lox_one 0.1.0

A tree-walking interpreter for the Lox programming language.
Documentation 
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use crate::{
    ast::Stmt,
    callable::Callable,
    interpreter::{error::RuntimeResult, Interpreter},
    lox_value::LoxValue,
};

use std::fmt;

use parse_display::Display;

#[derive(Debug, Display, Clone)]
#[display("<fun {name}>")]
pub struct FunDecl {
    pub name: String,
    pub params: Vec<String>,
    pub body: Box<Stmt>,
}

pub type NativeFunction = fn(&mut Interpreter, &[LoxValue]) -> RuntimeResult<LoxValue>;

#[derive(Display, Clone)]
pub enum Function {
    #[display("<native fun {}>")]
    Native {
        name: String,
        arity: usize,
        callable: NativeFunction,
    },
    #[display("{0}")]
    User(FunDecl),
}

impl PartialEq for Function {
    fn eq(&self, other: &Self) -> bool {
        self.name() == other.name()
    }

    fn ne(&self, other: &Self) -> bool {
        self.name() != other.name()
    }
}

impl Function {
    pub fn new_native_fun(
        name: String,
        arity: usize,
        callable: fn(&mut Interpreter, &[LoxValue]) -> RuntimeResult<LoxValue>,
    ) -> Function {
        Function::Native {
            name,
            arity,
            callable,
        }
    }
    pub fn new_user_fun(decl: FunDecl) -> Function {
        Function::User(decl)
    }
}

impl Callable for Function {
    fn name(&self) -> String {
        use Function::*;

        match self {
            Native {
                name,
                arity: _,
                callable: _,
            } => name.to_owned(),
            User(decl) => decl.name.to_owned(),
        }
    }

    fn arity(&self) -> usize {
        use Function::*;

        match self {
            Native {
                name: _,
                arity,
                callable: _,
            } => arity.to_owned(),
            User(decl) => decl.params.len(),
        }
    }

    fn call(&self, interpreter: &mut Interpreter, args: &[LoxValue]) -> RuntimeResult<LoxValue> {
        use Function::*;

        match self {
            Native {
                name: _,
                arity: _,
                callable,
            } => callable(interpreter, args),
            User(decl) => {
                // Create new environment
                interpreter.environment.begin_scope();
                for (param, arg) in decl.params.iter().zip(args.into_iter().cloned()) {
                    interpreter.environment.define(param, arg);
                }

                let res = interpreter.execute(&decl.body, false, true)?;
                interpreter.environment.end_scope();

                if let Some(value) = res {
                    Ok(value)
                } else {
                    Ok(LoxValue::Nil)
                }
            }
        }
    }
}

impl fmt::Debug for Function {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        use Function::*;
        match self {
            Native {
                name,
                arity: _,
                callable: _,
            } => {
                write!(f, "<native fun {name}>")
            }
            User(decl) => {
                write!(f, "<user fun {}>", &decl.name)
            }
        }
    }
}