Finished up to and including chapter 16

vm/src/error.rs

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+use itertools::Itertools;
+use rlox2_frontend::lexer::LexerError;
+use thiserror::Error;
+
+use crate::{Opcode, Value};
+
+#[derive(Error, Debug)]
+pub enum CompileError {}
+
+#[derive(Error, Debug)]
+pub enum RuntimeError {
+    #[error("Opcopde {opcode} had invalid operand {operand}")]
+    UnaryInvalidOperand { opcode: Opcode, operand: Value },
+    #[error("Opcopde {opcode} had invalid operands {left} and {right}")]
+    BinaryInvalidOperand { opcode: Opcode, left: Value, right: Value },
+    #[error("Division by zero")]
+    DivisionByZero,
+}
+
+#[derive(Error, Debug)]
+pub enum InterpretError {
+    #[error("{0}", format_multiple_errors(inner))]
+    LexerError { inner: Vec<LexerError> },
+    #[error("{inner}")]
+    CompileError { inner: CompileError },
+    #[error("{inner}")]
+    RuntimeError { inner: RuntimeError },
+    #[error("Called exit() with exit code {exit_code}")]
+    Exit { exit_code: i32 },
+}
+
+impl From<Vec<LexerError>> for InterpretError {
+    fn from(lexer_errs: Vec<LexerError>) -> Self {
+        InterpretError::LexerError { inner: lexer_errs }
+    }
+}
+
+impl From<CompileError> for InterpretError {
+    fn from(compile_err: CompileError) -> Self {
+        InterpretError::CompileError { inner: compile_err }
+    }
+}
+
+impl From<RuntimeError> for InterpretError {
+    fn from(runtime_err: RuntimeError) -> Self {
+        InterpretError::RuntimeError { inner: runtime_err }
+    }
+}
+
+fn format_multiple_errors(errs: &Vec<impl std::error::Error>) -> String {
+    let msg = if errs.len() == 1 {
+        errs[0].to_string()
+    } else {
+        errs.iter().map(|err| err.to_string()).join("\n")
+    };
+
+    msg
+}