Interface Evaluator

All Known Subinterfaces:
StackEvaluator, StandardEvaluator, StandardStackEvaluator, StandardTreeEvaluator, TreeEvaluator
All Known Implementing Classes:
AbstractEvaluator, AbstractStandardEvaluator, DefaultStackEvaluator, DefaultTreeEvaluator

public interface Evaluator
Interface for expression evaluators.
Author:
Curtis Rueden
  • Method Details

    • getParser

      ExpressionParser getParser()
      Gets the parser used when evaluating expressions.
      Returns:
      The expression parser used by this evaluator.
    • isStrict

      boolean isStrict()
      Gets whether the evaluator is operating in strict mode.
      Returns:
      True iff the evaluator is operating in strict mode.
      See Also:
    • setStrict

      void setStrict(boolean strict)
      Sets whether the evaluator is operating in strict mode. Evaluators operate in strict mode by default.

      When evaluating strictly, usage of an unassigned variable token in a place where its value is needed will generate an IllegalArgumentException with an "Unknown variable" message; in non-strict mode, such a variable will instead be resolved to an object of type Unresolved with the same name as the original variable.

      In cases such as assignment, this may be sufficient to complete the evaluation; for example, the expression foo=bar will complete successfully in non-strict mode, with the variable foo containing an object of type Unresolved and token value "bar". But in cases where the unresolved value is needed as an input for additional operations, the evaluation may still ultimately fail if the operation in question is not defined for unresolved values. For example, the DefaultStackEvaluator will fail with an "Unsupported binary operator" exception when given the expression foo+bar, since foo and bar are unresolved variables, and the + operator cannot handle such objects.

      Parameters:
      strict - True iff the evaluator should operate in strict mode.
    • evaluate

      Object evaluate(String expression)
      Evaluates an infix expression.
      Parameters:
      expression - The infix expression to evaluate.
      Returns:
      The result of the evaluation.
    • evaluate

      Object evaluate(LinkedList<Object> queue)
      Evaluates a postfix token queue.
      Parameters:
      queue - The postfix token queue to evaluate.
      Returns:
      The result of the evaluation.
    • evaluate

      Object evaluate(SyntaxTree syntaxTree)
      Evaluates a syntax tree.
      Parameters:
      syntaxTree - The syntax tree to evaluate.
      Returns:
      The result of the evaluation.
    • value

      default Object value(Object token)
      Gets the value of a token. For variables, returns the value of the variable, throwing an exception if the variable is not set. For literals, returns the token itself.
      Parameters:
      token - The token whose value you want.
      Returns:
      The token's value.
    • var

      default Variable var(Object token)
      Casts the given token to a variable.
      Parameters:
      token - The token to cast to a Variable.
      Returns:
      Variable representation of the token.
      Throws:
      IllegalArgumentException - if the given token is not a Variable.
    • get

      Object get(String name)
      Gets the value of a variable.
      Parameters:
      name - The name of the variable whose value you want.
      Returns:
      The variable's value.
      Throws:
      IllegalArgumentException - If the variable's value is not set, and the evaluator is operating in strict mode.
    • set

      void set(String name, Object value)
      Sets the value of a variable.
      Parameters:
      name - The name of the variable whose value you want to set.
      value - The value to assign to the variable.
    • get

      default Object get(Variable v)
      Gets the value of a variable.
      Parameters:
      v - The variable whose value you want.
      Returns:
      The variable's value.
      Throws:
      IllegalArgumentException - If the variable's value is not set, and the evaluator is operating in strict mode.
    • set

      default void set(Variable v, Object value)
      Sets the value of a variable.
      Parameters:
      v - The variable whose value you want to set.
      value - The value to assign to the variable.
    • setAll

      void setAll(Map<? extends String,? extends Object> map)
      Assigns variables en masse.
      Parameters:
      map - A map from variable names to variable values.