62 lines
1.8 KiB
Rust
62 lines
1.8 KiB
Rust
use std::collections::HashMap;
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use crate::{errors::InterpreterError, tokens::Token};
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use super::{InterpreterResult, Value};
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/// The execution environment.
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#[derive(Debug, Default)]
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pub struct Environment {
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enclosing: Option<Box<Environment>>,
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values: HashMap<String, Value>,
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}
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impl Environment {
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/// Create an environment enclosed in another.
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pub fn create_child(parent: Self) -> Self {
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Self {
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enclosing: Some(Box::new(parent)),
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values: HashMap::default(),
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}
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}
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/// Restore an environment's parent.
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pub fn restore_parent(self) -> Self {
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*self.enclosing.unwrap()
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}
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/// Define a new variable.
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pub fn define(&mut self, name: String, value: Value) {
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self.values.insert(name, value);
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}
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/// Get the value of a variable.
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pub fn get(&self, name: &Token) -> InterpreterResult {
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match self.values.get(&name.lexeme as &str) {
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None => match &self.enclosing {
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None => Err(InterpreterError::new(
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name,
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&format!("undefined variable '{}'", name.lexeme),
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)),
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Some(parent) => parent.get(name),
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},
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Some(value) => Ok(value.clone()),
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}
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}
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/// Assign a value to an existing variable.
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pub fn assign(&mut self, name: &Token, value: Value) -> InterpreterResult {
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if self.values.contains_key(&name.lexeme as &str) {
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self.values.insert(name.lexeme.clone(), value);
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Ok(Value::Nil)
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} else {
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match &mut self.enclosing {
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None => Err(InterpreterError::new(
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name,
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&format!("undefined variable '{}'", name.lexeme),
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)),
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Some(parent) => parent.assign(name, value),
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}
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}
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}
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}
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