From 6c5e3dea5d099c36e14442a28304062b3d7a2415 Mon Sep 17 00:00:00 2001
From: greg <greg.shuflin@protonmail.com>
Date: Sat, 12 May 2018 03:51:42 -0700
Subject: [PATCH] Assignment

---
 schala-lang/src/ast_reducing.rs | 15 +++++++++++++--
 schala-lang/src/eval.rs         | 31 +++++++++++++++++++++++++------
 2 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/schala-lang/src/ast_reducing.rs b/schala-lang/src/ast_reducing.rs
index 24ae03a..f57d130 100644
--- a/schala-lang/src/ast_reducing.rs
+++ b/schala-lang/src/ast_reducing.rs
@@ -26,6 +26,10 @@ pub enum Expr {
     f: Box<Expr>,
     args: Vec<Expr>,
   },
+  Assign {
+    val: Box<Expr>,
+    expr: Box<Expr>,
+  },
   UnimplementedSigilValue
 }
 
@@ -110,8 +114,15 @@ impl Declaration {
 
 impl BinOp {
   fn reduce(&self, lhs: &Box<Expression>, rhs: &Box<Expression>) -> Expr {
-    let f = Box::new(Expr::Func(Func::BuiltIn(self.sigil().clone())));
-    Expr::Call { f, args: vec![lhs.reduce(), rhs.reduce()]}
+    if **self.sigil() == "=" {
+      Expr::Assign {
+        val: Box::new(lhs.reduce()),
+        expr: Box::new(rhs.reduce()),
+      }
+    } else {
+      let f = Box::new(Expr::Func(Func::BuiltIn(self.sigil().clone())));
+      Expr::Call { f, args: vec![lhs.reduce(), rhs.reduce()]}
+    }
   }
 }
 
diff --git a/schala-lang/src/eval.rs b/schala-lang/src/eval.rs
index 812b5dc..2726fbc 100644
--- a/schala-lang/src/eval.rs
+++ b/schala-lang/src/eval.rs
@@ -345,6 +345,23 @@ impl<'a> State<'a> {
       },
       Val(v) => self.value(v),
       func @ Func(_) => Ok(func),
+      Assign { box val, box expr } => {
+        let name = match val  {
+          Expr::Val(name) => name,
+          _ => return Err(format!("Trying to assign to a non-value")),
+        };
+
+        let constant = match self.values.lookup(&name) {
+          None => return Err(format!("Runtime error: {} is undefined", name)),
+          Some(ValueEntry::Binding { constant, .. }) => constant.clone(),
+        };
+        if constant {
+          return Err(format!("Runtime error: trying to update {}, a non-mutable binding", name));
+        }
+        let val = self.expression(expr)?;
+        self.values.insert(name.clone(), ValueEntry::Binding { constant: false, val });
+        Ok(Expr::Unit)
+      },
       e => Err(format!("Expr {:?} eval not implemented", e))
     }
   }
@@ -402,8 +419,8 @@ impl<'a> State<'a> {
       ("+", &[Lit(Int(n))]) => Lit(Int(n)),
       ("+", &[Lit(Nat(n))]) => Lit(Nat(n)),
 
-      /* builtin functions */
 
+      /* builtin functions */
       ("print", &[ref anything]) => {
         print!("{}", anything.to_repl());
         Expr::Unit
@@ -417,7 +434,7 @@ impl<'a> State<'a> {
         io::stdin().read_line(&mut buf).expect("Error readling line in 'getline'");
         Lit(StringLit(Rc::new(buf)))
       },
-      _ => return Err(format!("Runtime error: bad or unimplemented builtin")),
+      (x, args) => return Err(format!("Runtime error: bad or unimplemented builtin {:?} | {:?}", x, args)),
     })
   }
 
@@ -431,8 +448,8 @@ impl<'a> State<'a> {
             Expr::Func(Func::UserDefined { name: Some(name.clone()), params: params.clone(), body: body.clone() }) //TODO here is unnecessary cloning
           } else {
             val.clone()
-          }),
-        _ => Err(format!("Functions not done")),
+          }
+        )
       }
     }
   }
@@ -448,13 +465,15 @@ mod eval_tests {
     ($string:expr, $correct:expr) => {
       let mut state = State::new();
       let all_output = state.evaluate(parse(tokenize($string)).0.unwrap().reduce(), true);
-      let ref output = all_output[0];
-      assert_eq!(*output, Ok($correct.to_string()));
+      let ref output = all_output.last().unwrap();
+      assert_eq!(**output, Ok($correct.to_string()));
     }
   }
 
   #[test]
   fn test_basic_eval() {
     fresh_env!("1 + 2", "3");
+    fresh_env!("var a = 1; a = 2", "Unit");
+    fresh_env!("var a = 1; a = 2; a", "2");
   }
 }