From 8705de9cc0956d42797cf1bcaa6de421bac5b3a8 Mon Sep 17 00:00:00 2001
From: Ivan Enderlin <ivan.enderlin@hoa-project.net>
Date: Thu, 26 Mar 2020 10:49:49 +0100
Subject: [PATCH] feat(interface-types) Simplify code by implementing
 `From<TryFromIntError>`.

---
 src/errors.rs                           | 11 +++++++++--
 src/interpreter/instructions/strings.rs | 24 ++++++++++--------------
 2 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/src/errors.rs b/src/errors.rs
index db6d7bd..bf9612a 100644
--- a/src/errors.rs
+++ b/src/errors.rs
@@ -5,6 +5,7 @@ use crate::{ast::InterfaceType, interpreter::Instruction};
 use std::{
     error::Error,
     fmt::{self, Display, Formatter},
+    num::TryFromIntError,
     result::Result,
     string::{self, ToString},
 };
@@ -150,7 +151,7 @@ pub enum InstructionErrorKind {
     /// The string contains invalid UTF-8 encoding.
     String(string::FromUtf8Error),
 
-    /// A negative value isn't allowed (like a negative pointer value).
+    /// Out of range integral type conversion attempted.
     NegativeValue {
         /// The variable name that triggered the error.
         subject: &'static str,
@@ -236,9 +237,15 @@ impl Display for InstructionErrorKind {
 
             Self::NegativeValue { subject } => write!(
                 formatter,
-                "read the value of `{}` which must be positive",
+                "attempted to convert `{}` but it appears to be a negative value",
                 subject
             ),
         }
     }
 }
+
+impl From<(TryFromIntError, &'static str)> for InstructionErrorKind {
+    fn from((_, subject): (TryFromIntError, &'static str)) -> Self {
+        InstructionErrorKind::NegativeValue { subject }
+    }
+}
diff --git a/src/interpreter/instructions/strings.rs b/src/interpreter/instructions/strings.rs
index 8a40ed2..66afa8d 100644
--- a/src/interpreter/instructions/strings.rs
+++ b/src/interpreter/instructions/strings.rs
@@ -33,18 +33,14 @@ executable_instruction!(
                     )
                 })?;
 
-            let pointer: usize = to_native::<i32>(&inputs[0], instruction)?.try_into().map_err(|_| {
-                InstructionError::new(
-                    instruction,
-                    InstructionErrorKind::NegativeValue { subject: "pointer" },
-                )
-            })?;
-            let length: usize = to_native::<i32>(&inputs[1], instruction)?.try_into().map_err(|_| {
-                InstructionError::new(
-                    instruction,
-                    InstructionErrorKind::NegativeValue { subject: "length" },
-                )
-            })?;
+            let pointer: usize = to_native::<i32>(&inputs[0], instruction)?
+                .try_into()
+                .map_err(|e| (e, "pointer").into())
+                .map_err(|k| InstructionError::new(instruction, k))?;
+            let length: usize = to_native::<i32>(&inputs[1], instruction)?
+                .try_into()
+                .map_err(|e| (e, "length").into())
+                .map_err(|k| InstructionError::new(instruction, k))?;
             let memory_view = memory.view();
 
             if length == 0 {
@@ -237,7 +233,7 @@ mod tests {
                 memory: Memory::new("Hello!".as_bytes().iter().map(|u| Cell::new(*u)).collect()),
                 ..Default::default()
             },
-            error: r#"`string.lift_memory` read the value of `pointer` which must be positive"#,
+            error: r#"`string.lift_memory` attempted to convert `pointer` but it appears to be a negative value"#,
     );
 
     test_executable_instruction!(
@@ -255,7 +251,7 @@ mod tests {
                 memory: Memory::new("Hello!".as_bytes().iter().map(|u| Cell::new(*u)).collect()),
                 ..Default::default()
             },
-            error: r#"`string.lift_memory` read the value of `length` which must be positive"#,
+            error: r#"`string.lift_memory` attempted to convert `length` but it appears to be a negative value"#,
     );
 
     test_executable_instruction!(