Module rubble_templates_core::functions

An API for creating custom functions that extend the features of an evaluator.

Evaluator can be extended with functions by using custom Function trait implementations. To make this process easier, there is evaluator::functions module that contains structs that can be used with static functions and lambdas:

• SimpleFunction - Use this when you want to implement a simple function without any side effects.
• FunctionWithContext - Use this when you want to use pre-evaluated parameters, but you still need variables. Side effects can cause errors indicated by SyntaxError.
• FunctionWithAst - Gives full access to SyntaxNodes of parameters and Evaluator. Allows evaluating additional expressions, manipulating the AST or introducing DSL (domain-specific language).

Mind you, Context is a struct that holds variables and states that can be shared between function invocations. You can use it to store some properties.

Examples for each struct are provided in the documentation. Refer to the generated docs for more specific info.

Basic example:

use std::collections::HashMap;
use rubble_templates_core::functions::SimpleFunction;
use rubble_templates_core::evaluator::Function;

fn plus_function(parameters: &[String]) -> String {
    parameters.iter()
         .map(|param|
             param.parse::<i32>().unwrap()
         )
         .sum::<i32>()
         .to_string()
}

let mut functions: HashMap<String, Box<dyn Function>> = HashMap::new();
functions.insert("plus".to_string(), SimpleFunction::new(plus_function)); // will be treated as Box<dyn Function>

// Now functions can be used with any Evaluator that supports custom functions.
// SimpleEvaluationEngine is the default and it supports such extensions.

Structs

FunctionWithAst	A wrapper for a Fn(&dyn Evaluator, &[SyntaxNode], &mut Context) -> Result<String, SyntaxError>, to be used in Evaluator.
FunctionWithContext	A wrapper for a Fn(&dyn Evaluator, &[String], &mut Context) -> Result<String, SyntaxError>, to be used in Evaluator.
SimpleFunction	A wrapper for a Fn(&[String]) -> String, to be used in Evaluator.

Functions

resolve_params

Resolves a slice of SyntaxNodes to a Vec of strings.