xai-org/x-algorithm · error · SemanticCheckFailure

expecting the input to be of String or List type but…

Error message

expecting the input to be of String or List type but received: %s for %s

What it means

Slice()'s semantic validation requires the first argument's static typeBase to be Object, String, or List. Other types (Map, Set, Long, etc.) fail at build time with this message, which includes the offending type and the expression text.

Solutions

1. Convert to a List first (e.g. ToList/Set-to-list conversion) before slicing
2. Use ToSet+Contains or map accessors for Maps/Sets instead of Slice
3. Verify the first argument's return type is List or String

Example fix

// before
Slice(mySet, 0, 2)
// after
Slice(ToList(mySet), 0, 2)

// rule-language: convert before slicing
Slice(ToList(setVal), 0, 2)

// host code
Class<?> base = children.get(0).getReturnType().typeBase;
boolean ok = Object.class.equals(base) || String.class.equals(base) || List.class.equals(base);

When it happens

Trigger: Calling Slice(myMap, 0, 1), Slice(someSet, 0, 1), or Slice(42, 0, 1) at rule-build time.

Common situations: Assuming Slice works on any collection; refactoring input from List to Set/Map without updating the Slice call.

Related errors

• Contains expects input of String, Map, Set or Collection…
• Copy function only supports Map or StructTuple.
• Count expects input of String, Map or Collection types but
• Sort expects a collection of
• StructTuple field expects type , but received.

AI-assisted analysis of xai-org/x-algorithm@24c60942c5 (2026-08-28). Data as JSON: /api/errors/6ee5689deb932dc7. Report an issue: GitHub.

Appendix: source

Thrown at botmaker/src/java/com/twitter/botmaker/function/collection/Slice.java:68

    return SIGNATURE;
  }

  @Override
  protected CacheLevel getCacheLevel() {
    return CacheLevel.Global;
  }

  public Slice(String exprText, ImmutableList<ASTNode> children) throws SemanticCheckFailure {
    super(exprText, validateType(children));
  }

  private static ImmutableList<ASTNode> validateType(ImmutableList<ASTNode> children)
      throws SemanticCheckFailure {
    Class<?> inputType = children.get(0).getReturnType().typeBase;
    if (!Object.class.equals(inputType)
      && !String.class.equals(inputType)
      && !List.class.equals(inputType)) {
      throw new SemanticCheckFailure(mkErrorMessage(inputType));
    }
    return children;
  }

  @Override
  protected Object apply(
      Context<Runtime> context, Object input, Long beginIndex, Long endIndex) {
    if (input instanceof String) {
      return ((String) input).substring(beginIndex.intValue(), endIndex.intValue());
    } else if (input instanceof List) {
      return Collections.unmodifiableList(new ArrayList<>(
          ((List) input).subList(beginIndex.intValue(), endIndex.intValue())));
    } else {
      throw new IllegalArgumentException(mkErrorMessage(input.getClass()));
    }
  }

  @Override

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