[Feature Request]: High cyclomatic complexity leds to bad readability

### Feature description

There are some functions that are highly complex and hard to read:

```
name cyclocomp
13 extract_occurrence 30
12 extract_dependency 13
33 move_functions_after_arrow 10
30 lang2calls 7
5 c.qenv 6
17 fix_shifted_comments 6
```

It would be good to make it easier to read the `extract_dependency` and `extract_occurrence` so that it is easier to modify them and fix any error.

### Code of Conduct

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### Contribution Guidelines

- [x] I agree to follow this project's Contribution Guidelines.

### Security Policy

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Find the R implementations and callers of extract_dependency and extract_occurrence, then read any existing tests around them. Refactor the functions to improve readability and reduce cyclomatic complexity while preserving their current behavior; verify the repository's existing checks pass.

Written by the indexing model from the issue text.