Refactoring, some pipes, exponents

idea.cxpr

@@ -3,7 +3,7 @@ let also_square(x) = x^2;
 
 let primes = range(100) |: filter(is_prime);
 let prime_squares = range(100) |: map(square);
-let also_prime_squares = range(100) |? is_prime |> square;
+let also_prime_squares = range(100) |? is_prime |: square;
 
 # 
 let primes_and_prime_squares = primes |& prime_squares;
@@ -27,6 +27,6 @@ for p : primes {
 
 let D = x -> {
     let facts = factors(x);
-    let product = facts |: foldl(1, mul);
+    let product = facts |> foldl(1, mul);
-    return facts |> (n -> product / n) |: foldl(0, add);
+    return facts |: (n -> product / n) |> foldl(0, add);
 }

src/bin/main.rs

@@ -25,6 +25,7 @@ fn panic_hook(info: &PanicInfo) {
 }
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
+    println!("{}", std::mem::size_of::<Value>());
     panic::set_hook(Box::new(panic_hook));
     let args: Vec<String> = std::env::args().collect();
     if args.len() == 2 {

src/eval.rs

@@ -1,6 +1,8 @@
 use std::{collections::HashMap, rc::Rc, cell::RefCell};
 
-use crate::{value::{Value, Complex, Func}, expr::{Stmt, Expr}, token::{TokenType, Token, OpType}, RuntimeError, Position};
+use num_traits::{Pow, Zero};
+
+use crate::{value::{Value, Complex, Func, Rational, CIterator}, expr::{Stmt, Expr}, token::{TokenType, Token, OpType}, RuntimeError, Position};
 
 #[derive(Debug)]
 pub struct Environment {
@@ -118,13 +120,13 @@ pub fn eval_stmt(stmt: &Stmt, env: EnvRef) -> Result<(), Unwind> {
             let name = unwrap_ident_token(var);
             let iter = eval_expr(expr, env.clone())?;
             env.borrow_mut().declare(name.clone(), Value::Nil);
-            let iterator = iter.iter(iter_pos);
+            let iterator = iter.iter();
             if let Err(e) = iterator {
-                return Err(RuntimeError::new(e, var.pos.clone()).into())
+                return Err(RuntimeError::new(e, iter_pos.clone()).into())
             }
             if let Ok(i) = iterator {
                 for v in i {
-                    let v = v?;
+                    let v = v.map_err(|e| e.complete(iter_pos.clone()))?;
                     let env = env.clone();
                     env.borrow_mut().set(name.clone(), v).expect("unreachable");
                     match eval_stmt(stmt, env) {
@@ -177,12 +179,14 @@ pub fn eval_expr(expr: &Expr, env: EnvRef) -> Result<Value, RuntimeError> {
         Expr::Binary { lhs, rhs, op } => match op.ty.get_op_type() {
             Some(OpType::Assignment) 
                 => eval_assignment(lhs, rhs, op, env),
-            Some(OpType::Additive) | Some(OpType::Multiplicative)
+            Some(OpType::Additive) | Some(OpType::Multiplicative) | Some(OpType::Exponential)
-                => eval_binary(lhs, rhs, op, env),
+                => eval_arith(lhs, rhs, op, env),
             Some(OpType::Boolean) 
                 => eval_boolean(lhs, rhs, op, env),
             Some(OpType::Comparison)
                 => eval_comp(lhs, rhs, op, env),
+            Some(OpType::Pipeline)
+                => eval_pipeline(lhs, rhs, op, env),
             o => todo!("{:?}", o) // TODO other operations
         },
         Expr::Unary { arg, op } => eval_unary(arg, op, env),
@@ -209,7 +213,7 @@ pub fn eval_expr(expr: &Expr, env: EnvRef) -> Result<Value, RuntimeError> {
                 let result = eval_expr(arg, env.clone())?;
                 arg_values.push(result);
             }
-            func.call(arg_values, pos)
+            func.call(arg_values).map_err(|e| e.complete(pos.clone()))
         },
         Expr::Index { lhs, index, pos } => {
             let l = eval_expr(lhs, env.clone())?;
@@ -308,7 +312,7 @@ pub fn eval_assignment(lhs: &Expr, rhs: &Expr, op: &Token, env: EnvRef) -> Resul
     }
 }
 
-pub fn eval_binary(lhs: &Expr, rhs: &Expr, op: &Token, env: EnvRef) -> Result<Value, RuntimeError> {
+pub fn eval_arith(lhs: &Expr, rhs: &Expr, op: &Token, env: EnvRef) -> Result<Value, RuntimeError> {
     let l = eval_expr(lhs, env.clone())?;
     let r = eval_expr(rhs, env)?;
     match op.ty {
@@ -317,6 +321,18 @@ pub fn eval_binary(lhs: &Expr, rhs: &Expr, op: &Token, env: EnvRef) -> Result<Va
         TokenType::Star => &l * &r,
         TokenType::Slash => &l / &r,
         TokenType::Percent => &l % &r,
+        TokenType::Caret => l.pow(&r),
+        TokenType::DoubleSlash => match (l, r) {
+            (Value::Int(_), Value::Int(b)) if b == 0 => Err("Integer division by zero".into()),
+            (Value::Rational(_), Value::Int(b)) if b == 0 => Err("Rational division by zero".into()),
+            (Value::Int(_), Value::Rational(b)) if b.is_zero() => Err("Rational division by zero".into()),
+            (Value::Rational(_), Value::Rational(b)) if b.is_zero() => Err("Rational division by zero".into()),
+            (Value::Int(a), Value::Int(b)) => Ok(Value::Rational(Rational::new(a, b))),
+            (Value::Rational(a), Value::Int(b)) => Ok(Value::from(a/b)),
+            (Value::Int(a), Value::Rational(b)) => Ok(Value::from(b.recip()*a)),
+            (Value::Rational(a), Value::Rational(b)) => Ok(Value::from(a/b)),
+            (x,y) => Err(format!("Unsupported operation 'fracdiv' between {:?} and {:?}", x, y))
+        },
         _ => todo!() // TODO other operations
     }.map_err(|e| RuntimeError::new(e, op.pos.clone()))
 }
@@ -367,6 +383,55 @@ pub fn eval_comp(lhs: &Expr, rhs: &Expr, op: &Token, env: EnvRef) -> Result<Valu
     }
 }
 
+fn pipecolon_inner(_: Vec<Value>, data: Rc<RefCell<Vec<Value>>>, iter_data: Rc<RefCell<Vec<CIterator>>>) -> Result<Value, RuntimeError> {
+    let f = &data.borrow()[0];
+    if let Some(next) = iter_data.borrow_mut()[0].next() {
+        f.call(vec![next?])
+    } else {
+        Ok(Value::Nil)
+    }
+}
+
+fn pipequestion_inner(_: Vec<Value>, data: Rc<RefCell<Vec<Value>>>, iter_data: Rc<RefCell<Vec<CIterator>>>) -> Result<Value, RuntimeError> {
+    let f = &data.borrow()[0];
+    loop {
+        let next = iter_data.borrow_mut()[0].next();
+        if let Some(next) = next {
+            let next = next?;
+            let success = f.call(vec![next.clone()])?.truthy();
+            if success {
+                return Ok(next)
+            }
+        } else {
+            return Ok(Value::Nil)
+        }
+    }
+}
+
+pub fn eval_pipeline(lhs: &Expr, rhs: &Expr, op: &Token, env: EnvRef) -> Result<Value, RuntimeError> {
+    let l = eval_expr(lhs, env.clone())?;
+    let r = eval_expr(rhs, env)?;
+    match op.ty {
+        TokenType::PipeColon => {
+            Ok(Value::Func(Func::BuiltinClosure {
+                arg_count: 0,
+                data: Rc::new(RefCell::new(vec![r])),
+                iter_data: Rc::new(RefCell::new(vec![l.iter()?])),
+                func: pipecolon_inner,
+            }))
+        },
+        TokenType::PipeQuestion => {
+            Ok(Value::Func(Func::BuiltinClosure {
+                arg_count: 0,
+                data: Rc::new(RefCell::new(vec![r])),
+                iter_data: Rc::new(RefCell::new(vec![l.iter()?])),
+                func: pipequestion_inner,
+            }))
+        },
+        _ => todo!()
+    }
+}
+
 pub fn eval_unary(arg: &Expr, op: &Token, env: EnvRef) -> Result<Value, RuntimeError> {
     let a = eval_expr(arg, env)?;
     match op.ty {

src/lib.rs

@@ -56,6 +56,13 @@ impl RuntimeError {
         }
     }
 
+    pub fn complete(mut self, last_pos: Position) -> Self {
+        if self.last_pos.is_none() {
+            self.last_pos = Some(last_pos);
+        }
+        self
+    }
+
     pub fn exit_fn(mut self, fn_name: Option<Rc<str>>, pos: Position) -> Self {
         self.stacktrace.push(Stackframe { pos: self.last_pos.expect("RuntimeError never completed after construction"), fn_name });
         self.last_pos = Some(pos);
@@ -69,6 +76,17 @@ impl RuntimeError {
     }
 }
 
+impl From<String> for RuntimeError {
+    fn from(s: String) -> Self {
+        Self::new_incomplete(s)
+    }
+}
+
+impl From<&str> for RuntimeError {
+    fn from(s: &str) -> Self {
+        Self::new_incomplete(s)
+    }
+}
 
 impl fmt::Display for ParserError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

src/parser.rs

@@ -45,19 +45,19 @@ impl Parser {
     pub fn parse(&mut self) -> Result<Vec<Stmt>, ParserError> {
         let mut stmts = vec![];
         while !self.at_end() {
-            stmts.push(self.statement()?);
+            stmts.push(self.statement(!self.repl)?);
         }
         Ok(stmts)
     }
 
-    fn statement(&mut self) -> Result<Stmt, ParserError> {
+    fn statement(&mut self, req_semicolon: bool) -> Result<Stmt, ParserError> {
         let next_ty = &self.peek().ty;
 
         match next_ty {
             TokenType::Let => {
                 // let statement
                 self.next();
-                self.letstmt()
+                self.letstmt(req_semicolon)
             },
             TokenType::LBrace => {
                 // block
@@ -81,16 +81,16 @@ impl Parser {
             },
             TokenType::Break => {
                 let tok = self.next();
-                self.terminate_stmt(Stmt::Break{ pos: tok.pos })
+                self.terminate_stmt(Stmt::Break{ pos: tok.pos }, req_semicolon)
             },
             TokenType::Continue => {
                 let tok = self.next();
-                self.terminate_stmt(Stmt::Continue{ pos: tok.pos })
+                self.terminate_stmt(Stmt::Continue{ pos: tok.pos }, req_semicolon)
             },
             TokenType::Return => {
                 let tok = self.next();
                 let expr = self.assignment()?;
-                self.terminate_stmt(Stmt::Return{ pos: tok.pos, expr })
+                self.terminate_stmt(Stmt::Return{ pos: tok.pos, expr }, req_semicolon)
             },
             TokenType::Fn => {
                 self.next();
@@ -99,18 +99,17 @@ impl Parser {
             _ => {
                 // fallback to an expression terminated with a semicolon
                 let expr = self.assignment()?;
-                self.terminate_stmt(Stmt::Expr{ expr })
+                self.terminate_stmt(Stmt::Expr{ expr }, req_semicolon)
             }
         }
     }
 
-    fn terminate_stmt(&mut self, stmt: Stmt) -> Result<Stmt, ParserError> {
+    fn terminate_stmt(&mut self, stmt: Stmt, req_semicolon: bool) -> Result<Stmt, ParserError> {
+        if !req_semicolon {
+            return Ok(stmt)
+        }
         if self.at_end() {
-            if self.repl {
+            self.err_on_eof()?;
-                return Ok(stmt)
-            } else {
-                self.err_on_eof()?;
-            }
         }
 
         let next = self.next();
@@ -122,39 +121,17 @@ impl Parser {
 
     }
 
-    fn letstmt(&mut self) -> Result<Stmt, ParserError> {
+    fn letstmt(&mut self, req_semicolon: bool) -> Result<Stmt, ParserError> {
         let expr = self.assignment()?;
         // must be followed by an assignment expression
         if let Expr::Binary{lhs, rhs, op: Token{ty: TokenType::Equal,..}} = expr {
             if let Expr::Ident{value: tok} = *lhs {
-                if self.at_end() {
+                self.terminate_stmt(Stmt::Let{lhs: tok, rhs: Some(*rhs)}, req_semicolon)
-                    if self.repl {
-                        return Ok(Stmt::Let{lhs: tok, rhs: Some(*rhs)})
-                    } else {
-                        self.err_on_eof()?;
-                    }
-                }
-                let next = self.next();
-                match next.ty {
-                    TokenType::Semicolon => Ok(Stmt::Let{lhs: tok, rhs: Some(*rhs)}),
-                    _ => Err(self.mk_error("Missing semicolon after 'let' statement".to_owned()))
-                }
             } else {
                 Err(self.mk_error("Invalid expression after 'let'".to_owned()))
             }
         } else if let Expr::Ident{value: tok} = expr {
-            if self.at_end() {
+            self.terminate_stmt(Stmt::Let{lhs: tok, rhs: None}, req_semicolon)
-                if self.repl {
-                    return Ok(Stmt::Let{lhs: tok, rhs: None})
-                } else {
-                    self.err_on_eof()?;
-                }
-            }
-            let next = self.next();
-            match next.ty {
-                TokenType::Semicolon => Ok(Stmt::Let{lhs: tok, rhs: None}),
-                _ => Err(self.mk_error("Missing semicolon after 'let' statement".to_owned()))
-            }
         } else {
             Err(self.mk_error("Invalid expression after 'let'".to_owned()))
         }
@@ -165,7 +142,7 @@ impl Parser {
         let mut ec = false;
         loop {
             let condition = self.assignment()?;
-            let body = self.statement()?;
+            let body = self.statement(true)?;
             if_clauses.push((condition, body));
             match self.peek().ty {
                 TokenType::Elif => { self.next(); continue },
@@ -174,7 +151,7 @@ impl Parser {
             }
         }
         let else_clause = if ec {
-            Some(Box::new(self.statement()?))
+            Some(Box::new(self.statement(true)?))
         } else {
             None
         };
@@ -195,7 +172,7 @@ impl Parser {
             self.err_on_eof()?;
             let expr = self.assignment()?;
             self.err_on_eof()?;
-            let stmt = self.statement()?;
+            let stmt = self.statement(true)?;
             Ok(Stmt::For{ var, expr, stmt: Box::new(stmt), iter_pos: colon.pos })
         } else {
             Err(self.mk_error("Expected identifier after for"))
@@ -206,7 +183,7 @@ impl Parser {
         self.err_on_eof()?;
         let expr = self.assignment()?;
         self.err_on_eof()?;
-        let stmt = self.statement()?;
+        let stmt = self.statement(true)?;
         Ok(Stmt::While{ expr, stmt: Box::new(stmt) })
     }
 
@@ -225,7 +202,7 @@ impl Parser {
         }
         let args = self.commalist(TokenType::RParen, Self::ident)?;
         self.err_on_eof()?;
-        let body = self.statement()?;
+        let body = self.statement(false)?;
         Ok(Stmt::Fn { name, args, body: Box::new(body) })
     }
 
@@ -240,7 +217,7 @@ impl Parser {
     fn block(&mut self) -> Result<Stmt, ParserError> {
         let mut stmts = vec![];
         while !self.at_end() && self.peek().ty != TokenType::RBrace {
-            stmts.push(self.statement()?)
+            stmts.push(self.statement(true)?)
         }
         self.err_on_eof()?;
         self.next();
@@ -411,7 +388,7 @@ impl Parser {
             }
             let args = self.commalist(TokenType::RParen, Self::ident)?;
             self.err_on_eof()?;
-            let body = self.statement()?;
+            let body = self.statement(false)?;
             Ok(Expr::Fn { args, body: Box::new(body) })
         } else {
             Err(self.mk_error(format!("Unexpected token: {:?}", next.ty)))

src/stdlib/mod.rs

@@ -1,8 +1,8 @@
-use std::{rc::Rc, io::Write, cmp::Ordering, time::{SystemTime, UNIX_EPOCH}};
+use std::{rc::Rc, io::Write, cmp::Ordering, time::{SystemTime, UNIX_EPOCH}, cell::RefCell};
 
 use num_traits::ToPrimitive;
 
-use crate::{value::{Value, Func}, eval::Environment};
+use crate::{value::{Value, Func, CIterator}, eval::Environment, RuntimeError};
 
 pub fn load(env: &mut Environment) {
     let mut name: Rc<str>;
@@ -32,28 +32,30 @@ pub fn load(env: &mut Environment) {
     env.declare(name.clone(), Value::Func(Func::Builtin { func: fn_im, arg_count: 1, name }));
     name = Rc::from("time"); 
     env.declare(name.clone(), Value::Func(Func::Builtin { func: fn_time, arg_count: 0, name }));
+    name = Rc::from("list"); 
+    env.declare(name.clone(), Value::Func(Func::Builtin { func: fn_list, arg_count: 1, name }));
 }
 
-fn fn_str(args: Vec<Value>) -> Result<Value, String> {
+fn fn_str(args: Vec<Value>) -> Result<Value, RuntimeError> {
     Ok(Value::String(args[0].to_string()))
 }
 
-fn fn_repr(args: Vec<Value>) -> Result<Value, String> {
+fn fn_repr(args: Vec<Value>) -> Result<Value, RuntimeError> {
     Ok(Value::String(args[0].repr()))
 }
 
-fn fn_print(args: Vec<Value>) -> Result<Value, String> {
+fn fn_print(args: Vec<Value>) -> Result<Value, RuntimeError> {
     print!("{}", args[0].to_string());
     std::io::stdout().flush().map_err(|e| e.to_string())?;
     Ok(Value::Nil)
 }
 
-fn fn_println(args: Vec<Value>) -> Result<Value, String> {
+fn fn_println(args: Vec<Value>) -> Result<Value, RuntimeError> {
     println!("{}", args[0].to_string());
     Ok(Value::Nil)
 }
 
-fn fn_input(_: Vec<Value>) -> Result<Value, String> {
+fn fn_input(_: Vec<Value>) -> Result<Value, RuntimeError> {
     let mut buffer = String::new();
     let stdin = std::io::stdin();
     stdin.read_line(&mut buffer).map_err(|e| e.to_string())?;
@@ -63,7 +65,7 @@ fn fn_input(_: Vec<Value>) -> Result<Value, String> {
     Ok(Value::from(buffer))
 }
 
-fn fn_ord(args: Vec<Value>) -> Result<Value, String> {
+fn fn_ord(args: Vec<Value>) -> Result<Value, RuntimeError> {
     if let Value::Char(c) = args[0] {
         Ok(Value::from(c as u32))
     } else {
@@ -71,7 +73,7 @@ fn fn_ord(args: Vec<Value>) -> Result<Value, String> {
     }
 }
 
-fn fn_chr(args: Vec<Value>) -> Result<Value, String> {
+fn fn_chr(args: Vec<Value>) -> Result<Value, RuntimeError> {
     if let Value::Int(i) = args[0] {
         if i >= 0 && i < (u32::MAX as i64) {
             if let Some(c) = char::from_u32(i as u32) {
@@ -84,57 +86,77 @@ fn fn_chr(args: Vec<Value>) -> Result<Value, String> {
     }
 }
 
-fn fn_range(args: Vec<Value>) -> Result<Value, String> {
+fn range_inner(_: Vec<Value>, data: Rc<RefCell<Vec<Value>>>, _: Rc<RefCell<Vec<CIterator>>>) -> Result<Value, RuntimeError> {
-    let min = &args[0];
+    const ZERO: Value = Value::Int(0);
-    let max = &args[1];
+    let mut d = data.borrow_mut();
-    match (min, max) {
+    if d[2] >= ZERO && d[0] >= d[1] {
+        Ok(Value::Nil)
+    } else if d[2] <= ZERO && d[0] <= d[1] {
+        Ok(Value::Nil)
+    } else {
+        let res = d[0].clone();
+        d[0] = (&d[0] + &d[2])?;
+        Ok(res)
+    }
+}
+
+fn fn_range(args: Vec<Value>) -> Result<Value, RuntimeError> {
+    let start = &args[0];
+    let end = &args[1];
+    let delta = match (start, end) {
         (Value::Int(a), Value::Int(b)) => match a.cmp(b) {
-            Ordering::Equal => Ok(Value::from(vec![])),
+            Ordering::Equal => 0,
-            Ordering::Less =>
+            Ordering::Less => 1,
-                Ok(Value::from((*a..*b).map(Value::Int).collect::<Vec<Value>>())),
+            Ordering::Greater => -1,
-            Ordering::Greater =>
-                Ok(Value::from(((*b+1)..(*a+1)).rev().map(Value::Int).collect::<Vec<Value>>()))
         },
-        _ => Err("Both arguments to range must be integers".into())
+        _ => return Err("Both arguments to range must be integers".into())
-    }
+    };
+    return Ok(Value::Func(Func::BuiltinClosure { 
+        arg_count: 0,
+        data: Rc::new(RefCell::new(vec![start.clone(), end.clone(), Value::Int(delta)])),
+        iter_data: Rc::new(RefCell::new(vec![])),
+        func: range_inner
+    }))
 }
 
-fn fn_len(args: Vec<Value>) -> Result<Value, String> {
+fn fn_len(args: Vec<Value>) -> Result<Value, RuntimeError> {
-    match &args[0] {
+    Ok(Value::Int(args[0].len().map_err(|e| RuntimeError::new_incomplete(e))? as i64))
-        Value::String(s) => Ok(Value::Int(s.len() as i64)),
-        Value::List(l) => Ok(Value::Int(l.borrow().len() as i64)),
-        Value::Map(m) => Ok(Value::Int(m.borrow().len() as i64)),
-        v => Err(format!("{:?} has no length", v))
-    }
 }
 
-fn fn_has(args: Vec<Value>) -> Result<Value, String> {
+fn fn_has(args: Vec<Value>) -> Result<Value, RuntimeError> {
     match &args[0] {
         Value::Map(m) => Ok(Value::from(m.borrow().contains_key(&args[1]))),
-        v => Err(format!("Argument to has must be a map, got {:?} ", v))
+        v => Err(format!("Argument to has must be a map, got {:?} ", v).into())
     }
 }
 
-fn fn_re(args: Vec<Value>) -> Result<Value, String> {
+fn fn_re(args: Vec<Value>) -> Result<Value, RuntimeError> {
     match &args[0] {
         Value::Int(x) => Ok(Value::Float(*x as f64)),
         Value::Float(x) => Ok(Value::Float(*x)),
         Value::Rational(x) => Ok(Value::Float(x.to_f64().unwrap())),
         Value::Complex(x) => Ok(Value::Float(x.re)),
-        x => Err(format!("Cannot get real part of {:?}", x))
+        x => Err(format!("Cannot get real part of {:?}", x).into())
     }
 }
 
-fn fn_im(args: Vec<Value>) -> Result<Value, String> {
+fn fn_im(args: Vec<Value>) -> Result<Value, RuntimeError> {
     match &args[0] {
         Value::Int(_) | Value::Float(_) | Value::Rational(_) 
             => Ok(Value::Float(0.0)),
         Value::Complex(x) => Ok(Value::Float(x.im)),
-        x => Err(format!("Cannot get real part of {:?}", x))
+        x => Err(format!("Cannot get real part of {:?}", x).into())
     }
 }
 
-fn fn_time(_: Vec<Value>) -> Result<Value, String> {
+fn fn_time(_: Vec<Value>) -> Result<Value, RuntimeError> {
     let time = SystemTime::now().duration_since(UNIX_EPOCH).map_err(|e| e.to_string())?;
     Ok(Value::from(time.as_secs_f64()))
 }
+
+fn fn_list(args: Vec<Value>) -> Result<Value, RuntimeError> {
+    let a = args[0].iter()?;
+    let mut res = Vec::new();
+    for v in a { res.push(v?); }
+    Ok(Value::from(res))
+}

src/value.rs

@@ -1,8 +1,8 @@
 use std::{rc::Rc, collections::HashMap, ops::*, fmt, cmp::Ordering, cell::RefCell, hash::Hash};
 
-use num_traits::{Zero, ToPrimitive};
+use num_traits::{Zero, ToPrimitive, Pow};
 
-use crate::{RuntimeError, Position, eval::{EnvRef, eval_stmt, Environment, Unwind}, expr::Stmt};
+use crate::{RuntimeError, eval::{EnvRef, eval_stmt, Environment, Unwind, eval_expr}, expr::Stmt};
 
 pub type Rational = num_rational::Ratio<i64>;
 pub type Complex = num_complex::Complex64;
@@ -13,12 +13,18 @@ pub enum Func {
         name: Option<Rc<str>>,
         args: Vec<Rc<str>>,
         env: EnvRef,
-        func: Stmt
+        func: Stmt,
     },
     Builtin {
         name: Rc<str>,
-        func: fn(Vec<Value>) -> Result<Value, String>,
+        func: fn(Vec<Value>) -> Result<Value, RuntimeError>,
-        arg_count: usize
+        arg_count: usize,
+    },
+    BuiltinClosure { 
+        func: fn(Vec<Value>, Rc<RefCell<Vec<Value>>>, Rc<RefCell<Vec<CIterator>>>) -> Result<Value, RuntimeError>,
+        data: Rc<RefCell<Vec<Value>>>,
+        iter_data: Rc<RefCell<Vec<CIterator>>>,
+        arg_count: usize,
     }
 }
 
@@ -35,6 +41,11 @@ impl fmt::Debug for Func {
                     .field("name", name)
                     .field("arg_count", arg_count)
                     .finish_non_exhaustive(),
+            Self::BuiltinClosure { arg_count, data, .. } 
+                => f.debug_struct("Func::BuiltinClosure") 
+                    .field("arg_count", arg_count)
+                    .field("data", data)
+                    .finish_non_exhaustive(),
         }
     }
     
@@ -44,34 +55,39 @@ impl Func {
     pub fn arg_count(&self) -> usize {
         match self {
             Self::Builtin { arg_count, .. } => *arg_count,
-            Self::Func { args, .. } => args.len()
+            Self::BuiltinClosure { arg_count, .. } => *arg_count,
+            Self::Func { args, .. } => args.len(),
         }
     }
 
-    pub fn call(&self, arg_values: Vec<Value>, pos: &Position) -> Result<Value, RuntimeError> {
+    pub fn call(&self, arg_values: Vec<Value>) -> Result<Value, RuntimeError> {
         match arg_values.len().cmp(&self.arg_count()) {
             Ordering::Equal => match self {
                 Self::Builtin { func, .. } 
-                    => func(arg_values).map_err(|e| RuntimeError::new(e, pos.clone())),
+                    => func(arg_values),
-                Self::Func { name, args, func, env } => {
+                Self::BuiltinClosure { func, data, iter_data, .. } 
+                    => func(arg_values, data.clone(), iter_data.clone()),
+                Self::Func { args, func, env, .. } => {
                     let mut env = Environment::extend(env.clone());
                     for (k, v) in args.iter().zip(arg_values.iter()) {
                         env.declare(k.clone(), v.clone());
                     }
-                    match eval_stmt(func, env.wrap()) {
+                    match func {
-                        Ok(()) => Ok(Value::Nil),
+                        Stmt::Expr { expr } => eval_expr(expr, env.wrap()),
-                        Err(Unwind::Return{ value, .. }) => Ok(value),
+                        stmt => match eval_stmt(stmt, env.wrap()) {
-                        Err(e) => Err(e.as_error().exit_fn(name.clone(), pos.clone()))
+                            Ok(()) => Ok(Value::Nil),
+                            Err(Unwind::Return{ value, .. }) => Ok(value),
+                            Err(e) => Err(e.as_error()),
+                        }
+
                     }
                 }
             }
-            Ordering::Less => Err(RuntimeError::new(
+            Ordering::Less => Err(RuntimeError::new_incomplete(
-                format!("Not enough arguments for function: expected {}, got {}", self.arg_count(), arg_values.len()), 
+                format!("Not enough arguments for function: expected {}, got {}", self.arg_count(), arg_values.len())
-                pos.clone() 
             )),
-            Ordering::Greater => Err(RuntimeError::new(
+            Ordering::Greater => Err(RuntimeError::new_incomplete(
-                format!("Too many arguments for function: expected {}, got {}", self.arg_count(), arg_values.len()), 
+                format!("Too many arguments for function: expected {}, got {}", self.arg_count(), arg_values.len())
-                pos.clone() 
             ))
         }
     }
@@ -88,53 +104,39 @@ impl Hash for Func {
             Self::Func { name, args, .. } => {
                 name.hash(state);
                 args.hash(state);
+            },
+            Self::BuiltinClosure { arg_count, data, .. } => {
+                arg_count.hash(state);
+                data.borrow().hash(state);
             }
         }
     }
 }
 
-pub enum EitherRteOrString {
+pub enum CIterator {
-    Rte(RuntimeError), String(String)
+    // precondition: value must be len()able
+    Indexable{ value: Value, idx: i64 },
+    Func(Func)
 }
 
-impl EitherRteOrString {
+impl Iterator for CIterator {
-    pub fn to_rte(self, pos: &Position) -> RuntimeError {
+    type Item = Result<Value, RuntimeError>;
-        match self {
-            Self::Rte(e) => e,
-            Self::String(s) => RuntimeError::new(s, pos.clone())
-        }
-    }
-}
 
-impl From<String> for EitherRteOrString {
-    fn from(s: String) -> Self {
-        Self::String(s)
-    }
-}
-
-impl From<RuntimeError> for EitherRteOrString {
-    fn from(e: RuntimeError) -> Self {
-        Self::Rte(e)
-    }
-}
-
-impl Iterator for Func {
-    type Item = Result<Value, EitherRteOrString>;
     fn next(&mut self) -> Option<Self::Item> {
         match self {
-            Self::Builtin { func, .. } => match (func)(vec![]) {
+            Self::Indexable{ value, ref mut idx } => {
-                Ok(Value::Nil) => None,
+                if *idx >= value.len().unwrap() as i64 {
-                r => Some(r.map_err(|e| e.into())),
+                    None
-            },
+                } else {
-            Self::Func { func, env, .. } => {
+                    let result = value.index(&Value::Int(*idx)).unwrap();
-                let env = Environment::extend(env.clone()).wrap();
+                    *idx += 1;
-                match eval_stmt(&func, env) {
+                    Some(Ok(result))
-                    Ok(_) => None,
-                    Err(Unwind::Return{ value: Value::Nil, .. }) => None,
-                    Err(Unwind::Return{ value, .. }) => Some(Ok(value)),
-                    Err(e) => Some(Err(e.as_error().into()))
                 }
-            }
+            },
+            Self::Func(f) => match f.call(vec![]) {
+                Ok(Value::Nil) => None,
+                x => Some(x)
+            },
         }
     }
 }
@@ -152,7 +154,6 @@ pub struct Type {
 }
 
 #[derive(Clone, Debug)]
-#[repr(u8)]
 pub enum Value {
     Nil,
     Type(usize),
@@ -177,19 +178,18 @@ impl Value {
             String(s) => !s.len() == 0,
             List(l) => !l.borrow().len() == 0,
             Map(m) => !m.borrow().len() == 0,
+            Char(c) => *c != '\0',
             _ => true
         }
     }
 
-    pub fn iter<'a>(&'a self, pos: &'a Position) -> Result<Box<dyn Iterator<Item=Result<Value, RuntimeError>> + '_>, String> {
+    pub fn iter<'a>(&'a self) -> Result<CIterator, String> {
         match self {
-            Value::String(s) 
+            Value::String(_) | Value::List(_)
-                => Ok(Box::new(s.chars()
+                => Ok(CIterator::Indexable { value: self.clone(), idx: 0 }),
-                    .map(Value::Char).map(Ok))),
-            Value::List(l) => Ok(Box::new(l.borrow().clone().into_iter().map(Ok))),
             Value::Func(f) => {
                 if f.arg_count() == 0 {
-                    Ok(Box::new(f.clone().map(|e| e.map_err(|e| e.to_rte(pos)))))
+                    Ok(CIterator::Func(f.clone()))
                 } else {
                     Err("Only zero-argument functions can be used as iterators".into())
                 }
@@ -198,11 +198,11 @@ impl Value {
         }
     }
 
-    pub fn call(&self, args: Vec<Value>, pos: &Position) -> Result<Value, RuntimeError> {
+    pub fn call(&self, args: Vec<Value>) -> Result<Value, RuntimeError> {
         if let Value::Func(f) = self {
-            f.call(args, pos)
+            f.call(args)
         } else {
-            Err(RuntimeError::new("Cannot call", pos.clone()))           
+            Err(RuntimeError::new_incomplete("Cannot call"))           
         }
     }
 
@@ -220,6 +220,7 @@ impl Value {
             Self::Map(m) => Rc::from(format!("{:?}", m)), // TODO fix
             Self::Type(_) => todo!(),
             Self::Func(Func::Builtin { name, func, .. }) => Rc::from(format!("<builtin fn {} at {:?}>", name, *func as *const ())),
+            Self::Func(Func::BuiltinClosure { func, .. }) => Rc::from(format!("<builtin anonymous fn at {:?}>", *func as *const ())),
             Self::Func(Func::Func { name, .. }) => match name {
                 Some(name) => Rc::from(format!("<fn {}>", name)),
                 None => Rc::from("<anonymous fn>"),
@@ -242,6 +243,7 @@ impl Value {
             Self::Map(m) => Rc::from(format!("{:?}", m)), // TODO fix
             Self::Type(_) => todo!(),
             Self::Func(Func::Builtin { name, func, .. }) => Rc::from(format!("<builtin fn {} at {:?}>", name, *func as *const ())),
+            Self::Func(Func::BuiltinClosure { func, .. }) => Rc::from(format!("<builtin anonymous fn at {:?}>", *func as *const ())),
             Self::Func(Func::Func { name, .. }) => match name {
                 Some(name) => Rc::from(format!("<fn {}>", name)),
                 None => Rc::from("<anonymous fn>"),
@@ -289,6 +291,15 @@ impl Value {
             v => Err(format!("Cannot assign to index in {:?}", v))
         }
     }
+
+    pub fn len(&self) -> Result<usize, String> {
+        match self {
+            Value::String(s) => Ok(s.len()),
+            Value::List(l) => Ok(l.borrow().len()),
+            Value::Map(m) => Ok(m.borrow().len()),
+            v => Err(format!("{:?} has no length", v).into())
+        }
+    }
 }
 
 impl PartialEq for Value {
@@ -449,9 +460,9 @@ macro_rules! impl_numeric_op {
             type Output = Result<Value, String>;
             fn $fnname(self, other: Self) -> Self::Output {
                 use Value::*;
-                use num_traits::ToPrimitive;
                 const RATIO_CAST_FAIL: &'static str = "Failed to cast Rational to Float";
                 match (self, other) {
+                    $($bonus)*
                     (Int(a),      Int(b))      => Ok(a.$fnname(b).into()),
                     (Rational(a), Int(b))      => Ok(a.$fnname(b).into()),
                     (Int(a),      Rational(b)) => Ok(self::Rational::from(*a).$fnname(b).into()),
@@ -468,7 +479,6 @@ macro_rules! impl_numeric_op {
                     (Rational(a), Complex(b))  => Ok(self::Complex::from(a.to_f64().ok_or(RATIO_CAST_FAIL)?).$fnname(b).into()),
                     (Complex(a),  Rational(b)) => Ok(a.$fnname(self::Complex::from(b.to_f64().ok_or(RATIO_CAST_FAIL)?)).into()),
                     (Complex(a),  Complex(b))  => Ok(a.$fnname(b).into()),
-                    $($bonus)*
                     (lhs, rhs) => Err(format!("Unsupported operation '{}' between {:?} and {:?}", stringify!($fnname), lhs, rhs))
                 }
             }
@@ -515,5 +525,51 @@ impl_numeric_op!(Mul, mul, {
     (List(a), Int(b)) | (Int(b), List(a))
         => Ok(Value::from(a.borrow().iter().cycle().take(a.borrow().len()*(*b as usize)).cloned().collect::<Vec<Value>>())),
 });
-impl_numeric_op!(Div, div, {});
+impl_numeric_op!(Div, div, {
-impl_numeric_op!(Rem, rem, {});
+    (Int(_), Int(b)) if *b == 0 => Err("Integer division by zero".into()),
+    (Rational(_), Int(b)) if *b == 0 => Err("Rational division by zero".into()),
+    (Int(_), Rational(b)) if b.is_zero() => Err("Rational division by zero".into()),
+    (Rational(_), Rational(b)) if b.is_zero() => Err("Rational division by zero".into()),
+});
+impl_numeric_op!(Rem, rem, {
+    (Int(_), Int(b)) if *b == 0 => Err("Integer modulo by zero".into()),
+    (Rational(_), Int(b)) if *b == 0 => Err("Rational modulo by zero".into()),
+    (Int(_), Rational(b)) if b.is_zero() => Err("Rational modulo by zero".into()),
+    (Rational(_), Rational(b)) if b.is_zero() => Err("Rational modulo by zero".into()),
+});
+
+impl Pow<&Value> for &Value {
+    type Output = Result<Value, String>;
+
+    fn pow(self, other: &Value) -> Self::Output {
+        use Value::*;
+        const RATIO_CAST_FAIL: &'static str = "Failed to convert rational to float";
+        match (self, other) {
+            (Int(a),      Int(b)) => match b {
+                x if *x < 0 => Err(format!("Cannot raise integer {:?} to negative integer exponent {:?}", a, b)),
+                x if *x > (u32::MAX as i64) => Err(format!("Integer exponent {:?} too large", x)),
+                _ => Ok(Value::from(a.pow(*b as u32)))
+            },
+            (Rational(a), Int(b))      => match b {
+                x if *x > (i32::MAX as i64) => Err(format!("Integer exponent {:?} too large", x)),
+                x if *x < (i32::MIN as i64) => Err(format!("Integer exponent {:?} too small", x)),
+                _ => Ok(Value::from(a.pow(*b as i32)))
+            },
+            (Int(_),      Rational(_)) => Err("Cannot raise integer to rational exponent".into()),
+            (Rational(_), Rational(_)) => Err("Cannot raise rational to rational exponent".into()),
+            (Float(a),    Int(b))      => Ok(a.pow(*b as f64).into()),
+            (Int(a),      Float(b))    => Ok((*a as f64).pow(b).into()),
+            (Float(a),    Rational(b)) => Ok(a.pow(b.to_f64().ok_or(RATIO_CAST_FAIL)?).into()),
+            (Rational(a), Float(b))    => Ok(a.to_f64().ok_or(RATIO_CAST_FAIL)?.pow(b).into()),
+            (Float(a),    Float(b))    => Ok(a.pow(b).into()),
+            (Int(a),      Complex(b))  => Ok(self::Complex::from(*a as f64).pow(b).into()),
+            (Complex(a),  Int(b))      => Ok(a.pow(self::Complex::from(*b as f64)).into()),
+            (Float(a),    Complex(b))  => Ok(self::Complex::from(a).pow(b).into()),
+            (Complex(a),  Float(b))    => Ok(a.pow(self::Complex::from(b)).into()),
+            (Rational(a), Complex(b))  => Ok(self::Complex::from(a.to_f64().ok_or(RATIO_CAST_FAIL)?).pow(b).into()),
+            (Complex(a),  Rational(b)) => Ok(a.pow(self::Complex::from(b.to_f64().ok_or(RATIO_CAST_FAIL)?)).into()),
+            (Complex(a),  Complex(b))  => Ok(a.pow(b).into()),
+            (lhs, rhs) => Err(format!("Unsupported operation 'pow' between {:?} and {:?}", lhs, rhs))
+        }
+    }
+}