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use super::ast;
use super::builtins;
use super::builtins::BuiltinFunction;
use std::collections::HashMap;
use std::fmt;
use std::rc::Rc;
use std::sync::atomic::{AtomicUsize, Ordering};
#[derive(Debug, Clone)]
pub enum Value {
Integer(i64),
String(String),
Var(usize),
Function(usize, Rc<Value>),
BuiltinFunction(BuiltinFunction),
}
impl fmt::Display for Value {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
Value::Integer(value) => write!(f, "{} :: Integer", value),
Value::String(value) => write!(f, "{} :: String", value),
Value::Var(v) => write!(f, "{} :: Unbound variable", v),
Value::Function(_, _) => {
write!(f, "Function :: Function")
}
Value::BuiltinFunction(_) => write!(f, "Built-in function :: Function"),
}
}
}
static VAR_ID_INC: AtomicUsize = AtomicUsize::new(0);
fn advance_v() -> usize {
let v = VAR_ID_INC.load(Ordering::Relaxed);
VAR_ID_INC.store(v + 1, Ordering::Relaxed);
v
}
pub fn make_boolean_true_function() -> Value {
let x = advance_v();
let y = advance_v();
Value::Function(x, Rc::new(Value::Function(y, Rc::new(Value::Var(x)))))
}
pub fn make_boolean_false_function() -> Value {
let x = advance_v();
let y = advance_v();
Value::Function(x, Rc::new(Value::Function(y, Rc::new(Value::Var(y)))))
}
pub fn make_identity_function() -> Value {
let v = advance_v();
Value::Function(v, Rc::new(Value::Var(v)))
}
fn try_apply_function(func_rc: Rc<Value>, arg_rc: Rc<Value>, bound_v: Option<usize>) -> Rc<Value> {
let func = &*func_rc;
let arg = &*arg_rc;
match func {
Value::Function(func_v, body_rc) => {
let v1 = bound_v.unwrap_or(*func_v);
let body = &**body_rc;
match body {
Value::Var(v2) => {
if v1 == *v2 {
arg_rc
} else {
Rc::clone(body_rc)
}
}
Value::Function(body_v, _) => {
let new_body = try_apply_function(Rc::clone(body_rc), arg_rc, Some(v1));
Rc::new(Value::Function(*body_v, new_body))
}
_ => Rc::clone(body_rc),
}
}
Value::BuiltinFunction(builtin) => builtins::apply_builtin(builtin, arg),
_ => func_rc,
}
}
fn evaluate_expr_inner_unary(
symbol_table: &HashMap<String, Rc<Value>>,
inner: &ast::ExpressionInner,
) -> Rc<Value> {
match inner {
ast::ExpressionInner::IntegerLiteral(value) => Rc::new(Value::Integer(*value)),
ast::ExpressionInner::StringLiteral(value) => Rc::new(Value::String(value.clone())),
ast::ExpressionInner::Symbol(value) => {
let builtin_value = builtins::try_builtin_symbol_to_value(value);
if builtin_value.is_some() {
return Rc::new(builtin_value.unwrap());
}
let table_lookup_value = symbol_table.get(value);
if table_lookup_value.is_some() {
let lookup_rc = table_lookup_value.unwrap();
return Rc::clone(lookup_rc);
}
panic!("[runtime] symbol not defined: {:#?}", value);
}
ast::ExpressionInner::Expression(value_rc) => {
let sub_expr = &**value_rc;
evaluate_expr(symbol_table, sub_expr)
}
}
}
fn evaluate_expr_inner_binary(
symbol_table: &HashMap<String, Rc<Value>>,
lhs: &ast::ExpressionInner,
rhs: &ast::ExpressionInner,
) -> Rc<Value> {
match lhs {
ast::ExpressionInner::Expression(value_rc) => {
let sub_expr = &**value_rc;
let evaled_lhs = evaluate_expr(symbol_table, sub_expr);
let evaled_rhs = evaluate_expr_inner_unary(symbol_table, rhs);
try_apply_function(evaled_lhs, evaled_rhs, None)
}
ast::ExpressionInner::Symbol(value) => {
let lhs_value_rc: Rc<Value>;
if let Some(builtin) = builtins::try_builtin_symbol_to_value(value) {
lhs_value_rc = Rc::new(builtin);
} else if let Some(lookup) = symbol_table.get(value) {
lhs_value_rc = Rc::clone(lookup);
} else {
panic!("[runtime] symbol not defined: {:#?}", value);
}
let evaled_rhs = evaluate_expr_inner_unary(symbol_table, rhs);
try_apply_function(lhs_value_rc, evaled_rhs, None)
}
other => unreachable!(
"[runtime] this should not be on the left side of a binary expression: {:#?}",
other
),
}
}
fn evaluate_expr(
symbol_table: &HashMap<String, Rc<Value>>,
expression: &ast::Expression,
) -> Rc<Value> {
match expression {
ast::Expression::Unary(inner) => evaluate_expr_inner_unary(symbol_table, inner),
ast::Expression::Binary(inner1, inner2) => {
evaluate_expr_inner_binary(symbol_table, inner1, inner2)
}
}
}
pub fn evaluate(program: &ast::Program) {
let mut symbol_table: HashMap<String, Rc<Value>> = HashMap::new();
for statement in program {
match statement {
ast::Statement::Definition {
symbol,
parameters,
expression,
} => {
println!("[runtime] defining symbol: {:#?}", symbol);
let value = evaluate_expr(&symbol_table, expression);
symbol_table.insert(symbol.clone(), value);
}
ast::Statement::Expression(expression) => {
println!("[runtime] evaluating free-standing expression");
let value = evaluate_expr(&symbol_table, expression);
println!("Result: {}", value);
}
}
}
println!(
"[runtime] evaluation done, symbol_table state dump: {:#?}",
symbol_table
);
}
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