---
name: expression_verifier
description: Verify the syntax of an alpha expression irrespective of field existence. Use when checking if an alpha expression string is syntactically valid, has correct function arguments, and properly matched parentheses.
allowed-tools: Bash
---

# Expression Verifier

This skill verifies the syntax of a mathematical/logical expression using the project's `ExpressionValidator`.

It performs the following checks:
1. **Lexical Analysis**: Identifies valid tokens (operators, functions, variables).
2. **Syntax Analysis**: specific grammar rules.
3. **Function Validation**: checks argument counts and types for supported functions (e.g., `group_sum`, `rank`).
4. **Parenthesis Matching**.

**Note**: This skill **does not** validate whether the data fields (variables) mentioned in the expression actually exist in the database. It only checks if they are used as valid identifiers.

## How to use

To verify an expression, follow these steps:

1.  **Locate the Script**: The verification script is `scripts/verify_expr.py` inside this skill's folder. 
    *   **Context Check**: Because you (Claude) are running in the user's project directory, `scripts/` might not be in the current path.
    *   **Primary Path (Windows)**: Check `%USERPROFILE%\.claude\skills\expression_verifier\scripts\verify_expr.py` first.
    *   **Alternative**: If running as a project skill, check `.claude/skills/expression_verifier/scripts/verify_expr.py`.

2. **Execute**: Run the script using python. Ensure you quote the expression to handle spaces and special characters.

```bash
# Example (adjust path as needed)
python ".claude/skills/expression_verifier/scripts/verify_expr.py" "ts_rank(close, 10)"
```

## Interpreting Results

The script outputs a JSON object.
- If `valid` is `true`, the expression is syntactically correct.
- If `valid` is `false`, check the `errors` list for details.

## Examples

### Check a valid expression
```bash
python scripts/verify_expr.py "rank(close) / ts_delay(open, 5)"
```

### Check an invalid expression
```bash
python scripts/verify_expr.py "rank(close, 5)"  # rank only takes 1 argument usually
```