langchain-rust 5.2.0

LangChain for Rust, the easiest way to write LLM-based programs in Rust
Documentation 
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use async_trait::async_trait;
use regex::Regex;

use super::{OutputParser, OutputParserError};

pub struct MarkdownParser {
    expresion: String,
    trim: bool,
}
impl MarkdownParser {
    pub fn new() -> Self {
        Self {
            expresion: r"```(?:\w+)?\s*([\s\S]+?)\s*```".to_string(),
            trim: false,
        }
    }

    pub fn with_custom_expresion(mut self, expresion: &str) -> Self {
        self.expresion = expresion.to_string();
        self
    }

    pub fn with_trim(mut self, trim: bool) -> Self {
        self.trim = trim;
        self
    }
}
impl Default for MarkdownParser {
    fn default() -> Self {
        Self::new()
    }
}

#[async_trait]
impl OutputParser for MarkdownParser {
    async fn parse(&self, output: &str) -> Result<String, OutputParserError> {
        let re = Regex::new(&self.expresion)?;
        if let Some(cap) = re.captures(output) {
            let find = cap[1].to_string();
            if self.trim {
                Ok(find.trim().to_string())
            } else {
                Ok(find)
            }
        } else {
            Err(OutputParserError::ParsingError(
                "No code block found".into(),
            ))
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[tokio::test]
    async fn test_markdown_parser_finds_code_block() {
        let parser = MarkdownParser::new();
        let markdown_content = r#"
```rust
fn main() {
    println!("Hello, world!");
}
```
"#;
        let result = parser.parse(markdown_content).await;
        println!("{:?}", result);

        let correct = r#"fn main() {
    println!("Hello, world!");
}"#;
        assert!(result.is_ok());
        assert_eq!(result.unwrap(), correct);
    }

    #[tokio::test]
    async fn markdown_parser_errors_and_custom_expression() {
        let err = MarkdownParser::new()
            .parse("no code here")
            .await
            .unwrap_err();
        assert!(matches!(err, OutputParserError::ParsingError(_)));

        let parser = MarkdownParser::new().with_custom_expresion(r"<json>([\s\S]+?)</json>");
        assert_eq!(
            parser.parse("x <json>{\"a\":1}</json> y").await.unwrap(),
            "{\"a\":1}"
        );

        let parser = MarkdownParser::new().with_custom_expresion("(");
        assert!(matches!(
            parser.parse("x").await.unwrap_err(),
            OutputParserError::RegexError(_)
        ));

        let parser = MarkdownParser::new()
            .with_custom_expresion(r"<a>([\s\S]+?)</a>")
            .with_trim(true);
        assert_eq!(parser.parse("<a>  v \n</a>").await.unwrap(), "v");
    }

    #[tokio::test]
    async fn simple_parser_trim() {
        use crate::output_parsers::SimpleParser;
        assert_eq!(SimpleParser::new().parse(" a ").await.unwrap(), " a ");
        assert_eq!(
            SimpleParser::default()
                .with_trim(true)
                .parse(" a \n")
                .await
                .unwrap(),
            "a"
        );
    }
}