refactor(tazjin/rlox): Separate assignment and definition r/2034

So that:

> var a = 15;
> b = 12;
Error in program: Error { line: 0, kind: UndefinedVariable("b") }
> a = 12; print a;
Number(12.0)

Change-Id: I687e95ccc2d3084e39a71bd452656ae981c95191
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2300
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

1 files changed, 14 insertions, 1 deletions

diff --git a/users/tazjin/rlox/src/interpreter.rs b/users/tazjin/rlox/src/interpreter.rs
index 0855068b63..8d968a1f20 100644
--- a/users/tazjin/rlox/src/interpreter.rs
+++ b/users/tazjin/rlox/src/interpreter.rs
@@ -28,6 +28,19 @@ impl Environment {
                 kind: ErrorKind::UndefinedVariable(ident.into()),
             })
     }
+
+    fn assign(&mut self, name: &scanner::Token, value: Literal) -> Result<(), Error> {
+        let ident = identifier_str(name)?;
+        let target = self.values
+            .get_mut(ident)
+            .ok_or_else(|| Error {
+                line: name.line,
+                kind: ErrorKind::UndefinedVariable(ident.into()),
+            })?;
+
+        *target = value;
+        Ok(())
+    }
 }
 
 fn identifier_str<'a>(name: &'a scanner::Token) -> Result<&'a str, Error> {
@@ -156,7 +169,7 @@ impl Interpreter {
 
     fn eval_assign<'a>(&mut self, assign: &parser::Assign<'a>) -> Result<Literal, Error> {
         let value = self.eval(&assign.value)?;
-        self.globals.define(&assign.name, value.clone())?;
+        self.globals.assign(&assign.name, value.clone())?;
         Ok(value)
     }
 }