1 files changed, 27 insertions, 26 deletions
diff --git a/src/simple.rs b/src/simple.rs
index 8d87dbf..e763221 100644
--- a/src/simple.rs
+++ b/src/simple.rs
@@ -1,32 +1,33 @@
 use crate::ast::*;
 
-/// Evaluates an expression given a context (of variables) to a term, or fails.
-pub fn execute(context: &Context, expression: Expression) -> Result<Term, String> {
-    match expression {
-        Expression::Annotation { expr, .. } => execute(context, *expr),
-        Expression::Constant { term } => Ok(term),
-        Expression::Variable { id } => match context.get(&id) {
-            Some(term) => Ok(term.clone()),
-            None => Err(format!("no such variable in context {context:?}"))
-        },
-        Expression::Abstraction { param, func } =>
-            Err(format!("attempting to execute an abstraction ({}){}", param, func)),
-        Expression::Application { func, arg } => match *func {
-            Expression::Abstraction { param, func } => {
-                let value = execute(context, *arg)?;
-                let mut context = context.clone();
-                context.insert(param, value);
-                return execute(&context, *func);
-            }
-            _ => Err(format!("attempting to execute an application to non-abstraction {}", *func))
-        },
-        Expression::Conditional { if_cond, if_then, if_else } => {
-            match execute(context, *if_cond)? {
-                Term::Boolean(true) => execute(context, *if_then),
-                Term::Boolean(false) => execute(context, *if_else),
-                term => Err(format!("invalid type {} for a conditional", convert(&term)?))
+impl Context {
+    /// Evaluates an expression given a context (of variables) to a term, or fails.
+    pub fn execute(&self, expression: Expression) -> Result<Term> {
+        match expression {
+            Expression::Annotation { expr, .. } => self.execute(*expr),
+            Expression::Constant { term } => Ok(term),
+            Expression::Variable { id } => match self.get(&id) {
+                Some(term) => Ok(term.clone()),
+                None => Err(format!("no such variable in context {self:?}").into())
+            },
+            Expression::Abstraction { param, func } =>
+                Err(format!("attempting to execute an abstraction ({}){}", param, func).into()),
+            Expression::Application { func, arg } => match *func {
+                Expression::Abstraction { param, func } => {
+                    let value = self.execute(*arg)?;
+                    let mut context = self.clone();
+                    context.insert(param, value);
+                    return context.execute(*func);
+                }
+                _ => Err(format!("attempting to execute an application to non-abstraction {}", *func).into())
+            },
+            Expression::Conditional { if_cond, if_then, if_else } => {
+                match self.execute(*if_cond)? {
+                    Term::Boolean(true) => self.execute(*if_then),
+                    Term::Boolean(false) => self.execute(*if_else),
+                    term => Err(format!("invalid type {} for a conditional", &term.convert()?).into())
+                }
             }
         }
     }
 }
-