Motoko Syntax Errors: "unexpected token 'private'" and Type Definition Issues

Developers Motoko
1

Subject: Motoko Syntax Errors: “unexpected token ‘private’” and Type Definition Issues

Hi everyone,

I’m running into persistent Motoko syntax errors in my project, and after following all the usual advice, I still can’t resolve them. Here’s what’s happening:

Main Error:

unexpected token 'private', expected one of token or <phrase> sequence:
  <eof>
  seplist(<dec>,<semicolon>) (e.g. 'let x : Int = 0')

Context:

  • The error appears right after my type definitions at the top of my actor in main.mo.
  • I have several custom types, both variants and records, e.g.:
    type SearchRequest = {
    query: Text;
    scope: SearchScope;
    filters: ?SearchFilter;
    sortBy: ?SearchSortBy;
    pagination: ?PaginationParams
} // <--- I tried with and without a semicolon here
  • I’ve tried:
    • Adding/removing semicolons after every field and after the closing brace of record types.
    • Ensuring no semicolon after the last tag in variant types, but a semicolon after the closing brace.
    • Reordering and reformatting the type definitions.
  • No matter what I do, the parser always throws an error at the first private declaration after the types.

What am I missing?

  • Is there a subtle Motoko syntax rule I’m overlooking for type definitions inside an actor?
  • Could this be a tooling or compiler bug?
  • Any working example of a Motoko actor with multiple custom types (both variant and record) at the top would be super helpful!

Thanks in advance for any help or pointers!

2

This is most likely caused by a missing semi directly above the line number mentioned in the error message.

Motoko requires semicolons between all declarations (types, methods, classes, etc.). For instance:

actor {
  type SearchRequest = {
    ...
  }; // Required semicolon

  public func search(request : SearchRequest) : async ?Text {
    ...
  }; // Optional semicolon since it's at the end of the code block
};

When in doubt, you can add semicolons at the end of every declaration.

The error message is saying that there should be a semicolon before the unexpected private token, so you just need to add one to the declaration above the line/column mentioned in the error.

If this doesn’t work, feel free to send me the file as a DM or reply with the lines of code surrounding the error message.

I’ll also bring this up in an internal discussion to see if we can improve the errors for missing semicolons.

3

Thank its helped. But caught with a different problem “Unbound variable caller” Error in Motoko Actor - Tried Multiple Solutions

4

Are you using AI? It’s possible that the code is missing shared({ caller }) on the enclosing actor method, which can happen with LLM-generated Motoko programs.

Example:

public shared({ caller }) func example() : async Principal {
  caller; // Return the caller
};

Here is the documentation for what you’re most likely looking for. Otherwise, I would need to see some code to be able to help further.

https://internetcomputer.org/docs/motoko/icp-features/caller-identification

5

Yes, I was using AI. Thanks for helping.