OCaml结合extlib实现文件复制报错：dune构建遇语法错误求助

Looks like your code has a couple of syntax and logic issues that are causing the compiler to throw a fit. Let's break down what's wrong and fix it step by step:

The Root Causes of the Syntax Error #

1. Missing in keyword: In OCaml, when you define nested let bindings inside a let () = block (like your text function), you need to use in to terminate each binding before moving to the next one. Your code didn't have an in after Std.input_list chan, so the compiler couldn't parse the subsequent let filename = ... line.
2. Redundant variable binding: The line let filename = filename in is completely unnecessary—you already defined filename at the top level, so you can just use it directly.
3. Incorrect function usage: let text = text in just re-binds the text function to itself, rather than calling it to read the file content. You need to invoke the function with your input filename to get the actual data.

Corrected Code #

(* example.ml file *)
let read_filename = "example_1.ts"
let filename = "example_2.ts"
let () =
  let text input_filename =
    let chan = open_in input_filename in
    Std.input_list chan
  in
  let file_content = text read_filename in
  Std.output_file ~filename ~text:file_content

Key Fixes Explained #

• Added in right after Std.input_list chan to properly close the text function binding, allowing the compiler to process the rest of the code.
• Replaced the useless let text = text in with let file_content = text read_filename in, which actually calls the text function to read the contents of example_1.ts.
• Updated the Std.output_file call to pass ~text:file_content (the actual file data) instead of the function itself.

As a side note: If you want to make this code more robust, you could wrap the file operations in a try...with block to handle cases where the input file doesn't exist or can't be read. But that's an extra improvement—this corrected code will fix your syntax error and get the basic copy functionality working.

内容的提问来源于stack exchange，提问作者Charlie-Greenman