Haskell - 実践Haskell - Aesonfを使ったJSONデータの処理 - NOAAデータを読む取る - ToJSON
入門Haskellプログラミング (Will Kurt(著)、株式会社クイープ(監修、翻訳)、翔泳社)の UNIT 7(実践Haskell)、LESSON 40(Aesonfを使ったJSONデータの処理)、40.6(練習問題)、Q40-1の解答を求めてみる。
軽量マークアップ言語
json-lesson/package.yaml
name: json-lesson
version: 0.1.0.0
github: "githubuser/json-lesson"
license: BSD-3-Clause
author: "Author name here"
maintainer: "example@example.com"
copyright: "2025 Author name here"
extra-source-files:
- README.md
- CHANGELOG.md
# Metadata used when publishing your package
# synopsis: Short description of your package
# category: Web
# To avoid duplicated efforts in documentation and dealing with the
# complications of embedding Haddock markup inside cabal files, it is
# common to point users to the README.md file.
description: Please see the README on GitHub at <https://github.com/githubuser/json-lesson#readme>
dependencies:
- base >= 4.7 && < 5
- aeson
- bytestring
- text
default-extensions:
- OverloadedStrings
- DeriveGeneric
ghc-options:
- -Wall
- -Wcompat
- -Widentities
- -Wincomplete-record-updates
- -Wincomplete-uni-patterns
- -Wmissing-export-lists
- -Wmissing-home-modules
- -Wpartial-fields
- -Wredundant-constraints
library:
source-dirs: src
executables:
json-lesson-exe:
main: Main.hs
source-dirs: app
ghc-options:
- -threaded
- -rtsopts
- -with-rtsopts=-N
dependencies:
- json-lesson
tests:
json-lesson-test:
main: Spec.hs
source-dirs: test
ghc-options:
- -threaded
- -rtsopts
- -with-rtsopts=-N
dependencies:
- json-lesson
コード
json-lesson/app/Main.hs
module Main (main) where
-- import Lib
import qualified Data.Text as T
-- import qualified Data.ByteString.Lazy as B
import GHC.Generics
import Data.Aeson
data Resultset = Resultset {
offset :: Int,
count :: Int,
limit :: Int
} deriving (Show, Generic)
instance ToJSON Resultset
data Metadata = Metadata {
resultset :: Resultset
} deriving (Show, Generic)
instance ToJSON Metadata
data NOAAResult = NOAAResult {
uid :: T.Text,
mindate :: T.Text,
maxdate :: T.Text,
name :: T.Text,
datacoverage :: Double,
resultId :: T.Text
} deriving Show
instance ToJSON NOAAResult where
toJSON (NOAAResult uid mindate maxdate name datacoverage resultId) =
object [ "uid" .= uid,
"mindate" .= mindate,
"maxdate" .= maxdate,
"name" .= name,
"datacoverage" .= datacoverage,
"id" .= resultId]
data NOAAResponse = NOAAResponse {
metadata :: Metadata,
results :: [NOAAResult]
} deriving (Show, Generic)
instance ToJSON NOAAResponse
response :: NOAAResponse
response = NOAAResponse {
metadata = Metadata {
resultset = Resultset {
offset = 2,
count = 10,
limit = 100
}
},
results = [
NOAAResult {
uid = "a",
mindate = "11",
maxdate = "22",
name = "Name",
datacoverage = 1.2,
resultId = "result id1"
},
NOAAResult {
uid = "b",
mindate = "11",
maxdate = "22",
name = "Name",
datacoverage = 1.2,
resultId = "result id2"
}
]
}
main :: IO ()
main = do
print response
print $ toJSON response
入出力結果(Terminal, Zsh)
% stack run
json-lesson-0.1.0.0: unregistering (local file changes: app/Main.hs)
json-lesson> build (lib + exe) with ghc-9.8.4
Preprocessing library for json-lesson-0.1.0.0..
Building library for json-lesson-0.1.0.0..
Preprocessing executable 'json-lesson-exe' for json-lesson-0.1.0.0..
Building executable 'json-lesson-exe' for json-lesson-0.1.0.0..
[1 of 2] Compiling Main [Source file changed]
/Users/.../json-lesson/app/Main.hs:33:24: warning: [GHC-63397] [-Wname-shadowing]
This binding for ‘uid’ shadows the existing binding
defined at app/Main.hs:24:5
|
33 | toJSON (NOAAResult uid mindate maxdate name datacoverage resultId) =
| ^^^
/Users/.../json-lesson/app/Main.hs:33:28: warning: [GHC-63397] [-Wname-shadowing]
This binding for ‘mindate’ shadows the existing binding
defined at app/Main.hs:25:5
|
33 | toJSON (NOAAResult uid mindate maxdate name datacoverage resultId) =
| ^^^^^^^
/Users/.../json-lesson/app/Main.hs:33:36: warning: [GHC-63397] [-Wname-shadowing]
This binding for ‘maxdate’ shadows the existing binding
defined at app/Main.hs:26:5
|
33 | toJSON (NOAAResult uid mindate maxdate name datacoverage resultId) =
| ^^^^^^^
/Users/.../json-lesson/app/Main.hs:33:44: warning: [GHC-63397] [-Wname-shadowing]
This binding for ‘name’ shadows the existing binding
defined at app/Main.hs:27:5
|
33 | toJSON (NOAAResult uid mindate maxdate name datacoverage resultId) =
| ^^^^
/Users/.../json-lesson/app/Main.hs:33:49: warning: [GHC-63397] [-Wname-shadowing]
This binding for ‘datacoverage’ shadows the existing binding
defined at app/Main.hs:28:5
|
33 | toJSON (NOAAResult uid mindate maxdate name datacoverage resultId) =
| ^^^^^^^^^^^^
/Users/.../json-lesson/app/Main.hs:33:62: warning: [GHC-63397] [-Wname-shadowing]
This binding for ‘resultId’ shadows the existing binding
defined at app/Main.hs:29:5
|
33 | toJSON (NOAAResult uid mindate maxdate name datacoverage resultId) =
| ^^^^^^^^
[3 of 3] Linking .stack-work/dist/aarch64-osx/ghc-9.8.4/build/json-lesson-exe/json-lesson-exe [Objects changed]
ld: warning: -U option is redundant when using -undefined dynamic_lookup
json-lesson> copy/register
Installing library in /Users/.../json-lesson/.stack-work/install/aarch64-osx/27e00dd04a6f7fc061662d4eebb16cc69859af4840b4ab18e626ce23aacafb60/9.8.4/lib/aarch64-osx-ghc-9.8.4/json-lesson-0.1.0.0-5hrW8Xn7EXr6hNkAQFVUwP
Installing executable json-lesson-exe in /Users/.../json-lesson/.stack-work/install/aarch64-osx/27e00dd04a6f7fc061662d4eebb16cc69859af4840b4ab18e626ce23aacafb60/9.8.4/bin
Registering library for json-lesson-0.1.0.0..
NOAAResponse {metadata = Metadata {resultset = Resultset {offset = 2, count = 10, limit = 100}}, results = [NOAAResult {uid = "a", mindate = "11", maxdate = "22", name = "Name", datacoverage = 1.2, resultId = "result id1"},NOAAResult {uid = "b", mindate = "11", maxdate = "22", name = "Name", datacoverage = 1.2, resultId = "result id2"}]}
Object (fromList [("metadata",Object (fromList [("resultset",Object (fromList [("count",Number 10.0),("limit",Number 100.0),("offset",Number 2.0)]))])),("results",Array [Object (fromList [("datacoverage",Number 1.2),("id",String "result id1"),("maxdate",String "22"),("mindate",String "11"),("name",String "Name"),("uid",String "a")]),Object (fromList [("datacoverage",Number 1.2),("id",String "result id2"),("maxdate",String "22"),("mindate",String "11"),("name",String "Name"),("uid",String "b")])])])
%