Reimplement Grammar to allow rich expressions

Author: vepo

src/main/antlr4/dev/vepo/jsonata/functions/generated/JSONataGrammar.g4

@@ -16,6 +16,7 @@ expression:
     | expression ARR_OPEN expression ARR_CLOSE                                # arrayQuery
     | expression rangePredicate                                               # rangeQuery
     | expression op=('<' | '<=' | '>' | '>=' | '!=' | '=' | 'in') expression  # booleanCompare
+    | expression '&' expression                                               # concatValues
     | '(' expression ')'                                                      # contextValue
     | STRING                                                                  # stringValue
     | NUMBER                                                                  # numberValue

src/main/java/dev/vepo/jsonata/functions/StringConcatJSONataFunction.java

@@ -1,19 +1,14 @@
 package dev.vepo.jsonata.functions;
 
 import static dev.vepo.jsonata.functions.json.JsonFactory.stringValue;
-import static java.util.stream.Collectors.joining;
-
-import java.util.List;
-import java.util.function.Function;
 
 import dev.vepo.jsonata.functions.data.Data;
 
-public record StringConcatJSONataFunction(List<Function<Data, Data>> sources) implements JSONataFunction {
+public record StringConcatJSONataFunction(JSONataFunction firstValue, JSONataFunction secondValue) implements JSONataFunction {
 
     @Override
     public Data map(Data original, Data current) {
-        return stringValue(sources.stream()
-                .map(fn -> fn.apply(current).toJson().asText())
-                .collect(joining()));
+        return stringValue(firstValue.map(original, current).toJson().asText() +
+                secondValue.map(original, current).toJson().asText());
     }
 }

src/main/java/dev/vepo/jsonata/parser/JSONataGrammarListener.java

@@ -16,21 +16,21 @@
 import dev.vepo.jsonata.functions.ArrayIndexJSONataFunction;
 import dev.vepo.jsonata.functions.ArrayQueryJSONataFunction;
 import dev.vepo.jsonata.functions.ArrayRangeJSONataFunction;
-import dev.vepo.jsonata.functions.BooleanCompareJSONataFunction;
-import dev.vepo.jsonata.functions.BooleanOperator;
 import dev.vepo.jsonata.functions.CompareOperator;
 import dev.vepo.jsonata.functions.CompareValuesJSONataFunction;
+import dev.vepo.jsonata.functions.ContextValueJSONataFunction;
 import dev.vepo.jsonata.functions.DeepFindByFieldNameJSONataFunction;
 import dev.vepo.jsonata.functions.FieldPathJSONataFunction;
-import dev.vepo.jsonata.functions.ContextValueJSONataFunction;
 import dev.vepo.jsonata.functions.JSONataFunction;
 import dev.vepo.jsonata.functions.JoinJSONataFunction;
+import dev.vepo.jsonata.functions.StringConcatJSONataFunction;
 import dev.vepo.jsonata.functions.WildcardJSONataFunction;
 import dev.vepo.jsonata.functions.generated.JSONataGrammarBaseListener;
 import dev.vepo.jsonata.functions.generated.JSONataGrammarParser.AllDescendantSearchContext;
 import dev.vepo.jsonata.functions.generated.JSONataGrammarParser.ArrayIndexQueryContext;
 import dev.vepo.jsonata.functions.generated.JSONataGrammarParser.ArrayQueryContext;
 import dev.vepo.jsonata.functions.generated.JSONataGrammarParser.BooleanCompareContext;
+import dev.vepo.jsonata.functions.generated.JSONataGrammarParser.ConcatValuesContext;
 import dev.vepo.jsonata.functions.generated.JSONataGrammarParser.ContextRefereceContext;
 import dev.vepo.jsonata.functions.generated.JSONataGrammarParser.ContextValueContext;
 import dev.vepo.jsonata.functions.generated.JSONataGrammarParser.ExpNumberValueContext;
@@ -206,7 +206,12 @@ public void exitToArray(ToArrayContext ctx) {
 
     @Override
     public void exitArrayIndexQuery(ArrayIndexQueryContext ctx) {
+        if (expressions.isEmpty()) {
             expressions.offer(new ArrayIndexJSONataFunction(Integer.valueOf(ctx.NUMBER().getText())));
+        } else {
+            var previousFunction = expressions.removeLast();
+            expressions.offer(new JoinJSONataFunction(previousFunction, new ArrayIndexJSONataFunction(Integer.valueOf(ctx.NUMBER().getText()))));
+        }
     }
 
     @Override
@@ -269,6 +274,13 @@ public void exitContextReferece(ContextRefereceContext ctx) {
         this.expressions.offer((original, value) -> original);
     }
 
+    @Override
+    public void exitConcatValues(ConcatValuesContext ctx) {
+        var currentFunction = expressions.removeLast();
+        var previousFunction = expressions.removeLast();
+        expressions.offer(new StringConcatJSONataFunction(previousFunction, currentFunction));
+    }
+
     // @Override
     // public void exitTransformerStringConcat(TransformerStringConcatContext ctx) {
     //     this.expressions.peekFirst()