Doughlang/examples/7fold.rs

//! Demonstrates the visitor pattern

use std::{convert::Infallible, error::Error};

use doughlang::{
    ast::{
        fold::{Fold, Foldable},
        visit::{Visit, Walk},
        *,
    },
    lexer::Lexer,
    parser::{Parser, expr::Prec},
};

const CODE: &str = r#"
let x: [i32; 4] = [1, 2, 3, 4];

use foo::bar::baz::qux::{a, b, c, d, e};

struct<T> Point {x: T, y: T}

let v = Point {
    x, y: 20 + x
}

fn main() -> (&str, bool, i128) {
    // An if expression is like the ternary conditional operator in C
    let y = if 10 < 50 {
        "\u{1f988}"
    } else {
        "x"
    }
    
    // A `while` expression is like the while-else construct in Python,
    // but it returns a value via the `break` keyword
    let z = while false {
        // do a thing repeatedly
        break true
    } else {
        // If `while` does not `break`, fall through to the `else` expression
        false
    }

    // The same is true of `for` expressions!
    let w = for idx in 0..100 {
        if idx > 2 * 2 {
            break idx
        }
    } else 12345; // semicolon operator required here


    // desugars to
    let w = match ((0..100).into_iter()) {
        __iter => loop match (__iter.next()) {
            None => break 12345,
            Some (idx) => {
                if (idx > (2 * 2)) {
                    break idx
                }
            },
        },
    };

    // A block evaluates to its last expression,
    // or Empty if there is none
    // (🦈, false, 5)
    (y, z, w)
}

"#;

fn main() -> Result<(), Box<dyn Error>> {
    let ast: Anno<Expr> = Parser::new(Lexer::new(CODE)).parse(Prec::MIN)?;
    let mut counters = CountNodes::new();
    counters.visit(&ast);
    println!("{counters:#?}");

    let Ok(ast) = ast.fold_in(&mut Sevenfold) else {
        return Ok(());
    };
    println!("\nSevenfold:\n{ast}");

    Ok(())
}

#[derive(Clone, Debug, Default, PartialEq, Eq)]
struct CountNodes {
    exprs: usize,
    idents: usize,
    paths: usize,
    literals: usize,
    uses: usize,
    patterns: usize,
    binds: usize,
    makes: usize,
    makearms: usize,
}

impl CountNodes {
    fn new() -> Self {
        Self::default()
    }
}

impl<'a> Visit<'a> for CountNodes {
    type Error = Infallible;

    fn visit_expr<A: Annotation>(&mut self, expr: &'a Expr<A>) -> Result<(), Self::Error> {
        self.exprs += 1;
        expr.children(self)
    }

    fn visit_ident(&mut self, name: &'a str) -> Result<(), Self::Error> {
        self.idents += 1;
        name.children(self)
    }

    fn visit_path(&mut self, path: &'a Path) -> Result<(), Self::Error> {
        self.paths += 1;
        path.children(self)
    }

    fn visit_literal(&mut self, lit: &'a Literal) -> Result<(), Self::Error> {
        self.literals += 1;
        lit.children(self)
    }

    fn visit_use(&mut self, item: &'a Use) -> Result<(), Self::Error> {
        self.uses += 1;
        item.children(self)
    }

    fn visit_pat<A: Annotation>(&mut self, item: &'a Pat<A>) -> Result<(), Self::Error> {
        self.patterns += 1;
        item.children(self)
    }

    fn visit_bind<A: Annotation>(&mut self, item: &'a Bind<A>) -> Result<(), Self::Error> {
        self.binds += 1;
        item.children(self)
    }

    fn visit_make<A: Annotation>(&mut self, item: &'a Make<A>) -> Result<(), Self::Error> {
        self.makes += 1;
        item.children(self)
    }

    fn visit_makearm<A: Annotation>(&mut self, item: &'a MakeArm<A>) -> Result<(), Self::Error> {
        self.makearms += 1;
        item.children(self)
    }
}

struct Sevenfold;

impl<A: Annotation> Fold<A> for Sevenfold {
    type Error = ();

    fn fold_literal(&mut self, _lit: Literal) -> Result<Literal, Self::Error> {
        Ok(Literal::Int(7, 10))
    }
}