yash_arith/
env.rs

1// This file is part of yash, an extended POSIX shell.
2// Copyright (C) 2022 WATANABE Yuki
3//
4// This program is free software: you can redistribute it and/or modify
5// it under the terms of the GNU General Public License as published by
6// the Free Software Foundation, either version 3 of the License, or
7// (at your option) any later version.
8//
9// This program is distributed in the hope that it will be useful,
10// but WITHOUT ANY WARRANTY; without even the implied warranty of
11// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12// GNU General Public License for more details.
13//
14// You should have received a copy of the GNU General Public License
15// along with this program.  If not, see <https://www.gnu.org/licenses/>.
16
17//! Variable environment
18
19use std::collections::{BTreeMap, HashMap};
20use std::convert::Infallible;
21use std::ops::Range;
22
23/// Interface for accessing variables during evaluation
24///
25/// This crate does not implement any mechanism for storing variables. The
26/// caller of [`eval`](crate::eval()) must provide an implementation of this
27/// trait, which is used to access variables that appear in the evaluated
28/// expression.
29pub trait Env {
30    /// Object returned on a variable access error
31    type GetVariableError;
32
33    /// Object returned on an assignment error
34    type AssignVariableError;
35
36    /// Returns the value of the specified variable.
37    ///
38    /// This function must return:
39    ///
40    /// - `Ok(Some(v))` if the variable is defined and has the value `v`,
41    /// - `Ok(None)` if the variable is not defined, or
42    /// - `Err(error)` if an error occurs.
43    fn get_variable(&self, name: &str) -> Result<Option<&str>, Self::GetVariableError>;
44
45    /// Assigns a new value to the specified variable.
46    ///
47    /// The `location` parameter is the index range to the evaluated expression
48    /// where the assignment appears.
49    fn assign_variable(
50        &mut self,
51        name: &str,
52        value: String,
53        location: Range<usize>,
54    ) -> Result<(), Self::AssignVariableError>;
55}
56
57impl Env for HashMap<String, String> {
58    type GetVariableError = Infallible;
59    type AssignVariableError = Infallible;
60
61    fn get_variable(&self, name: &str) -> Result<Option<&str>, Infallible> {
62        Ok(self.get(name).map(String::as_str))
63    }
64
65    fn assign_variable(
66        &mut self,
67        name: &str,
68        value: String,
69        _location: Range<usize>,
70    ) -> Result<(), Infallible> {
71        self.insert(name.to_owned(), value);
72        Ok(())
73    }
74}
75
76impl Env for BTreeMap<String, String> {
77    type GetVariableError = Infallible;
78    type AssignVariableError = Infallible;
79
80    fn get_variable(&self, name: &str) -> Result<Option<&str>, Infallible> {
81        Ok(self.get(name).map(String::as_str))
82    }
83
84    fn assign_variable(
85        &mut self,
86        name: &str,
87        value: String,
88        _location: Range<usize>,
89    ) -> Result<(), Infallible> {
90        self.insert(name.to_owned(), value);
91        Ok(())
92    }
93}
yash_arith/env.rs

yash_arith/
env.rs
