Evaluate basic arithmetic.

1 files changed, 46 insertions, 16 deletions

diff --git a/src/lib/eval/mod.rs b/src/lib/eval/mod.rs
index b582397..adee0e5 100644
--- a/src/lib/eval/mod.rs
+++ b/src/lib/eval/mod.rs
@@ -1,54 +1,84 @@
-use std::collections::HashMap;
 use super::types::Op;
 use super::types::Op::*;
-use super::types::SEXP;
-use super::types::SEXP::*;
-use super::types::Type::*;
+use super::sexpr::SExpr;
+use super::sexpr::SExpr::*;
+use super::types::Type;
 use super::types::Number;
+use super::environment::Environment;
 
 pub mod arith;
 
-pub type Env = HashMap<String, SEXP>;
-
-pub fn eval(expr: &SEXP, env: &mut Env) -> Result<SEXP, String> {
+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: &[SEXP], env: &mut Env) -> Result<SEXP, String> {
+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(Operator(x)) => *x,
-        Atom(Symbol(_s)) => return Err("Not yet implemented".to_string()),
+        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: &[SEXP], env: &mut Env) -> Result<SEXP, String> {
+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 op_add(expr: &[SEXP], env: &mut Env) -> Result<SEXP, String> {
-    let mut acc = Number(Number::Int(0));
+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 = (acc + b)?;
-        i += 1;
+        acc = (f(acc, b))?;
+        i += 1
     }
-    Ok(SEXP::Atom(acc))
+    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)
 }