Display expected tokens on ParseError

src/main/java/edu/kit/typicalc/model/parser/LambdaParser.java

@@ -69,7 +69,7 @@ public class LambdaParser {
         TokenType current = token.getType();
         Optional<ParseError> error = nextToken();
         if (current != type) {
-            return Optional.of(ParseError.UNEXPECTED_TOKEN.withToken(lastToken));
+            return Optional.of(ParseError.UNEXPECTED_TOKEN.withToken(lastToken).expectedType(type));
         }
         return error;
     }
@@ -84,11 +84,15 @@ public class LambdaParser {
         if (t.isError()) {
             return t;
         }
+        Token last = token;
         Optional<ParseError> next = expect(TokenType.EOF);
         if (next.isEmpty()) {
             return t;
         }
-        return new Result<>(null, next.get());
+        return new Result<>(null,
+                (last.getType() == TokenType.EOF ? ParseError.TOO_FEW_TOKENS : ParseError.UNEXPECTED_TOKEN)
+                    .withToken(last)
+                    .expectedTypes(ATOM_START_TOKENS));
     }
 
     /**

src/main/java/edu/kit/typicalc/model/parser/ParseError.java

@@ -1,7 +1,11 @@
 package edu.kit.typicalc.model.parser;
 
+import java.util.Collection;
+import java.util.List;
+import java.util.Optional;
+
 /**
- * Errors that can occur when parsing a lambda term.
+ * Errors that can occur when parsing a lambda term or type assumption.
  *
  * @see LambdaLexer
  * @see LambdaParser
@@ -23,7 +27,8 @@ public enum ParseError {
      */
     UNEXPECTED_CHARACTER;
 
-    private Token cause = new Token(Token.TokenType.EOF, "", -1);
+    private Optional<Token> cause = Optional.empty();
+    private Optional<Collection<Token.TokenType>> needed = Optional.empty();
     private char wrongChar = '\0';
     private int position = -1;
 
@@ -34,7 +39,29 @@ public enum ParseError {
      * @return this object
      */
     public ParseError withToken(Token cause) {
-        this.cause = cause;
+        this.cause = Optional.of(cause);
+        return this;
+    }
+
+    /**
+     * Attach an expected token type to this error.
+     *
+     * @param needed the required token type
+     * @return this object
+     */
+    public ParseError expectedType(Token.TokenType needed) {
+        this.needed = Optional.of(List.of(needed));
+        return this;
+    }
+
+    /**
+     * Attach expected token types to this error.
+     *
+     * @param needed the possible token types
+     * @return this object
+     */
+    public ParseError expectedTypes(Collection<Token.TokenType> needed) {
+        this.needed = Optional.of(needed);
         return this;
     }
 
@@ -52,16 +79,29 @@ public enum ParseError {
     }
 
     /**
-     * @return the token associated with this error, or null if none
+     * @return the token associated with this error
      */
-    public Token getCause() {
+    public Optional<Token> getCause() {
         return cause;
     }
 
+    /**
+     * @return the expected/possible token(s) if this error is UNEXPECTED_TOKEN
+     */
+    public Optional<Collection<Token.TokenType>> getExpected() {
+        return needed;
+    }
+
+    /**
+     * @return the wrong character if this error is UNEXPECTED_CHARACTER ('\0' otherwise)
+     */
     public char getWrongCharacter() {
         return wrongChar;
     }
 
+    /**
+     * @return the character position if this error is UNEXPECTED_CHARACTER
+     */
     public int getPosition() {
         return position;
     }

src/main/java/edu/kit/typicalc/model/parser/Token.java

@@ -12,7 +12,7 @@ public class Token {
      * VARIABLE and NUMBER have a regular expression associated with them.
      * EOF is a special token to indicate that the end of file is reached.
      */
-    enum TokenType {
+    public enum TokenType {
         LAMBDA, // λ or a backslash
         VARIABLE, // [a-z][a-zA-Z0-9]* except "let" or "in" or constants
         LET, // let
@@ -25,7 +25,7 @@ public class Token {
         DOT, // .
         EQUALS, // =
         ARROW, // ->
-        EOF // pseudo token if end of file is reached
+        EOF // pseudo token if end of input is reached
     }
 
     /**

src/main/java/edu/kit/typicalc/view/TypicalcI18NProvider.java

@@ -38,16 +38,22 @@ public class TypicalcI18NProvider implements I18NProvider {
     public String getTranslation(String key, Locale locale, Object... params) {
         ResourceBundle bundle = ResourceBundle.getBundle(LANGUAGE_BUNDLE_PREFIX, locale);
 
+        String result;
         if (bundle.containsKey(key)) {
-            return bundle.getString(key);
+            result = bundle.getString(key);
         } else {
             try {
-                return this.generalBundle.getString(key);
+                result = this.generalBundle.getString(key);
             } catch (MissingResourceException exception) {
                 // this is only the case for untranslated texts
                 return "?[" + key + "]?";
             }
         }
+        // replace placeholders {0} ...
+        for (int i = 0; i < params.length; i++) {
+            result = result.replace(String.format("{%d}", i), params[i].toString());
+        }
+        return result;
     }
 
 }

src/main/java/edu/kit/typicalc/view/content/errorcontent/ErrorView.java

@@ -2,7 +2,6 @@ package edu.kit.typicalc.view.content.errorcontent;
 
 import com.vaadin.flow.component.Component;
 import com.vaadin.flow.component.dependency.CssImport;
-import com.vaadin.flow.component.details.Details;
 import com.vaadin.flow.component.html.Div;
 import com.vaadin.flow.component.html.H3;
 import com.vaadin.flow.component.html.Paragraph;
@@ -11,8 +10,12 @@ import com.vaadin.flow.component.orderedlayout.VerticalLayout;
 import com.vaadin.flow.i18n.LocaleChangeEvent;
 import com.vaadin.flow.i18n.LocaleChangeObserver;
 import edu.kit.typicalc.model.parser.ParseError;
+import edu.kit.typicalc.model.parser.Token;
 import edu.kit.typicalc.view.main.InfoContent;
 
+import java.util.Collection;
+import java.util.Optional;
+
 @CssImport("./styles/view/error-view.css")
 public class ErrorView extends VerticalLayout implements LocaleChangeObserver {
     private static final long serialVersionUID = 239587L;
@@ -21,8 +24,6 @@ public class ErrorView extends VerticalLayout implements LocaleChangeObserver {
     private static final String ADDITIONAL_INFO_ID = "errorAdditionalInfo";
     private static final String ERROR_SUMMARY_ID = "errorSummary";
 
-    private static final int NO_ADDITIONAL_INFO = -1;
-
     private final H3 heading;
     private final Div errorMessage;
     private final ParseError error;
@@ -44,9 +45,18 @@ public class ErrorView extends VerticalLayout implements LocaleChangeObserver {
         Paragraph summary = new Paragraph(getTranslation("root." + error.toString()));
         summary.setId(ERROR_SUMMARY_ID);
 
-        if (error == ParseError.TOO_FEW_TOKENS) {
+        switch (error) {
+            case TOO_FEW_TOKENS:
                 additionalInformation.add(new Span(getTranslation("root.tooFewTokensHelp")));
-        } else if (error == ParseError.UNEXPECTED_CHARACTER) {
+                break;
+            case UNEXPECTED_TOKEN:
+                Optional<Token> cause = error.getCause();
+                if (cause.isPresent()) {
+                    additionalInformation.add(new Span(getTranslation("root.wrongCharacter") + cause.get().getText()));
+                    additionalInformation.add(new Span(getTranslation("root.position") + cause.get().getPos()));
+                }
+                break;
+            case UNEXPECTED_CHARACTER:
                 char c = error.getWrongCharacter();
                 if (c != '\0') {
                     additionalInformation.add(new Span(getTranslation("root.wrongCharacter") + c));
@@ -54,16 +64,29 @@ public class ErrorView extends VerticalLayout implements LocaleChangeObserver {
                 } else {
                     return summary;
                 }
-        } else {
+                break;
-            if (error.getCause().getPos() == NO_ADDITIONAL_INFO) {
+            default:
-                return summary;
+                throw new IllegalStateException(); // delete when updating to Java 12+
-            } else {
-                additionalInformation.add(new Span(getTranslation("root.wrongCharacter") + error.getCause().getText()));
-                additionalInformation.add(new Span(getTranslation("root.position") + error.getCause().getPos()));
-            }
         }
 
-        return new Details(summary, additionalInformation);
+        // add expected tokens, if available
+        Optional<Collection<Token.TokenType>> expected = error.getExpected();
+        if (expected.isPresent()) {
+            Collection<Token.TokenType> possible = expected.get();
+            StringBuilder sb = new StringBuilder();
+            for (Token.TokenType t : possible) {
+                if (sb.length() > 0) {
+                    sb.append(' ');
+                    sb.append(getTranslation("root.or"));
+                    sb.append(' ');
+                }
+                sb.append(getTranslation("tokentype." + t));
+            }
+            additionalInformation.add(new Span(
+                    getTranslation("error.expectedToken", sb.toString())));
+        }
+
+        return new Div(summary, additionalInformation);
     }
 
     @Override

src/main/resources/language/translation_de.properties

@@ -100,6 +100,21 @@ root.UNEXPECTED_CHARACTER=Die Eingabe enthält ein Zeichen, welches an dieser St
 error.heading=Syntaktisch falsche Eingabe!
 root.wrongCharacter=Falsches Zeichen: \u0020
 root.position=An Position: \u0020
+error.expectedToken=Erwartet: {0}
+tokentype.LAMBDA=λ
+tokentype.VARIABLE=Variable
+tokentype.LET=let
+tokentype.IN=in
+tokentype.TRUE=true
+tokentype.FALSE=false
+tokentype.NUMBER=Zahl
+tokentype.LEFT_PARENTHESIS=(
+tokentype.RIGHT_PARENTHESIS=)
+tokentype.DOT=.
+tokentype.EQUALS==
+tokentype.ARROW=->
+tokentype.EOF=Ende der Eingabe
+root.or=oder
 root.slideExp=Typicalc ist eine Anwendung zur Visualisierung von Typinferenz. In der folgenden Slideshow wird ein \
 Beispielszenario mit den wichtigsten Funktionen der Website vorgeführt. Das relevante Bedienelement ist jeweils mit \
 einem roten Rahmen hervorgehoben. Zwischen einzelnen Slides kann mithilfe der Knöpfe am unteren Ende der Seite \

src/test/java/edu/kit/typicalc/model/parser/LambdaParserTest.java

@@ -98,7 +98,7 @@ class LambdaParserTest {
         parser = new LambdaParser("x)");
         ParseError error = parser.parse().unwrapError();
         assertEquals(ParseError.UNEXPECTED_TOKEN, error);
-        assertEquals(new Token(TokenType.RIGHT_PARENTHESIS, ")", 1), error.getCause());
+        assertEquals(new Token(TokenType.RIGHT_PARENTHESIS, ")", 1), error.getCause().get());
         parser = new LambdaParser("??");
         assertEquals(ParseError.UNEXPECTED_CHARACTER, parser.parse().unwrapError());
         parser = new LambdaParser("aλ");
@@ -110,39 +110,39 @@ class LambdaParserTest {
         parser = new LambdaParser("x 123333333333333");
         error = parser.parse().unwrapError();
         assertEquals(ParseError.UNEXPECTED_CHARACTER, error);
-        assertEquals(new Token(TokenType.NUMBER, "123333333333333", 2), error.getCause());
+        assertEquals(new Token(TokenType.NUMBER, "123333333333333", 2), error.getCause().get());
         parser = new LambdaParser("λ)");
         error = parser.parse().unwrapError();
         assertEquals(ParseError.UNEXPECTED_TOKEN, error);
-        assertEquals(new Token(TokenType.RIGHT_PARENTHESIS, ")", 1), error.getCause());
+        assertEquals(new Token(TokenType.RIGHT_PARENTHESIS, ")", 1), error.getCause().get());
         parser = new LambdaParser("λx=");
         error = parser.parse().unwrapError();
         assertEquals(ParseError.UNEXPECTED_TOKEN, error);
-        assertEquals(new Token(TokenType.EQUALS, "=", 2), error.getCause());
+        assertEquals(new Token(TokenType.EQUALS, "=", 2), error.getCause().get());
         parser = new LambdaParser("λx..");
         error = parser.parse().unwrapError();
         assertEquals(ParseError.UNEXPECTED_TOKEN, error);
-        assertEquals(new Token(TokenType.DOT, ".", 3), error.getCause());
+        assertEquals(new Token(TokenType.DOT, ".", 3), error.getCause().get());
         parser = new LambdaParser("let ) =");
         error = parser.parse().unwrapError();
         assertEquals(ParseError.UNEXPECTED_TOKEN, error);
-        assertEquals(new Token(TokenType.RIGHT_PARENTHESIS, ")", 4), error.getCause());
+        assertEquals(new Token(TokenType.RIGHT_PARENTHESIS, ")", 4), error.getCause().get());
         parser = new LambdaParser("let x .");
         error = parser.parse().unwrapError();
         assertEquals(ParseError.UNEXPECTED_TOKEN, error);
-        assertEquals(new Token(TokenType.DOT, ".", 6), error.getCause());
+        assertEquals(new Token(TokenType.DOT, ".", 6), error.getCause().get());
         parser = new LambdaParser("let x = )");
         error = parser.parse().unwrapError();
         assertEquals(ParseError.UNEXPECTED_TOKEN, error);
-        assertEquals(new Token(TokenType.RIGHT_PARENTHESIS, ")", 8), error.getCause());
+        assertEquals(new Token(TokenType.RIGHT_PARENTHESIS, ")", 8), error.getCause().get());
         parser = new LambdaParser("let x = y )");
         error = parser.parse().unwrapError();
         assertEquals(ParseError.UNEXPECTED_TOKEN, error);
-        assertEquals(new Token(TokenType.RIGHT_PARENTHESIS, ")", 10), error.getCause());
+        assertEquals(new Token(TokenType.RIGHT_PARENTHESIS, ")", 10), error.getCause().get());
         parser = new LambdaParser("let x = y in )");
         error = parser.parse().unwrapError();
         assertEquals(ParseError.UNEXPECTED_TOKEN, error);
-        assertEquals(new Token(TokenType.RIGHT_PARENTHESIS, ")", 13), error.getCause());
+        assertEquals(new Token(TokenType.RIGHT_PARENTHESIS, ")", 13), error.getCause().get());
     }
 
     @Test

src/test/java/edu/kit/typicalc/model/parser/TypeAssumptionParserTest.java

@@ -210,7 +210,7 @@ class TypeAssumptionParserTest {
             Result<Map<VarTerm, TypeAbstraction>, ParseError> type = parser.parse(Map.of("type1", entry.getKey()));
             assertTrue(type.isError());
             assertEquals(entry.getValue(), type.unwrapError());
-            if (entry.getValue().getCause().getPos() != -1) {
+            if (entry.getValue().getCause().isPresent()) {
                 assertEquals(entry.getValue().getCause(), type.unwrapError().getCause());
             }
         }