175 lines
6.2 KiB
Markdown
175 lines
6.2 KiB
Markdown
# evalexpr
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[](https://docs.rs/evalexpr)
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Evalexpr is a powerful arithmetic and boolean expression evaluator.
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## [Documentation](https://docs.rs/evalexpr)
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<!-- cargo-sync-readme start -->
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## Quickstart
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Add `evalexpr` as dependency to your `Cargo.toml`:
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```toml
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[dependencies]
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evalexpr = "0.5"
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```
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Add the `extern crate` definition to your `main.rs` or `lib.rs`:
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```rust
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extern crate evalexpr;
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```
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Then you can use `evalexpr` to evaluate expressions like this:
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```rust
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use evalexpr::*;
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assert_eq!(eval("1 + 2 + 3"), Ok(Value::from(6)));
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assert_eq!(eval("1 - 2 * 3"), Ok(Value::from(-5)));
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assert_eq!(eval("1.0 + 2 * 3"), Ok(Value::from(7.0)));
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assert_eq!(eval("true && 4 > 2"), Ok(Value::from(true)));
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```
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And you can use variables and functions in expressions like this:
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```rust
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use evalexpr::*;
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let mut configuration = HashMapConfiguration::new();
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configuration.insert_variable("five", 5);
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configuration.insert_variable("twelve", 12);
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configuration.insert_function("f", Function::new(1 /* argument amount */, Box::new(|arguments| {
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if let Value::Int(int) = arguments[0] {
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Ok(Value::Int(int / 2))
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} else if let Value::Float(float) = arguments[0] {
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Ok(Value::Float(float / 2.0))
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} else {
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Err(Error::expected_number(arguments[0].clone()))
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}
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})));
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assert_eq!(eval_with_configuration("five + 8 > f(twelve)", &configuration), Ok(Value::from(true)));
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```
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You can also precompile expressions like this:
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```rust
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use evalexpr::*;
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let precompiled = build_operator_tree("a * b - c > 5").unwrap();
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let mut configuration = HashMapConfiguration::new();
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configuration.insert_variable("a", 6);
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configuration.insert_variable("b", 2);
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configuration.insert_variable("c", 3);
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assert_eq!(precompiled.eval(&configuration), Ok(Value::from(true)));
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configuration.insert_variable("c", 8);
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assert_eq!(precompiled.eval(&configuration), Ok(Value::from(false)));
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```
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## Features
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### Operators
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Supported binary operators:
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| Operator | Precedence | Description | | Operator | Precedence | Description |
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|----------|------------|-------------|---|----------|------------|-------------|
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| + | 95 | Sum | | < | 80 | Lower than |
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| - | 95 | Difference | | \> | 80 | Greater than |
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| * | 100 | Product | | <= | 80 | Lower than or equal |
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| / | 100 | Division | | \>= | 80 | Greater than or equal |
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| % | 100 | Modulo | | == | 80 | Equal |
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| && | 75 | Logical and | | != | 80 | Not equal |
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| || | 70 | Logical or | | | |
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Supported unary operators:
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| Operator | Precedence | Description |
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|----------|------------|-------------|
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| - | 110 | Negation |
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| ! | 110 | Logical not |
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Operators with higher precedence have a higher priority when determining the order of evaluation.
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The precedence of variables and values is 200, and the precedence of function literals is 190.
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### Values
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Operators take values as arguments and produce values as results.
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Values can be boolean, integer or floating point numbers.
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Strings are supported as well, but there are no operations defined for them yet.
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Values are denoted as displayed in the following table.
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| Value type | Example |
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|------------|---------|
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| `Value::Boolean` | `true`, `false` |
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| `Value::Int` | `3`, `-9`, `0`, `135412` |
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| `Value::Float` | `3.`, `.35`, `1.00`, `0.5`, `123.554` |
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Integers are internally represented as `i64`, and floating point numbers are represented as `f64`.
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Operators that take numbers as arguments can either take integers or floating point numbers.
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If one of the arguments is a floating point number, all others are converted to floating point numbers as well, and the resulting value is a floating point number as well.
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Otherwise, the result is an integer.
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Values have a precedence of 200.
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### Variables
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This crate allows to compile parameterizable formulas by using variables.
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A variable is a literal in the formula, that does not contain whitespace or can be parsed as value.
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The user needs to provide bindings to the variables for evaluation.
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This is done with the `Configuration` trait.
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Two structs implementing this trait are predefined.
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There is `EmptyConfiguration`, that returns `None` for each request, and `HashMapConfiguration`, that stores mappings from literals to variables in a hash map.
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Variables do not have fixed types in the expression itself, but aer typed by the configuration.
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The `Configuration` trait contains a function that takes a string literal and returns a `Value` enum.
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The variant of this enum decides the type on evaluation.
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Variables have a precedence of 200.
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### Functions
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This crate also allows to define arbitrary functions to be used in parsed expressions.
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A function is defined as a `Function` instance.
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It contains two properties, the `argument_amount` and the `function`.
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The `function` is a boxed `Fn(&[Value]) -> Result<Value, Error>`.
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The `argument_amount` determines the length of the slice that is passed to `function`.
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It is verified on execution by the crate and does not need to be verified by the `function`.
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Be aware that functions need to verify the types of values that are passed to them.
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The `error` module contains some shortcuts for verification, and error types for passing a wrong value type.
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Also, most numeric functions need to differentiate between being called with integers or floating point numbers, and act accordingly.
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Functions are identified by literals, like variables as well.
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A literal identifies a function, if it is followed by an opening brace `(`, another literal, or a value.
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Same as variables, function bindings are provided by the user via a `Configuration`.
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Functions have a precedence of 190.
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### Examplary variables and functions in expressions:
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| Expression | Valid? | Explanation |
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|------------|--------|-------------|
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| `a` | yes | |
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| `abc` | yes | |
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| `a<b` | no | Expression is interpreted as variable `a`, operator `<` and variable `b` |
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| `a b` | no | Expression is interpreted as function `a` applied to argument `b` |
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| `123` | no | Expression is interpreted as `Value::Int` |
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| `true` | no | Expression is interpreted as `Value::Bool` |
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| `.34` | no | Expression is interpreted as `Value::Float` |
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## License
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This crate is primarily distributed under the terms of the MIT license.
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See [LICENSE](LICENSE) for details.
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<!-- cargo-sync-readme end -->
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