powerOfPrecedence(OperatorIfc.OPERATOR_PRECEDENCE_POWER)
-    .stripTrailingZeros(true)
-    .structuresAllowed(true)
-    .build();
-
-Expression expression = new Expression("2.128 + a", configuration);
+ExpressionConfiguration configuration=ExpressionConfiguration.builder()
+        .allowOverwriteConstants(true)
+        .arraysAllowed(true)
+        .dataAccessorSupplier(MapBasedDataAccessor::new)
+        .decimalPlacesRounding(ExpressionConfiguration.DECIMAL_PLACES_ROUNDING_UNLIMITED)
+        .defaultConstants(ExpressionConfiguration.StandardConstants)
+        .functionDictionary(ExpressionConfiguration.StandardFunctionsDictionary)
+        .implicitMultiplicationAllowed(true)
+        .mathContext(ExpressionConfiguration.DEFAULT_MATH_CONTEXT)
+        .operatorDictionary(ExpressionConfiguration.StandardOperatorsDictionary)
+        .powerOfPrecedence(OperatorIfc.OPERATOR_PRECEDENCE_POWER)
+        .stripTrailingZeros(true)
+        .structuresAllowed(true)
+        .build();
+
+        Expression expression=new Expression("2.128 + a",configuration);
 ```
 
 ### Allow to Overwrite Constants
@@ -77,8 +77,13 @@ The default implementation is the _MapBasedFunctionDictionary_, which stores all
 
 ### Implicit Multiplication
 
-Implicit multiplication automatically adds in expression like "(a+b)(b+c)" the missing
-multiplication operator, so that the expression reads "(a+b) * (b+c)".
+Implicit multiplication automatically adds in expressions like "2x" or "(a+b)(b+c)" the missing
+multiplication operator, so that the expression reads "2*x" or "(a+b) * (b+c)".
+
+Implicit multiplication will not work for expressions like x(a+b), which will not be extended to "2*(a+b)".
+This expression is treated as a call to function "x", which, if not defined, will raise a parse exception.
+
+An expression like "2(a+b)" will be expanded to "2*(a+b)".
 
 By default, implicit multiplication is enabled. It can be disabled with this configuration
 parameter.
@@ -112,12 +117,12 @@ By default, EvalEx uses a lower precedence. You can configure to use a higher pr
 specifying it here, or by using a predefined constant:
 
 ```java
-ExpressionConfiguration configuration = ExpressionConfiguration.builder()
-    .powerOfPrecedence(OperatorIfc.OPERATOR_PRECEDENCE_POWER_HIGHER)
-    .build();
+ExpressionConfiguration configuration=ExpressionConfiguration.builder()
+        .powerOfPrecedence(OperatorIfc.OPERATOR_PRECEDENCE_POWER_HIGHER)
+        .build();
 
 // will now result in -4, instead of 4:
-Expression expression = new Expression("-2^2", configuration);
+        Expression expression=new Expression("-2^2",configuration);
 ```
 
 ### Strip Trailing Zeros

docs/index.md

@@ -27,7 +27,7 @@ changes._
 - Custom functions and operators can be added.
 - Functions can be defined with a variable number of arguments (see MIN, MAX and SUM functions).
 - Supports hexadecimal and scientific notations of numbers.
-- Supports implicit multiplication, e.g. (a+b)(a-b) or 2(x-y) which equals to (a+b)\*(a-b) or 2\*(
+- Supports implicit multiplication, e.g. 2x or (a+b)(a-b) or 2(x-y) which equals to (a+b)\*(a-b) or 2\*(
   x-y)
 - Lazy evaluation of function parameters (see the IF function) and support of sub-expressions.
 

src/main/java/com/ezylang/evalex/parser/Tokenizer.java

@@ -15,8 +15,7 @@
 */
 package com.ezylang.evalex.parser;
 
-import static com.ezylang.evalex.parser.Token.TokenType.BRACE_OPEN;
-import static com.ezylang.evalex.parser.Token.TokenType.INFIX_OPERATOR;
+import static com.ezylang.evalex.parser.Token.TokenType.*;
 
 import com.ezylang.evalex.config.ExpressionConfiguration;
 import com.ezylang.evalex.config.FunctionDictionaryIfc;
@@ -67,10 +66,14 @@ public Tokenizer(String expressionString, ExpressionConfiguration configuration)
   public List<Token> parse() throws ParseException {
     Token currentToken = getNextToken();
     while (currentToken != null) {
-      if (currentToken.getType() == BRACE_OPEN && implicitMultiplicationPossible()) {
+      if (implicitMultiplicationPossible(currentToken)) {
         if (configuration.isImplicitMultiplicationAllowed()) {
           Token multiplication =
-              new Token(currentToken.getStartPosition(), "*", TokenType.INFIX_OPERATOR);
+              new Token(
+                  currentToken.getStartPosition(),
+                  "*",
+                  TokenType.INFIX_OPERATOR,
+                  operatorDictionary.getInfixOperator("*"));
           tokens.add(multiplication);
         } else {
           throw new ParseException(currentToken, "Missing operator");
@@ -92,6 +95,19 @@ public List<Token> parse() throws ParseException {
     return tokens;
   }
 
+  private boolean implicitMultiplicationPossible(Token currentToken) {
+    Token previousToken = getPreviousToken();
+
+    if (previousToken == null) {
+      return false;
+    }
+
+    return ((previousToken.getType() == BRACE_CLOSE && currentToken.getType() == BRACE_OPEN)
+        || ((previousToken.getType() == NUMBER_LITERAL
+            && currentToken.getType() == VARIABLE_OR_CONSTANT))
+        || ((previousToken.getType() == NUMBER_LITERAL && currentToken.getType() == BRACE_OPEN)));
+  }
+
   private void validateToken(Token currentToken) throws ParseException {
     Token previousToken = getPreviousToken();
     if (previousToken != null
@@ -239,22 +255,6 @@ private Token parseOperator() throws ParseException {
         "Undefined operator '" + tokenString + "'");
   }
 
-  private boolean implicitMultiplicationPossible() {
-    Token previousToken = getPreviousToken();
-
-    if (previousToken == null) {
-      return false;
-    }
-
-    switch (previousToken.getType()) {
-      case BRACE_CLOSE:
-      case NUMBER_LITERAL:
-        return true;
-      default:
-        return false;
-    }
-  }
-
   private boolean arrayOpenOrStructureSeparatorNotAllowed() {
     Token previousToken = getPreviousToken();
 

src/test/java/com/ezylang/evalex/EvalEx2CompatibilityTest.java

@@ -22,6 +22,8 @@
 import java.math.BigDecimal;
 import java.math.MathContext;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 class EvalEx2CompatibilityTest {
 
@@ -217,6 +219,28 @@ void testSciNotation() throws EvaluationException, ParseException {
     assertThat(evaluateToNumber("2.2e-16 * 10.2")).isEqualByComparingTo("2.244E-15");
   }
 
+  @ParameterizedTest
+  @CsvSource(
+      delimiter = ':',
+      value = {
+        "2a*(a+b) : 20",
+        "2a*2b : 24",
+        "22(3+1) : 88",
+        "(1+2)(2-1) : 3",
+        "0xA(a+b) : 50",
+        "(a+b)(a-b) : -5"
+      })
+  void testImplicitMultiplication(String expressionString, String expectedResult)
+      throws EvaluationException, ParseException {
+    Expression expression =
+        new Expression(
+                expressionString,
+                ExpressionConfiguration.builder().mathContext(MathContext.DECIMAL32).build())
+            .with("a", 2)
+            .and("b", 3);
+    assertThat(expression.evaluate().getStringValue()).isEqualTo(expectedResult);
+  }
+
   private BigDecimal evaluateToNumber(String expression)
       throws EvaluationException, ParseException {
 

src/test/java/com/ezylang/evalex/parser/TokenizerImplicitMultiplicationTest.java

@@ -41,7 +41,7 @@ void testImplicitBraces() throws ParseException {
   }
 
   @Test
-  void testImplicitNumber() throws ParseException {
+  void testImplicitNumberBraces() throws ParseException {
     assertAllTokensParsedCorrectly(
         "2(x)",
         new Token(1, "2", TokenType.NUMBER_LITERAL),
@@ -51,6 +51,24 @@ void testImplicitNumber() throws ParseException {
         new Token(4, ")", TokenType.BRACE_CLOSE));
   }
 
+  @Test
+  void testImplicitNumberNoBraces() throws ParseException {
+    assertAllTokensParsedCorrectly(
+        "2x",
+        new Token(1, "2", TokenType.NUMBER_LITERAL),
+        new Token(2, "*", TokenType.INFIX_OPERATOR),
+        new Token(2, "x", TokenType.VARIABLE_OR_CONSTANT));
+  }
+
+  @Test
+  void testImplicitNumberVariable() throws ParseException {
+    assertAllTokensParsedCorrectly(
+        "2x",
+        new Token(1, "2", TokenType.NUMBER_LITERAL),
+        new Token(2, "*", TokenType.INFIX_OPERATOR),
+        new Token(2, "x", TokenType.VARIABLE_OR_CONSTANT));
+  }
+
   @Test
   void testImplicitMultiplicationNotAllowed() {
     ExpressionConfiguration config =