expressive/src/lib.rs

//!
//! ## Quickstart
//!
//! Add `evalexpr` as dependency to your `Cargo.toml`:
//!
//! ```toml
//! [dependencies]
//! evalexpr = "1"
//! ```
//!
//! Add the `extern crate` definition to your `main.rs` or `lib.rs`:
//!
//! ```rust
//! extern crate evalexpr;
//! ```
//!
//! Then you can use `evalexpr` to evaluate expressions like this:
//!
//! ```rust
//! use evalexpr::*;
//!
//! assert_eq!(eval("1 + 2 + 3"), Ok(Value::from(6)));
//! // `eval` returns a variant of the `Value` enum,
//! // while `eval_[type]` returns the respective type directly.
//! // Both can be used interchangeably.
//! assert_eq!(eval_int("1 + 2 + 3"), Ok(6));
//! assert_eq!(eval("1 - 2 * 3"), Ok(Value::from(-5)));
//! assert_eq!(eval("1.0 + 2 * 3"), Ok(Value::from(7.0)));
//! assert_eq!(eval("true && 4 > 2"), Ok(Value::from(true)));
//! ```
//!
//! And you can use variables and functions in expressions like this:
//!
//! ```rust
//! use evalexpr::*;
//! use evalexpr::error::expect_number;
//!
//! let mut configuration = HashMapConfiguration::new();
//! configuration.insert_variable("five", 5);
//! configuration.insert_variable("twelve", 12);
//! configuration.insert_function("f", Function::new(Some(1) /* argument amount */, Box::new(|arguments| {
//!     if let Value::Int(int) = arguments[0] {
//!         Ok(Value::Int(int / 2))
//!     } else if let Value::Float(float) = arguments[0] {
//!         Ok(Value::Float(float / 2.0))
//!     } else {
//!         Err(Error::expected_number(arguments[0].clone()))
//!     }
//! })));
//! configuration.insert_function("avg", Function::new(Some(2) /* argument amount */, Box::new(|arguments| {
//!     expect_number(&arguments[0])?;
//!     expect_number(&arguments[1])?;
//!
//!     if let (Value::Int(a), Value::Int(b)) = (&arguments[0], &arguments[1]) {
//!         Ok(Value::Int((a + b) / 2))
//!     } else {
//!         Ok(Value::Float((arguments[0].as_float()? + arguments[1].as_float()?) / 2.0))
//!     }
//! })));
//!
//! assert_eq!(eval_with_configuration("five + 8 > f(twelve)", &configuration), Ok(Value::from(true)));
//! // `eval_with_configuration` returns a variant of the `Value` enum,
//! // while `eval_[type]_with_configuration` returns the respective type directly.
//! // Both can be used interchangeably.
//! assert_eq!(eval_boolean_with_configuration("five + 8 > f(twelve)", &configuration), Ok(true));
//! assert_eq!(eval_with_configuration("avg(2, 4) == 3", &configuration), Ok(Value::from(true)));
//! ```
//!
//! You can also precompile expressions like this:
//!
//! ```rust
//! use evalexpr::*;
//!
//! let precompiled = build_operator_tree("a * b - c > 5").unwrap();
//!
//! let mut configuration = HashMapConfiguration::new();
//! configuration.insert_variable("a", 6);
//! configuration.insert_variable("b", 2);
//! configuration.insert_variable("c", 3);
//! assert_eq!(precompiled.eval_with_configuration(&configuration), Ok(Value::from(true)));
//!
//! configuration.insert_variable("c", 8);
//! assert_eq!(precompiled.eval_with_configuration(&configuration), Ok(Value::from(false)));
//! // `Node::eval_with_configuration` returns a variant of the `Value` enum,
//! // while `Node::eval_[type]_with_configuration` returns the respective type directly.
//! // Both can be used interchangeably.
//! assert_eq!(precompiled.eval_boolean_with_configuration(&configuration), Ok(false));
//! ```
//!
//! ## Features
//!
//! ### Operators
//!
//! This crate offers a set of binary and unary operators for building expressions.
//! Operators have a precedence to determine their order of evaluation.
//! The precedence should resemble that of most common programming languages, especially Rust.
//! The precedence of variables and values is 200, and the precedence of function literals is 190.
//!
//! Supported binary operators:
//!
//! | Operator | Precedence | Description |   | Operator | Precedence | Description |
//! |----------|------------|-------------|---|----------|------------|-------------|
//! | + | 95 | Sum | | < | 80 | Lower than |
//! | - | 95 | Difference | | \> | 80 | Greater than |
//! | * | 100 | Product | | <= | 80 | Lower than or equal |
//! | / | 100 | Division | | \>= | 80 | Greater than or equal |
//! | % | 100 | Modulo | | == | 80 | Equal |
//! | ^ | 120 | Exponentiation | | != | 80 | Not equal |
//! | && | 75 | Logical and | | , | 40 | Aggregation |
//! | &#124;&#124; | 70 | Logical or | | | | |
//!
//! Supported unary operators:
//!
//! | Operator | Precedence | Description |
//! |----------|------------|-------------|
//! | - | 110 | Negation |
//! | ! | 110 | Logical not |
//!
//! #### The Aggregation Operator
//!
//! The aggregation operator aggregates two values into a tuple.
//! If one of the values is a tuple already, the resulting tuple will be flattened.
//! Example:
//!
//! ```rust
//! use evalexpr::*;
//!
//! assert_eq!(eval("1, 2, 3"), Ok(Value::from(vec![Value::from(1), Value::from(2), Value::from(3)])));
//! ```
//!
//! ### Builtin Functions
//!
//! This crate offers a set of builtin functions.
//!
//! | Identifier | Argument Amount | Description |
//! |------------|-----------------|-------------|
//! | min | >= 1 | Returns the minimum of the arguments |
//! | max | >= 1 | Returns the maximum of the arguments |
//!
//! The `min` and `max` functions can deal with a mixture of integer and floating point arguments.
//! They return the result as the type it was passed into the function.
//!
//! ### Values
//!
//! Operators take values as arguments and produce values as results.
//! Values can be boolean, integer or floating point numbers.
//! Strings are supported as well, but there are no operations defined for them yet.
//! Values are denoted as displayed in the following table.
//!
//! | Value type | Example |
//! |------------|---------|
//! | `Value::Boolean` | `true`, `false` |
//! | `Value::Int` | `3`, `-9`, `0`, `135412` |
//! | `Value::Float` | `3.`, `.35`, `1.00`, `0.5`, `123.554` |
//!
//! Integers are internally represented as `i64`, and floating point numbers are represented as `f64`.
//! Values can be constructed either directly or using the `From` trait.
//! Values can be decomposed using the `Value::as_[type]` methods.
//! The type of a value can be checked using the `Value::is_[type]` methods.
//!
//! **Examples for constructing a value:**
//!
//! | Code | Result |
//! |------|--------|
//! | `Value::from(4)` | `Value::Int(4)` |
//! | `Value::from(4.4)` | `Value::Float(4.4)` |
//! | `Value::from(true)` | `Value::Boolean(true)` |
//! | `Value::from(vec![Value::from(3)])` | `Value::Tuple(vec![Value::Int(3)])` |
//!
//! **Examples for deconstructing a value:**
//!
//! | Code | Result |
//! |------|--------|
//! | `Value::from(4).as_int()` | `Ok(4)` |
//! | `Value::from(4.4).as_float()` | `Ok(4.4)` |
//! | `Value::from(true).as_int()` | `Err(Error::ExpectedInt {actual: Value::Boolean(true)})` |
//!
//! Operators that take numbers as arguments can either take integers or floating point numbers.
//! 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.
//! Otherwise, the result is an integer.
//! An exception to this is the exponentiation operator that always returns a floating point number.
//!
//! Values have a precedence of 200.
//!
//! ### Variables
//!
//! This crate allows to compile parameterizable formulas by using variables.
//! A variable is a literal in the formula, that does not contain whitespace or can be parsed as value.
//! The user needs to provide bindings to the variables for evaluation.
//! This is done with the `Configuration` trait.
//! Two structs implementing this trait are predefined.
//! There is `EmptyConfiguration`, that returns `None` for each request, and `HashMapConfiguration`, that stores mappings from literals to variables in a hash map.
//!
//! Variables do not have fixed types in the expression itself, but aer typed by the configuration.
//! The `Configuration` trait contains a function that takes a string literal and returns a `Value` enum.
//! The variant of this enum decides the type on evaluation.
//!
//! Variables have a precedence of 200.
//!
//! ### User-Defined Functions
//!
//! This crate also allows to define arbitrary functions to be used in parsed expressions.
//! A function is defined as a `Function` instance.
//! It contains two properties, the `argument_amount` and the `function`.
//! The `function` is a boxed `Fn(&[Value]) -> Result<Value, Error>`.
//! The `argument_amount` determines the length of the slice that is passed to `function` if it is `Some(_)`, otherwise the function is defined to take an arbitrary amount of arguments.
//! It is verified on execution by the crate and does not need to be verified by the `function`.
//!
//! Functions with no arguments are not allowed.
//! Use variables instead.
//!
//! Be aware that functions need to verify the types of values that are passed to them.
//! The `error` module contains some shortcuts for verification, and error types for passing a wrong value type.
//! Also, most numeric functions need to differentiate between being called with integers or floating point numbers, and act accordingly.
//!
//! Functions are identified by literals, like variables as well.
//! A literal identifies a function, if it is followed by an opening brace `(`, another literal, or a value.
//!
//! Same as variables, function bindings are provided by the user via a `Configuration`.
//! Functions have a precedence of 190.
//!
//! ### Examplary variables and functions in expressions:
//!
//! | Expression | Valid? | Explanation |
//! |------------|--------|-------------|
//! | `a` | yes | |
//! | `abc` | yes | |
//! | `a<b` | no | Expression is interpreted as variable `a`, operator `<` and variable `b` |
//! | `a b` | no | Expression is interpreted as function `a` applied to argument `b` |
//! | `123` | no | Expression is interpreted as `Value::Int` |
//! | `true` | no | Expression is interpreted as `Value::Bool` |
//! | `.34` | no | Expression is interpreted as `Value::Float` |
//!
//! ## License
//!
//! This crate is primarily distributed under the terms of the MIT license.
//! See [LICENSE](LICENSE) for details.
//!

#![warn(missing_docs)]

extern crate core;

mod configuration;
pub mod error;
mod function;
mod interface;
mod operator;
mod token;
mod tree;
mod value;

// Exports

pub use configuration::{Configuration, EmptyConfiguration, HashMapConfiguration};
pub use error::Error;
pub use function::Function;
pub use interface::*;
pub use tree::Node;
pub use value::{FloatType, IntType, Value};