prql-compiler 0.7.1

PRQL is a modern language for transforming data — a simple, powerful, pipelined SQL replacement.
Documentation 
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use anyhow::Result;

use crate::ast::pl::Expr;
use crate::error::{Error, Reason};

pub trait ExactlyOneNode {
    fn exactly_one_node(self, who: &str, occupation: &str) -> Result<Expr, Error>;
}

impl ExactlyOneNode for Vec<Expr> {
    fn exactly_one_node(mut self, who: &str, occupation: &str) -> Result<Expr, Error> {
        match self.len() {
            1 => Ok(self.remove(0)),
            0 => Err(Error::new(Reason::Expected {
                who: Some(who.to_string()),
                expected: format!("only one {occupation}"),
                found: "none".to_string(),
            })),
            _ => Err(Error::new(Reason::Expected {
                who: Some(who.to_string()),
                expected: format!("only one {occupation}"),
                found: "more".to_string(),
            })
            .with_span(self[1].span)),
        }
    }
}