fix g4 file

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

Author: xinyual

ppl/src/main/antlr/OpenSearchPPLParser.g4

@@ -431,8 +431,7 @@ 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
+   | lambda                                                                                     # lambdaExpr
    ;
 
 primaryExpression
@@ -559,10 +558,20 @@ functionArgs
    ;
 
 functionArg
-   : (ident EQUAL)? (valueExpression | comparisonExpression)
+   : (ident EQUAL)? functionArgExpression
    ;
 
 
+functionArgExpression
+   : lambda
+   | expression
+   ;
+
+lambda
+   : ident ARROW expression
+   | LT_PRTHS ident (COMMA ident)+ RT_PRTHS ARROW expression
+   ;
+
 relevanceArg
    : relevanceArgName EQUAL relevanceArgValue
    ;

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

@@ -507,7 +507,7 @@ 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.functionArgExpression())));
             });
     return new TableFunction(this.internalVisitExpression(ctx.qualifiedName()), builder.build());
   }