apple/pkl · error · VmException

missingMethodBody

missingMethodBody

Error message

missingMethodBody

What it means

Thrown when a function member has neither a body nor the `abstract` modifier. Pkl requires every non-abstract function to implement something; a bare signature is invalid syntax for a concrete function. Abstract functions without bodies are allowed and compile to CannotInvokeAbstractFunctionNode.

Source

Thrown at pkl-core/src/main/java/org/pkl/core/ast/builder/AstBuilder.java:2181

              throw exceptionBuilder()
                  .evalError("abstractMemberCannotHaveBody")
                  .withSourceSection(headerSection)
                  .build();
            }
            bodyNode = visitExpr(bodyContext);
          } else {
            if (VmModifier.isExternal(modifiers)) {
              bodyNode =
                  externalMemberRegistry.getFunctionBody(
                      scope.getQualifiedName(), headerSection, paramCount);
              if (bodyNode instanceof LanguageAwareNode languageAwareNode) {
                languageAwareNode.initLanguage(language);
              }
            } else if (VmModifier.isAbstract(modifiers)) {
              bodyNode =
                  new CannotInvokeAbstractFunctionNode(headerSection, scope.getQualifiedName());
            } else {
              throw exceptionBuilder()
                  .evalError("missingMethodBody", methodName)
                  .withSourceSection(headerSection)
                  .build();
            }
          }

          return new UnresolvedMethodNode(
              language,
              createSourceSection(entry),
              headerSection,
              scope.buildFrameDescriptor(),
              createDocSourceSection(entry.getDocComment()),
              annotations,
              modifiers,
              methodName,
              scope.getQualifiedName(),
              paramCount,
              typeParameters,

View on GitHub (pinned to f3efcbfc9b)

Solutions

1. Add a body: `function foo(): Int = 42`.
2. Or mark the member `abstract` if it must be implemented by subclasses.
3. Or remove the declaration entirely if it is unused.

Example fix

// before
function render(): String
// after
abstract function render(): String
// or
function render(): String = "default"

// every function member needs a body or the abstract modifier
function validateFunctionMember(m) {
  if (!m.isAbstract && m.body == null)
    throw new Error(`function ${m.name} needs a body or 'abstract'`);
}

When it happens

Trigger: Writing `function foo(): Int` (no `= expr`, no `abstract`) inside a class or module. Fires in the else branch of the body-handling logic where modifiers are not abstract and no bodyNode was produced.

Common situations: Porting Java interface-style declarations into Pkl and forgetting `abstract`; deleting a function body during refactoring; incomplete code generation or templated snippets left unimplemented.

Understand the failure class

Background: "NotImplementedError: Subclasses should override this method" / "must be implemented" — abstract method errors explained — this error's family across 40 libraries.

Related errors

• abstractMemberCannotHaveBody
• cannotDeclareTypeParameter
• duplicateTypeParameter
• invalidTypeName
• invalidConstObjectMemberModifier

AI-assisted analysis of apple/pkl@f3efcbfc9b (2026-09-08). Data as JSON: /api/errors/1e26e59419dc6191. Report an issue: GitHub.