From c7ff0b98146693b60a3f075818f96764f646b2d5 Mon Sep 17 00:00:00 2001
From: Rose Hogenson <rhogenson@posteo.net>
Date: Fri, 29 Jul 2022 22:41:17 -0700
Subject: Fix the bytecode interpreter.

I'm too scared to actually try to run it right now.
---
 bytecode/src/data.rs | 115 +++++++--------------------------------------------
 1 file changed, 14 insertions(+), 101 deletions(-)

(limited to 'bytecode/src/data.rs')

diff --git a/bytecode/src/data.rs b/bytecode/src/data.rs
index 4331f46..d6f9bd2 100644
--- a/bytecode/src/data.rs
+++ b/bytecode/src/data.rs
@@ -1,4 +1,7 @@
+use std::fmt;
+
 // The data representations of values of different types are given below.
+// - 0 represents an undefined value. Any operation with 0 will cause an error.
 // - Pointers are 64 bit unsigned (positive) ints which are
 //   word-aligned, i.e. 0 mod 8. All types not listed below are
 //   allocated on the heap behind a pointer.
@@ -18,12 +21,17 @@
 pub struct Pointer(pub usize);
 
 impl Pointer {
-    pub fn offset(self, i: i64) -> Self {
+    pub fn offset(self, i: usize) -> Self {
         let Pointer(u) = self;
-        if i > 0 {
-            return Pointer(u + usize::try_from(i).unwrap());
-        }
-        return Pointer(u - usize::try_from(-i).unwrap());
+        Pointer(u + i)
+    }
+}
+
+impl fmt::LowerHex for Pointer {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let val = self.0;
+
+        fmt::LowerHex::fmt(&val, f)
     }
 }
 
@@ -31,14 +39,9 @@ impl Pointer {
 pub struct Value(pub u64);
 
 impl Value {
-    pub fn is_nil(self) -> bool {
-        let Value(stack_representation) = self;
-        return stack_representation == 0;
-    }
-
     pub fn is_pointer(self) -> bool {
         let Value(stack_representation) = self;
-        return stack_representation & 0x7 == 0;
+        return stack_representation != 0 && stack_representation & 0x7 == 0;
     }
 
     pub fn from_pointer(p: Pointer) -> Self {
@@ -71,63 +74,18 @@ impl Value {
         return Ok(stack_representation as i64 >> 1);
     }
 
-    pub fn is_bool(self) -> bool {
-        let Value(stack_representation) = self;
-        return stack_representation == 0xa || stack_representation == 0x2;
-    }
-
     pub fn from_bool(b: bool) -> Self {
         if b {
             return Value(0xa);
         }
         return Value(0x2);
     }
-
-    pub fn to_bool(self) -> Result<bool, String> {
-        let Value(stack_representation) = self;
-        if !self.is_bool() {
-            return Err(format!("value {:x} is not a boolean", stack_representation));
-        }
-        return Ok(stack_representation == 0xa);
-    }
-
-    pub fn is_char(self) -> bool {
-        let Value(stack_representation) = self;
-        return stack_representation & 0x7 == 4;
-    }
-
-    pub fn from_char(c: char) -> Self {
-        return Value(u64::from(c) << 32 | 0x4);
-    }
-
-    pub fn to_char(self) -> Result<char, String> {
-        let Value(stack_representation) = self;
-        if !self.is_char() {
-            return Err(format!("value {:x} is not a char", stack_representation));
-        }
-        return Ok(
-            char::from_u32((stack_representation >> 32) as u32).ok_or(format!(
-                "value {:x} is not a valid char",
-                stack_representation >> 32
-            ))?,
-        );
-    }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
-    #[test]
-    fn is_nil() {
-        assert_eq!(true, Value(0).is_nil());
-    }
-
-    #[test]
-    fn is_not_nil() {
-        assert_eq!(false, Value(1).is_nil());
-    }
-
     #[test]
     fn is_pointer() {
         assert_eq!(true, Value(0xf8).is_pointer());
@@ -168,21 +126,6 @@ mod tests {
         assert_eq!(Ok(5), Value(0xb).to_int());
     }
 
-    #[test]
-    fn true_is_bool() {
-        assert_eq!(true, Value(0xa).is_bool());
-    }
-
-    #[test]
-    fn false_is_bool() {
-        assert_eq!(true, Value(2).is_bool());
-    }
-
-    #[test]
-    fn is_not_bool() {
-        assert_eq!(false, Value(0).is_bool());
-    }
-
     #[test]
     fn true_from_bool() {
         assert_eq!(Value(0xa), Value::from_bool(true));
@@ -192,34 +135,4 @@ mod tests {
     fn false_from_bool() {
         assert_eq!(Value(2), Value::from_bool(false));
     }
-
-    #[test]
-    fn true_to_bool() {
-        assert_eq!(Ok(true), Value(0xa).to_bool());
-    }
-
-    #[test]
-    fn false_to_bool() {
-        assert_eq!(Ok(false), Value(2).to_bool());
-    }
-
-    #[test]
-    fn is_char() {
-        assert_eq!(true, Value(0x6100000004).is_char());
-    }
-
-    #[test]
-    fn is_not_char() {
-        assert_eq!(false, Value(0).is_char());
-    }
-
-    #[test]
-    fn from_char() {
-        assert_eq!(Value(0x5800000004), Value::from_char('X'));
-    }
-
-    #[test]
-    fn to_char() {
-        assert_eq!(Ok('😂'), Value(0x1f60200000004).to_char());
-    }
 }
-- 
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