JSON to ELM Class

Tool Introduction

This "JSON to ELM Class" online tool aims to help Elm developers quickly and efficiently convert complex JSON data structures into type alias and record definitions in the Elm language. In Elm application development, processing JSON data returned by external APIs is a common requirement. Manually writing corresponding data models is not only time-consuming but also prone to errors. This tool intelligently parses the JSON string you provide, automatically identifies its keys, value types, and nesting relationships, thereby generating type definition code that conforms to Elm syntax with one click, greatly improving development efficiency and code accuracy.

Importance of Elm Data Models

In Elm, a strongly typed functional programming language, data models are the backbone of an application. Clear and accurate Elm type definitions provide compile-time safety guarantees, effectively preventing runtime errors. By precisely mapping JSON data to Elm's type alias and record, developers can ensure type consistency in data processing, making the code easier to understand, maintain, and refactor, thereby building more robust and reliable web applications.

How to Use

1. Input JSON Data: Paste the valid JSON string you want to convert into the tool's input area. Ensure the JSON format is correct, for example, using double quotes for keys and string values.
2. Execute Conversion: Click the "Convert" or "Generate Elm Code" button. The tool will immediately parse your JSON structure.
3. Get Elm Type Code: After conversion, the generated Elm type alias and record definitions will be displayed in the output area. You can directly copy this code into your Elm project.

Input Parameter Format and Requirements: Must be a string conforming to JSON specifications, supporting nested objects and arrays.

Output Result Format: Standard Elm type alias and record definitions, following Elm style guidelines, easy to integrate directly into Elm modules.

Usage Example

Below is a practical demonstration of converting nested JSON data into Elm type definitions:

Example Input Data

{
  "id": 101,
  "name": "Alice",
  "isActive": true,
  "roles": ["admin", "editor"],
  "profile": {
    "age": 30,
    "email": "alice@example.com",
    "address": null
  },
  "score": 98.5
}

Expected Output Result

After inputting the above JSON into this tool, you will get the following Elm type definitions:

type alias User =
    { id : Int
    , name : String
    , isActive : Bool
    , roles : List String
    , profile : UserProfile
    , score : Float
    }

type alias UserProfile =
    { age : Int
    , email : String
    , address : Maybe String
    }

Operation Demo: Users simply copy the above "Example Input Data" into the tool's input box, click the convert button, and can see the Elm code shown in "Expected Output Result" in the output box.

JSON to Elm Type Mapping

Understanding how JSON data types map to Elm types is key to using this tool:

• JSON String (e.g., "hello") → Elm String
• JSON Number (e.g., 123, 3.14) → Elm Int or Float (the tool usually automatically determines based on whether there is a decimal or provides options)
• JSON Boolean (e.g., true) → Elm Bool
• JSON Array (e.g., [1, 2]) → Elm List a (where a is the type of array elements)
• JSON Object (e.g., {"key": "value"}) → Elm type alias RecordName = { key : Type }
• JSON Null (e.g., null) → Elm Maybe a (where a is the type of the value that can be null)

Frequently Asked Questions

• Q: What JSON data types does this JSON to ELM tool support? A: This tool supports all basic data types defined in the JSON standard, including String, Number, Boolean, Array, Object, and null values.
• Q: Does the generated Elm type code support nested JSON structures? A: Yes, this tool can intelligently parse and generate Elm type alias and record type definitions corresponding to multi-level nested JSON objects, maintaining structural integrity.
• Q: How to handle fields that may be missing or null in JSON? A: When a JSON field value is null, the tool usually maps it to Elm's Maybe Type (e.g., Maybe String) to reflect its optionality. For completely missing fields, you may need to manually adjust the generated Elm code or provide a default null value in the input JSON.
• Q: Can the generated Elm code directly parse JSON in my project? A: The generated type alias definition is part of the Elm data model. To actually parse JSON strings into these Elm types, you also need to combine it with Elm's Json.Decode module to write corresponding decoders. This tool primarily focuses on generating type definitions.

Notes

• Validity of Input JSON: Please ensure that the JSON string you provide is completely valid; any formatting errors (such as missing quotes, commas, etc.) may lead to conversion failure or incorrect results. You can use an online JSON validator tool for verification.
• Data Type Inference: For Number types in JSON, the tool may try to infer whether it is Int or Float. If there is a decimal, it will usually be inferred as Float; otherwise, it will be Int. If a specific type is required, please manually adjust it in the Elm code.
• Handling of null values: The tool will map null values in JSON to Elm's Maybe type (e.g., Maybe String). This means the field may or may not exist.
• Elm Decoders: This tool only generates Elm's type alias definitions. To actually parse these JSON data in an Elm application, you still need to write corresponding decoders in conjunction with the Json.Decode module.
• Naming Conventions: The generated Elm types and field names will attempt to follow Elm's naming conventions (e.g., type names in PascalCase, field names in camelCase). If your JSON key names do not conform to Elm style, you may need to adjust them manually.