相关疑难解决方法(0)

我有以下课程:

class SappState s where
    getTable   :: s -> SymbolTable
    getStack   :: s -> Stack Scope
    getScopeId :: s -> ScopeNum
    getAst     :: s -> Program
    putTable   :: SymbolTable -> s -> s
    putStack   :: Stack Scope -> s -> s
    putScopeId :: ScopeNum    -> s -> s
    putAst     :: Program     -> s -> s

我总是show在datas表示这个实例class在它定义的函数.所以我用以下代码概括了它:

instance (SappState s) => Show s where
    show st = showT ++ showS ++ showI ++ …