schala/schala-lang/src/tree_walk_eval/mod.rs

use std::{convert::From, fmt::Write};

use crate::{
    reduced_ir::{Callable, Expression, FunctionDefinition, Literal, ReducedIR},
    symbol_table::DefId,
    type_inference::{TypeContext, TypeId},
    util::ScopeStack,
};

mod evaluator;
mod test;

type EvalResult<T> = Result<T, RuntimeError>;

#[derive(Debug)]
pub struct State<'a> {
    environments: ScopeStack<'a, Memory, MemoryValue>,
}

//TODO - eh, I dunno, maybe it doesn't matter exactly how memory works in the tree-walking
//evaluator
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
enum Memory {
    Index(u32),
}

// This is for function param lookups, and is a hack
impl From<u8> for Memory {
    fn from(n: u8) -> Self {
        Memory::Index(4_000_000 + (n as u32))
    }
}

impl From<&DefId> for Memory {
    fn from(id: &DefId) -> Self {
        Self::Index(id.as_u32())
    }
}

#[derive(Debug)]
struct RuntimeError {
    msg: String,
}

impl From<String> for RuntimeError {
    fn from(msg: String) -> Self {
        Self { msg }
    }
}

impl From<&str> for RuntimeError {
    fn from(msg: &str) -> Self {
        Self { msg: msg.to_string() }
    }
}

impl RuntimeError {
    #[allow(dead_code)]
    fn get_msg(&self) -> String {
        format!("Runtime error: {}", self.msg)
    }
}

fn delim_wrapped(lhs: char, rhs: char, terms: impl Iterator<Item = String>) -> String {
    let mut buf = String::new();
    write!(buf, "{}", lhs).unwrap();
    for term in terms.map(Some).intersperse(None) {
        match term {
            Some(e) => write!(buf, "{}", e).unwrap(),
            None => write!(buf, ", ").unwrap(),
        };
    }
    write!(buf, "{}", rhs).unwrap();
    buf
}

/// Anything that can be stored in memory; that is, a function definition, or a fully-evaluated
/// program value.
#[derive(Debug)]
enum MemoryValue {
    Function(FunctionDefinition),
    Primitive(Primitive),
}

impl From<Primitive> for MemoryValue {
    fn from(prim: Primitive) -> Self {
        Self::Primitive(prim)
    }
}

#[derive(Debug)]
enum RuntimeValue {
    Expression(Expression),
    Evaluated(Primitive),
}

impl From<Expression> for RuntimeValue {
    fn from(expr: Expression) -> Self {
        Self::Expression(expr)
    }
}

impl From<Primitive> for RuntimeValue {
    fn from(prim: Primitive) -> Self {
        Self::Evaluated(prim)
    }
}

/// A fully-reduced value
#[derive(Debug, Clone)]
enum Primitive {
    Tuple(Vec<Primitive>),
    List(Vec<Primitive>),
    Literal(Literal),
    Callable(Callable),
    Object { type_id: TypeId, tag: u32, ordered_fields: Option<Vec<String>>, items: Vec<Primitive> },
}

impl Primitive {
    fn to_repl(&self, type_context: &TypeContext) -> String {
        match self {
            Primitive::Object { type_id, items, tag, ordered_fields: _ } if items.is_empty() =>
                type_context.variant_local_name(type_id, *tag).unwrap().to_string(),
            Primitive::Object { type_id, items, tag, ordered_fields: None } => {
                format!(
                    "{}{}",
                    type_context.variant_local_name(type_id, *tag).unwrap(),
                    delim_wrapped('(', ')', items.iter().map(|item| item.to_repl(type_context)))
                )
            }
            Primitive::Object { type_id, items, tag, ordered_fields: Some(fields) } => {
                let mut buf = format!("{} {{ ", type_context.variant_local_name(type_id, *tag).unwrap());
                for item in fields.iter().zip(items.iter()).map(Some).intersperse(None) {
                    match item {
                        Some((name, val)) => write!(buf, "{}: {}", name, val.to_repl(type_context)).unwrap(),
                        None => write!(buf, ", ").unwrap(),
                    }
                }
                write!(buf, " }}").unwrap();
                buf
            }
            Primitive::Literal(lit) => match lit {
                Literal::Nat(n) => format!("{}", n),
                Literal::Int(i) => format!("{}", i),
                Literal::Float(f) => format!("{}", f),
                Literal::Bool(b) => format!("{}", b),
                Literal::StringLit(s) => format!("\"{}\"", s),
            },
            Primitive::Tuple(terms) => delim_wrapped('(', ')', terms.iter().map(|x| x.to_repl(type_context))),
            Primitive::List(terms) => delim_wrapped('[', ']', terms.iter().map(|x| x.to_repl(type_context))),
            Primitive::Callable(..) => "<some-callable>".to_string(),
        }
    }

    fn unit() -> Self {
        Primitive::Tuple(vec![])
    }
}

impl From<Literal> for Primitive {
    fn from(lit: Literal) -> Self {
        Primitive::Literal(lit)
    }
}

impl<'a> State<'a> {
    pub fn new() -> Self {
        Self { environments: ScopeStack::new(Some("global".to_string())) }
    }

    pub fn evaluate(
        &mut self,
        reduced: ReducedIR,
        type_context: &TypeContext,
        repl: bool,
    ) -> Vec<Result<String, String>> {
        let mut evaluator = evaluator::Evaluator::new(self, type_context);
        evaluator.evaluate(reduced, repl)
    }
}