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PORecursive expression whose only base case is an exception [Context: Reading from files in OCaml]
 

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  1. PORecursive expression whose only base case is an exception [Context: Reading from files in OCaml]
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    <p><em><strong>Edit: Disregard this question! See comments below.</em></strong></p> <p>I want an OCaml expression which is passed a file (as an "in_channel"), then reads the file line by line, doing some processing, to the end, then returns the result of the processing.</p> <p>I wrote this test:</p> <pre><code>let rec sampler_string file string_so_far = try let line = input_line file in let first_two_letters = String.sub line 0 2 in sampler_string file (string_so_far ^ first_two_letters) with End_of_file -&gt; string_so_far;; let a = sampler_string (open_in Sys.argv.(1)) "";; </code></pre> <p>(Here the "doing some processing" is adding the first two characters of each line to a running tally, and the idea is that at the end a string containing the first two characters of every line should be returned.)</p> <p>This doesn't work: <strong>OCaml thinks that "sampler_string" produces something of type unit, rather than of type string</strong>. (Difficulties then occur later when I try to use the result as a string.) I think this problem is because <strong>the only base case happens in an exception</strong> (the End_of_file).</p> <p>So, a specific question and a general question:</p> <ol> <li>Is there a way to fix this code, by explicitly telling OCaml to expect that the result of sampler_string should be a string?</li> <li>Is there some standard, better syntax for a routine which reads a file line by line to the end, and returns the result of line-by-line processing?</li> </ol>
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    1. COThis is what OCaml 3.12 says of your function definition here: `val sampler_string : in_channel -> string -> string = <fun>`... looks ok to me
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      1. USDamien Pollet
    2. COHi @Damien, you're totally right. I misunderstood the source of an error. Thanks for the help.
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