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use super::types::Op;
use super::types::Op::*;
use super::sexpr::SExpr;
use super::sexpr::SExpr::*;
use super::types::Type;
use super::types::Number;
use super::environment::Environment;
pub mod arith;
pub fn eval(expr: &SExpr, env: &mut Environment) -> Result<SExpr, String> {
match expr {
Atom(ref x) => Ok(Atom((*x).clone())),
Sexpr(ref s) => seval(s, env)
}
}
fn seval(sexpr: &[SExpr], env: &mut Environment) -> Result<SExpr, String> {
if sexpr.is_empty() {
return Err("Empty S Expression".to_string())
}
let op = match &sexpr[0] {
Atom(Type::Operator(x)) => *x,
Atom(Type::Symbol(_s)) => return Err("Not yet implemented".to_string()),
x => return Err(format!("{:?} is not a procedure", x))
};
op_eval(op, &sexpr[1..], env)
}
fn op_eval(op: Op, expr: &[SExpr], env: &mut Environment) -> Result<SExpr, String> {
match op {
Add => op_add(expr, env),
Sub => op_sub(expr, env),
Mul => op_mul(expr, env),
Div => op_div(expr, env),
//Define => define(expr, env),
_ => Err("Not yet implemented".to_string())
}
}
fn arith_op(
expr: &[SExpr],
env: &mut Environment,
identity: Number,
f: fn(Type, Type) -> Result<Type, String>) -> Result<SExpr, String>{
let mut acc = Type::Number(identity);
let mut i = 0;
if expr.len() > 1 {
let b = match eval(&expr[i], env)? {
Atom(x) => x,
Sexpr(_) => panic!("This should have evaluated to an atom")
};
acc = b;
i = 1;
}
while i < expr.len() {
let b = match eval(&expr[i], env)? {
Atom(x) => x,
Sexpr(_) => panic!("This should have evaluated to an atom")
};
acc = (f(acc, b))?;
i += 1
}
Ok(SExpr::Atom(acc))
}
fn op_add(expr: &[SExpr], env: &mut Environment) -> Result<SExpr, String> {
arith_op(expr, env, Number::Int(0), |a, b| a + b)
}
fn op_sub(expr: &[SExpr], env: &mut Environment) -> Result<SExpr, String> {
arith_op(expr, env, Number::Int(0), |a, b| a - b)
}
fn op_mul(expr: &[SExpr], env: &mut Environment) -> Result<SExpr, String> {
arith_op(expr, env, Number::Int(1), |a, b| a * b)
}
fn op_div(expr: &[SExpr], env: &mut Environment) -> Result<SExpr, String> {
arith_op(expr, env, Number::Float(1.0), |a, b| a / b)
}
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