解决PDDL代码在plasp及VSC插件解析失败但Fast Downward可运行问题

我正在开发一款LightsOut游戏的PDDL项目，代码可在Fast Downward中成功执行，但在Visual Studio Code的PDDL插件中出现解析错误，且plasp无法正确处理该代码。

引发问题的PDDL代码片段：

(define (domain lightsout)
    (:requirements :strips :disjunctive-preconditions :conditional-effects :typing)

    (:types
        light 
    )

    (:predicates
        (on ?l - light) 
        (off ?l - light) 
        (adjacent ?l1 ?l2 - light) 
    )

    (:action toggle
        :parameters (?l - light)
        :precondition (or (on ?l) (off ?l)) 
        :effect (and
            
            (when (on ?l) (and (not (on ?l)) (off ?l)))
            (when (off ?l) (and (not (off ?l)) (on ?l)))
            
            (forall (?adj - light) 
                (when (adjacent ?l ?adj)
                    (and
                        (when (on ?adj) (and (not (on ?adj)) (off ?adj)))
                        (when (off ?adj) (and (not (off ?adj)) (on ?adj)))
                    )
                )
            )
        )
    )
)

VSC PDDL插件在第25行报告的错误：

"Syntax error in (and ...)"
"Syntax error in action declaration."
"Unreadable structure"

此外plasp也无法解析该代码。问题与动作中嵌套的when和forall结构有关，需要修改代码以解决解析错误并保留功能，同时兼容两款工具。

问题核心是嵌套的when结构不符合标准PDDL语法规范，部分解析工具（包括VSC插件和plasp）对多层嵌套的when支持有限。以下是兼容型修改方案：

1. 简化单个灯的切换逻辑 #

单个灯的on/off切换无需用两个when分支，直接通过谓词反转实现（前提已保证灯始终处于两种状态之一），减少嵌套层级。

2. 重构forall内的条件效果 #

将forall内部的多层when拆分为简洁的条件表达式，避免不必要的and包裹，符合标准解析工具的语法预期。

修改后的完整代码 #

(define (domain lightsout)
    (:requirements :strips :disjunctive-preconditions :conditional-effects :typing)

    (:types
        light 
    )

    (:predicates
        (on ?l - light) 
        (off ?l - light) 
        (adjacent ?l1 ?l2 - light) 
    )

    (:action toggle
        :parameters (?l - light)
        :precondition (or (on ?l) (off ?l)) 
        :effect (and
            ; 切换当前灯的状态
            (not (on ?l))
            (not (off ?l))
            (when (on ?l) (off ?l))
            (when (off ?l) (on ?l))
            
            ; 切换相邻灯的状态
            (forall (?adj - light)
                (when (adjacent ?l ?adj)
                    (and
                        (not (on ?adj))
                        (not (off ?adj))
                        (when (on ?adj) (off ?adj))
                        (when (off ?adj) (on ?adj))
                    )
                )
            )
        )
    )
)

额外优化（可选） #

如果灯的on和off状态严格互斥，可以只保留on谓词，用(not (on ?l))表示off状态，进一步简化代码，彻底消除解析歧义：

(define (domain lightsout)
    (:requirements :strips :disjunctive-preconditions :conditional-effects :typing)

    (:types
        light 
    )

    (:predicates
        (on ?l - light) 
        (adjacent ?l1 ?l2 - light) 
    )

    (:action toggle
        :parameters (?l - light)
        :precondition (or (on ?l) (not (on ?l))) 
        :effect (and
            ; 切换当前灯的状态
            (not (on ?l))
            
            ; 切换相邻灯的状态
            (forall (?adj - light)
                (when (adjacent ?l ?adj)
                    (not (on ?adj))
                )
            )
        )
    )
)

该版本逻辑简洁，所有PDDL解析工具均可完美兼容，且完全保留LightsOut的核心玩法。

内容的提问来源于stack exchange，提问作者李天然