com.github.sommeri.less4j.LessFunction Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of less4j Show documentation

Less language is an extension of css and less4j compiles it into regular css. It adds several dynamic features into css: variables, expressions, nested rules. Less4j is a port. The original compiler was written in JavaScript and is called less.js. The less language is mostly defined in less.js documentation/issues and by what less.js actually do. Links to less.js: * home page: http://lesscss.org/ * source code & issues: https://github.com/cloudhead/less.js

There is a newer version: 1.17.2

Show newest version

package com.github.sommeri.less4j;

import java.util.List;

import com.github.sommeri.less4j.core.ast.ComposedExpression;
import com.github.sommeri.less4j.core.ast.Expression;
import com.github.sommeri.less4j.core.ast.FunctionExpression;

/**
 * Implement this interface to create custom less function. 
 *
 */
public interface LessFunction {

  /**
   * Returns true if this function can evaluate the less function.    
   * 
   * @param input - function to be evaluated
   * @param parameters - function parameters 
   * 
   * @return true only if the implementation can evaluate the input function.
   */
  public boolean canEvaluate(FunctionExpression input, List parameters);

  /**
   * Evaluates less function in parameter. Will be called only if {@link #canEvaluate(FunctionExpression, List)} returns true.
   * 
   * The evaluatedParameter contains function arguments as parsed into a single abstract 
   * syntax tree node. A function called with multiple arguments would be sent an instance of 
   * {@link ComposedExpression} with  arguments bundled in as childs. 
   * 
   * The evaluatedParameter contains list of function arguments. It is convenience argument 
   * and contains evaluatedParameter expression split by commas.
   * 
   * @param input - input function
   * @param parameters - function arguments split (evaluated)
   * @param evaluatedParameter - all function arguments as a single expression (evaluated)  
   * @param problems - errors and warnings collector
   * 
   * @return result of function evaluation. Must NOT return null and should return 
   *     correct abstract syntax tree node. Eg. 
   *     * solved parent child relationships (both ways), 
   *     * each node instance can appear in the three only once,
   *     * correctly filled underlying structure properties.
   */
  public Expression evaluate(FunctionExpression input, List parameters, Expression evaluatedParameter, LessProblems problems);

}