Revert "Use strings for errors."

This reverts commit 7b87d7185fc93b92606fcacbc1ea3d7a8e02cb20.

It was an interesting experiment, but String seems to be worse than
Box<dyn Error> in every way.

1 files changed, 24 insertions, 27 deletions

diff --git a/bytecode/src/main.rs b/bytecode/src/main.rs
index 4981734..4cba4ef 100644
--- a/bytecode/src/main.rs
+++ b/bytecode/src/main.rs
@@ -4,6 +4,7 @@ mod value;
 
 use encoding::{Arg, Op};
 use heap::Heap;
+use std::error::Error;
 use std::ffi::OsString;
 use std::io::{stderr, Write};
 use value::Value;
@@ -21,32 +22,29 @@ impl State {
         }
     }
 
-    fn op(&mut self, op: Op) -> Result<(), String> {
+    fn op(&mut self, op: Op) -> Result<(), Box<dyn Error>> {
         match op {
             Op::Alloc(op) => {
                 let Some(i) = self.read_arg(op.size).to_int() else {
-                    return Err(String::from("alloc needs an int"));
+                    return Err(Box::from("alloc needs an int"));
                 };
                 self.heap.locals[usize::from(op.out)] = Value::from_pointer(self.heap.alloc(i)?);
             }
             Op::Call => {
                 let Some(i) = self.heap.locals[0].to_int() else {
-                    return Err(String::from("call needs an int"));
+                    return Err(Box::from("call needs an int"));
                 };
-                let Ok(u) = usize::try_from(i) else {
-                    return Err(String::from("call needs a positive int"));
-                };
-                self.i = u;
+                self.i = usize::try_from(i)?;
             }
             Op::Poke(op) => {
                 let Some(p) = self.heap.locals[usize::from(op.ptr)].to_pointer() else {
-                    return Err(String::from("poke needs a pointer"));
+                    return Err(Box::from("poke needs a pointer"));
                 };
                 self.heap.poke(p + op.offset, self.read_arg(op.val))?;
             }
             Op::Peek(op) => {
                 let Some(p) = self.read_arg(op.val).to_pointer() else {
-                    return Err(String::from("peek needs a pointer"));
+                    return Err(Box::from("peek needs a pointer"));
                 };
                 self.heap.locals[usize::from(op.out)] = self.heap.peek(p + op.offset)?;
             }
@@ -61,66 +59,66 @@ impl State {
             }
             Op::Add(op) => {
                 let Some(v1) = self.read_arg(op.val1).to_int() else {
-                    return Err(String::from("add needs an int"));
+                    return Err(Box::from("add needs an int"));
                 };
                 let Some(v2) = self.read_arg(op.val2).to_int() else {
-                    return Err(String::from("add needs an int"));
+                    return Err(Box::from("add needs an int"));
                 };
                 self.heap.locals[usize::from(op.out)] = Value::from_int(v1.wrapping_add(v2));
             }
             Op::Sub(op) => {
                 let Some(v1) = self.read_arg(op.val1).to_int() else {
-                    return Err(String::from("sub needs an int"));
+                    return Err(Box::from("sub needs an int"));
                 };
                 let Some(v2) = self.read_arg(op.val2).to_int() else {
-                    return Err(String::from("sub needs an int"));
+                    return Err(Box::from("sub needs an int"));
                 };
                 self.heap.locals[usize::from(op.out)] = Value::from_int(v1.wrapping_sub(v2));
             }
             Op::Mul(op) => {
                 let Some(v1) = self.read_arg(op.val1).to_int() else {
-                    return Err(String::from("mul needs an int"));
+                    return Err(Box::from("mul needs an int"));
                 };
                 let Some(v2) = self.read_arg(op.val2).to_int() else {
-                    return Err(String::from("mul needs an int"));
+                    return Err(Box::from("mul needs an int"));
                 };
                 self.heap.locals[usize::from(op.out)] = Value::from_int(v1.wrapping_mul(v2));
             }
             Op::Div(op) => {
                 let Some(v1) = self.read_arg(op.val1).to_int() else {
-                    return Err(String::from("div needs an int"));
+                    return Err(Box::from("div needs an int"));
                 };
                 let Some(v2) = self.read_arg(op.val2).to_int() else {
-                    return Err(String::from("div needs an int"));
+                    return Err(Box::from("div needs an int"));
                 };
                 let Some(res) = v1.checked_div(v2) else {
-                    return Err(String::from("division by zero"));
+                    return Err(Box::from("division by zero"));
                 };
                 self.heap.locals[usize::from(op.out)] = Value::from_int(res);
             }
             Op::Less(op) => {
                 let Some(v1) = self.read_arg(op.val1).to_int() else {
-                    return Err(String::from("less needs an int"));
+                    return Err(Box::from("less needs an int"));
                 };
                 let Some(v2) = self.read_arg(op.val2).to_int() else {
-                    return Err(String::from("less needs an int"));
+                    return Err(Box::from("less needs an int"));
                 };
                 let res = if v1 < v2 { 1 } else { 0 };
                 self.heap.locals[usize::from(op.out)] = Value::from_int(res);
             }
             Op::Eq(op) => {
                 let Some(v1) = self.read_arg(op.val1).to_int() else {
-                    return Err(String::from("eq needs an int"));
+                    return Err(Box::from("eq needs an int"));
                 };
                 let Some(v2) = self.read_arg(op.val2).to_int() else {
-                    return Err(String::from("eq needs an int"));
+                    return Err(Box::from("eq needs an int"));
                 };
                 let res = if v1 == v2 { 1 } else { 0 };
                 self.heap.locals[usize::from(op.out)] = Value::from_int(res);
             }
             Op::If(op) => {
                 let Some(t) = self.read_arg(op.test).to_int() else {
-                    return Err(String::from("if needs an int"));
+                    return Err(Box::from("if needs an int"));
                 };
                 if t != 0 {
                     self.i = op.target;
@@ -131,13 +129,12 @@ impl State {
     }
 }
 
-fn run() -> Result<(), String> {
+fn run() -> Result<(), Box<dyn Error>> {
     let args: Vec<OsString> = std::env::args_os().collect();
     if args.len() != 2 {
-        return Err(String::from("usage: bytecode <file>"));
+        return Err(Box::from("usage: bytecode <file>"));
     }
-    let prog = std::fs::read(&args[1])
-        .map_err(|err| format!("read program from {:?}: {}", args[1], err))?;
+    let prog = std::fs::read(&args[1])?;
     let mut st = State {
         i: 0,
         heap: Heap::new(),