sybil/src/compile.rs

use crate::object::{QuoteTable, Value};
use crate::scope::*;
use crate::syn::ast::*;
use crate::vm::inst::*;
use std::rc::Rc;

pub struct Compile<'s> {
    scope_stack: &'s mut ScopeStack,
    quote_table: &'s mut QuoteTable,
}

impl<'s> Compile<'s> {
    pub fn new(scope_stack: &'s mut ScopeStack, quote_table: &'s mut QuoteTable) -> Self {
        Compile {
            scope_stack,
            quote_table,
        }
    }

    pub fn compile(&mut self, stmt_list: Vec<SpStmt>) -> Vec<SpInst> {
        // Compile meta-statements
        let expr_list = self.compile_meta(stmt_list);
        self.compile_expr_list(&expr_list)
    }

    /// Compile meta-expressions, like includes.
    fn compile_meta(&mut self, stmt_list: Vec<SpStmt>) -> Vec<SpExpr> {
        let mut expr_list = Vec::new();
        for stmt in stmt_list {
            match stmt.into_inner() {
                Stmt::Include(path) => {
                    let stmt_list = self.parse_include(&path);
                    expr_list.extend(self.compile_meta(stmt_list));
                }
                Stmt::Expr(expr) => expr_list.push(expr),
            }
        }
        expr_list
    }

    fn parse_include(&mut self, _path: &str) -> Vec<SpStmt> {
        todo!("includes")
    }

    fn compile_expr_list(&mut self, expr_list: &Vec<SpExpr>) -> Vec<SpInst> {
        // Scoping is done here.
        // Local scopes are implicit. If a variable is assigned to at
        // all in the current scope, it's considered to be a local.
        let mut code = Vec::new();
        for expr in expr_list {
            self.discover_locals(&expr);
            let thunk = self.compile_expr(&expr);
            code.extend(thunk.flatten());
        }
        code
    }

    fn compile_expr(&mut self, expr: &SpExpr) -> Thunk {
        match expr.inner() {
            Expr::Atom(atom) => self.compile_atom(atom),
            // this gets compiled whenever it gets evaluated
            Expr::Quote(stmts) => {
                self.scope_stack.push_scope();
                // TODO - is self.compile the right thing to do here?
                let compiled = Rc::new(self.compile(stmts.clone()));
                let locals = self.scope_stack.pop_scope().unwrap();
                let quote =
                    self.quote_table
                        .insert(expr.span().clone(), locals, stmts.clone(), compiled);
                let inst = Inst::PushValue(Value::Quote(quote));
                SpInst::new(expr.span().clone(), inst).into()
            }
        }
    }

    fn compile_atom(&mut self, atom: &SpAtom) -> Thunk {
        let inst = match atom.inner() {
            Atom::Float(f) => Inst::PushValue(Value::Float(*f)),
            Atom::Int(i) => Inst::PushValue(Value::Int(*i)),
            Atom::Str(s) => Inst::PushValue(Value::Str(s.clone())),
            Atom::Assign(text) => {
                let word = self.scope_stack.insert_local(text);
                Inst::Store(word)
            }
            Atom::Word(text) => {
                // Look for locally defined symbols first. One can't be found,
                // then create a local variable. The local variable *should* be
                // defined already, but sometimes things happen.
                let word = if let Some(word) = self.scope_stack.lookup_scoped(text) {
                    word
                } else {
                    self.scope_stack.insert_local(text)
                };
                Inst::Load(word)
            }
            Atom::Apply => Inst::Call,
        };
        SpInst::new(atom.span().clone(), inst).into()
    }

    /// Discovers and inserts local variables into the scope.
    ///
    /// If any assignment for a local variable appears in the scope, it will be
    /// inserted.
    fn discover_locals(&mut self, expr: &SpExpr) {
        if let Expr::Atom(atom) = expr.inner() {
            if let Atom::Assign(text) = atom.inner() {
                self.scope_stack.insert_local(text);
            }
        }
    }
}

#[derive(Debug, Clone)]
enum Thunk {
    Block(Vec<SpInst>),
    List(Vec<Thunk>),
}

impl From<SpInst> for Thunk {
    fn from(inst: SpInst) -> Thunk {
        Thunk::Block(vec![inst])
    }
}

impl Thunk {
    fn flatten(self) -> Vec<SpInst> {
        use Thunk::*;
        match self {
            Block(block) => block,
            List(list) => list.into_iter().flat_map(Thunk::flatten).collect(),
        }
    }
}