Haskell：获取表达式的静态类型

本文介绍了Haskell：获取表达式的静态类型的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 29岁程序员，3月因学历无情被辞！ 理想情况下，它的签名类似于 getStaticType :: a - >字符串 a = getStaticType（1 + 2） - a =（Num t）=> t b = getStaticType zipWith - - b =（a - > b - > c） - > [a] - > [b] - > [c] 您可以这样做： import Data.Typeable getStaticType ::可键入的a => a - >字符串 getStaticType = show。 typeOf 请注意，该类型必须是 Typeable 。您可以使用 DeriveDataTypeable Haskell语言扩展和 ...自动派生 Typeable ... deriving（Typeable ，...）。 另请注意，多态类型不能用这种方式标识;您必须始终使用特定的类型调用函数，因此您永远无法获得您在GHCi中使用编译好的Haskell代码获得的多态类型信息。 使用TemplateHaskell，你可以这样做;首先，创建这个模块： 模块TypeOf其中 导入Control.Monad import Language.Haskell.TH import Language.Haskell.TH.Syntax getStaticType :: Name - > Q Exp getStaticType = lift< =< fmap pprint。然后，在不同模块中（非常重要），您可以请执行以下操作： { - ＃LANGUAGE TemplateHaskell＃ - } import TypeOf main = putStrLn $（getStaticType'zipWith） 该程序输出： GHC.List.zipWith :: forall a_0 b_1 c_2。 （a_0→b_1→c_2）→> [a_0] - > [b_1] - > [c_2] 您可以使用比 pprint 函数;请查看 Language.Haskell.TH.Ppr 模块。 I'm looking for a function that does what the GHCi :type command does.Ideally, it would have a signature something likegetStaticType :: a -> Stringa = getStaticType (1+2)-- a = "(Num t) => t"b = getStaticType zipWith-- b = "(a -> b -> c) -> [a] -> [b] -> [c]"(Note: this has nothing to do with Data.Dynamic. I just want the static type inferred from the compiler. In fact the function wouldn't need a runtime implementation at all, as all calls to it could be inlined as constants at compile time. I'm assuming it exists somewhere, since GHCi can do it) 解决方案 You can do it like this:import Data.TypeablegetStaticType :: Typeable a => a -> StringgetStaticType = show . typeOfNote that the type must be an instance of Typeable. You can derive Typeable automatically using the DeriveDataTypeable Haskell language extension and ... deriving (Typeable, ...).Also note that polymorphic types cannot be identified in this way; you must always call a function with a specific type, so you can never get that polymorphic type information that you get in GHCi with compiled Haskell code.The way GHCi does it is that it uses the GHC API to analyse an intermediary Haskell abstract syntax tree (AST) that contains type information. GHCi does not have the same restricted environment that your typical compiled Haskell program does; it can do lots of stuff to find out more information about its environment.With TemplateHaskell, you can do it like this; first, create this module:module TypeOf whereimport Control.Monadimport Language.Haskell.THimport Language.Haskell.TH.SyntaxgetStaticType :: Name -> Q ExpgetStaticType = lift <=< fmap pprint . reifyThen, in a different module (very important), you can do the following:{-# LANGUAGE TemplateHaskell #-}import TypeOfmain = putStrLn $(getStaticType 'zipWith)This program outputs:GHC.List.zipWith :: forall a_0 b_1 c_2 . (a_0 -> b_1 -> c_2) -> [a_0] -> [b_1] -> [c_2]You can use a better pretty-printer than the pprint function; take a look at the Language.Haskell.TH.Ppr module. 这篇关于Haskell：获取表达式的静态类型的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！