PragmaticGP_pile1.feature

Feature: Pile interpreter handles tokens as expected
  In order to get consistent behavior when executing Pile scripts
  As a symbolic regression modeler
  I want each of the six basic token types to bring about expected changes in the Pile interpreter stack

  Scenario: numerical constants are pushed onto the interpreter stack
    Given the Pile script "-91.21"
    When I execute it
    Then there should be 1 item on the stack
    And the top stack item should be -91.21

  Scenario: only traditional floating-point numbers are recognized
    Given the Pile script "-91.21e61.7"
    When I execute it
    Then the stack should be empty
    And no errors should occur

  Scenario: addition pushes the sum of 2 stack items
    Given the Pile script "1.2 3.4 +"
    When I execute it
    Then there should be 1 item on the stack
    And the top stack item should be 4.7

  Scenario: subtraction pushes the difference of 2 stack items 
    Given the Pile script "1.2 3.4 -"
    When I execute it
    Then there should be 1 item on the stack
    And the top stack item should be -2.2

  Scenario: multiplication pushes the product of 2 stack items
    Given the Pile script "1.2 3.4 *"
    When I execute it
    Then there should be 1 item on the stack
    And the top stack item should be 4.08

  Scenario: division pushes the quotient of 2 stack items
    Given the Pile script "8.2 -2.0 /"
    When I execute it
    Then there should be 1 item on the stack
    And the top stack item should be 4.1

  Scenario: x pushes the bound value
    Given the Pile script "x"
    When I execute it with x = 2.1
    Then there should be 1 item on the stack
    And the top stack item should be 2.1

  Scenario: instructions with missing arguments fail silently
    Given the Pile script "9.1 *"
    When I execute it
    Then the top stack item should be 9.1
    And there should be 1 item on the stack
    And no errors should occur

  Scenario: instructions with no arguments fail silently
    Given the Pile script "+ / + *"
    When I execute it
    Then the stack should be empty
    And no errors should occur

  Scenario: division by zero ("protected division") results in 0.0
    Given the Pile script "8.2 -0.0 /"
    When I execute it
    Then there should be 1 item on the stack
    And the top stack item should be 0.0
    And no errors should occur

  Scenario: gibberish tokens fail silently
    Given the Pile script "foo bar"
    When I execute it
    Then the stack should be empty
    And no errors should occur

  Scenario: empty scripts do nothing
    Given the Pile script ""
    When I execute it
    Then the stack should be empty
    And no errors should occur

  Scenario: script execution leaves all resulting items on the stack
    Given the Pile script "1.1 2.2 3.3 4.4 x"
    When I execute it with x = 5.5
    Then there should be 5 items on the stack
    And the top stack item should be 5.5
    And the bottom stack item should be 1.1