revert useless change

Signed-off-by: xinyual <xinyual@amazon.com>

Author: xinyual

ppl/src/main/antlr/OpenSearchPPLLexer.g4

@@ -385,13 +385,6 @@ JSON_DELETE:                        'JSON_DELETE';
 JSON_APPEND:                        'JSON_APPEND';
 JSON_EXTEND:                        'JSON_EXTEND';
 
-// LAMBDA FUNCTIONS
-//EXISTS:                             'EXISTS';
-FORALL:                             'FORALL';
-FILTER:                             'FILTER';
-TRANSFORM:                          'TRANSFORM';
-REDUCE:                             'REDUCE';
-
 // FLOWCONTROL FUNCTIONS
 IFNULL:                             'IFNULL';
 NULLIF:                             'NULLIF';

ppl/src/main/antlr/OpenSearchPPLParser.g4

@@ -462,8 +462,6 @@ valueExpression
    | timestampFunction                                                                          # timestampFunctionCall
    | LT_PRTHS valueExpression RT_PRTHS                                                          # parentheticValueExpr
    | LT_SQR_PRTHS subSearch RT_SQR_PRTHS                                                        # scalarSubqueryExpr
-   | ident ARROW expression                                                                     # lambda
-   | LT_PRTHS ident (COMMA ident)+ RT_PRTHS ARROW expression                                    # lambda
    ;
 
 primaryExpression
@@ -583,15 +581,14 @@ evalFunctionName
    | jsonFunctionName
    | geoipFunctionName
    | collectionFunctionName
-   | lambdaFunctionName
    ;
 
 functionArgs
    : (functionArg (COMMA functionArg)*)?
    ;
 
 functionArg
-   : (ident EQUAL)? valueExpression
+   : (ident EQUAL)? expression
    ;
 
 relevanceArg
@@ -720,14 +717,6 @@ jsonFunctionName
    | JSON_EXTEND
    ;
 
-lambdaFunctionName
-  : FORALL
-  | EXISTS
-  | FILTER
-  | TRANSFORM
-  | REDUCE
-  ;
-
 cryptographicFunctionName
    : MD5
    | SHA1

ppl/src/main/java/org/opensearch/sql/ppl/parser/AstBuilder.java

@@ -562,7 +562,7 @@ public UnresolvedPlan visitTableFunction(TableFunctionContext ctx) {
               String argName = (arg.ident() != null) ? arg.ident().getText() : null;
               builder.add(
                   new UnresolvedArgument(
-                      argName, this.internalVisitExpression(arg.valueExpression())));
+                      argName, this.internalVisitExpression(arg.expression())));
             });
     return new TableFunction(this.internalVisitExpression(ctx.qualifiedName()), builder.build());
   }

ppl/src/main/java/org/opensearch/sql/ppl/parser/AstExpressionBuilder.java

@@ -133,17 +133,6 @@ public UnresolvedExpression visitLogicalXor(LogicalXorContext ctx) {
     return new Xor(visit(ctx.left), visit(ctx.right));
   }
 
-  @Override
-  public UnresolvedExpression visitLambda(OpenSearchPPLParser.LambdaContext ctx) {
-
-    List<QualifiedName> arguments =
-        ctx.ident().stream()
-            .map(x -> this.visitIdentifiers(Collections.singletonList(x)))
-            .collect(Collectors.toList());
-    UnresolvedExpression function = visitExpression(ctx.expression());
-    return new LambdaFunction(function, arguments);
-  }
-
   /** Comparison expression. */
   @Override
   public UnresolvedExpression visitCompareExpr(CompareExprContext ctx) {