Circom: Syntax Error When Compiling Simple Circuit (Expecting ‘EOF’, ‘function’, ‘IDENTIFIER’)

If you’re reading this, chances are you’re facing a frustrating issue with Circom, a powerful tool for building and optimizing zk-SNARKs circuits. Specifically, you’re encountering a syntax error when compiling a simple circuit, with the error message expecting ‘EOF’, ‘function’, or ‘IDENTIFIER’. Fear not, dear developer, for we’re about to dive into the details and troubleshoot this issue together!

What is Circom?

Before we dive into the solution, let’s take a step back and briefly introduce Circom for those who might be new to the world of zk-SNARKs. Circom is a domain-specific language (DSL) designed to simplify the process of building and optimizing zk-SNARKs circuits. It provides a high-level, concise syntax for defining complex arithmetic circuits, making it an essential tool in the world of zero-knowledge proofs.

The Error Message: Expecting ‘EOF’, ‘function’, or ‘IDENTIFIER’

The error message you’re seeing is quite specific, and it’s essential to understand what it’s telling you. When Circom complains about expecting an ‘EOF’, ‘function’, or ‘IDENTIFIER’, it’s indicating that there’s a syntax error in your circuit definition. This error can occur due to various reasons, which we’ll explore in the next sections.

Before we dive into the solutions, let’s identify some common causes of this error:

• Missing or incorrect function declarations: Ensure that your function declarations are correctly formatted and situated within the circuit definition.
• Typographical errors: A single misplaced character or typo can throw off Circom’s parser. Double-check your code for any syntax errors.
• Invalid or unsupported syntax: Make sure you’re using the correct Circom syntax and not mixing it with other languages or syntax styles.
• Incorrect or missing imports: Verify that you’ve imported the necessary libraries and modules required for your circuit.

Solution 1: Check Your Function Declarations

Let’s start by examining your function declarations. In Circom, functions are defined using the `function` keyword, followed by the function name and parameters. Here’s an example of a correctly declared function:

function add(x, y) {
  return x + y;
}

Make sure your function declarations adhere to the following rules:

1. The `function` keyword should be followed by the function name.
2. The function name should be a valid identifier (i.e., it should not start with a number or special character).

If your function declaration looks correct, move on to the next solution.

Solution 2: Check for Typographical Errors

A single misplaced character or typo can cause Circom to stumble. Perform a thorough review of your code to catch any potential errors:

function add(x, y) {
  retrun x + y; // Typo: 'retrun' instead of 'return'
}

In this example, the typo in the `return` statement would cause the error. Carefully review your code, and don’t be afraid to use tools like syntax highlighting or code linters to help you spot errors.

Solution 3: Verify Correct Syntax and Imports

Ensure that you’re using the correct Circom syntax and not mixing it with other languages or syntax styles. Here’s an example of a correct Circom circuit definition:

template MyCircuit() {
  signal input x;
  signal input y;
  signal output[zk] result;

  component add = add(x, y);
  result <- add;
}

Also, verify that you’ve imported the necessary libraries and modules required for your circuit. For example, if you’re using the `zk` module, make sure you’ve imported it at the top of your Circom file:

import "zk.circom";

Solution 4: Use the Circom CLI to Debug

The Circom CLI provides a built-in debugger that can help you identify the source of the error. You can use the `circom` command with the `–debug` flag to enable debugging mode:

$ circom --debug my_circuit.circom

This will provide you with more detailed information about the error, including the line number and specific issue.

Conclusion

In this article, we’ve explored the common causes of the “Expecting ‘EOF’, ‘function’, or ‘IDENTIFIER'” error when compiling a simple Circom circuit. By following the solutions outlined above, you should be able to identify and fix the issue. Remember to carefully review your code, check your function declarations, and verify that you’re using the correct Circom syntax and imports.

Solution	Description
Check function declarations	Verify that function declarations are correctly formatted and situated
Check for typographical errors	Perform a thorough review of your code to catch any potential errors
Verify correct syntax and imports	Ensure that you’re using the correct Circom syntax and not mixing it with other languages
Use the Circom CLI to debug	Use the `circom` command with the `–debug` flag to enable debugging mode

By following these solutions and taking the time to carefully review your code, you should be able to resolve the “Expecting ‘EOF’, ‘function’, or ‘IDENTIFIER'” error and successfully compile your Circom circuit.

Remeber, in the world of zk-SNARKs, precision and attention to detail are crucial. Take your time, and don’t be afraid to ask for help if you’re still struggling with this error. Happy coding!

Frequently Asked Question

Get help with resolving the “Syntax Error When Compiling Simple Circuit” issue in Circom!