use crate::parser::Datum;
use crate::parser::Datum::{Procedure, Symbol};
use crate::parser::make_symbol;
use crate::primitives;

type Mapping = (Datum, Datum);
type Frame = Vec<Mapping>;
pub type Env = Vec<Frame>;

pub fn get_global_environment() -> Env {
    vec![vec![(make_symbol("+"), Procedure(primitives::add)),
              (make_symbol("*"), Procedure(primitives::mul)),
              (make_symbol("-"), Procedure(primitives::sub))]]
}

pub fn lookup_variable_value(exp: &Datum, env: &Env) -> Datum {
    if let Symbol(symbol_name) = exp {
        for frame in env {
            for mapping in frame {
                if let (Symbol(current_name), datum) = mapping {
                    if symbol_name == current_name {
                        return datum.clone();
                    }
                }
            }
        }
    } else {
        panic!("LOOKUP-VARIABLE-VALUE -- not-a-symbol {:?}", exp)
    }
    panic!("LOOKUP-VARIABLE-VALUE -- unbound-variable-error {:?}", exp)
}