newsletter

newsletter/.exercism/config.json

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+{
+  "authors": [
+    "lpil"
+  ],
+  "files": {
+    "solution": [
+      "src/newsletter.gleam"
+    ],
+    "test": [
+      "test/newsletter_test.gleam"
+    ],
+    "exemplar": [
+      ".meta/example.gleam"
+    ],
+    "invalidator": [
+      "gleam.toml",
+      "manifest.toml"
+    ]
+  },
+  "forked_from": [
+    "elixir/newsletter"
+  ],
+  "blurb": "Learn about IO by sending out a newsletter."
+}

newsletter/.exercism/metadata.json

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+{"track":"gleam","exercise":"newsletter","id":"ec3e4622cebd4906aff5b7b7f8a3e90b","url":"https://exercism.org/tracks/gleam/exercises/newsletter","handle":"fw353qwgs","is_requester":true,"auto_approve":false}

newsletter/.gitignore

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+*.beam
+*.ez
+build
+erl_crash.dump
+log.txt
+emails.txt

newsletter/HELP.md

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+# Help
+
+## Running the tests
+
+To run the tests, run the command `gleam test` from within the exercise directory.
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit src/newsletter.gleam` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Gleam track's documentation](https://exercism.org/docs/tracks/gleam)
+- The [Gleam track's programming category on the forum](https://forum.exercism.org/c/programming/gleam)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+To get help if you're having trouble, you can use one of the following resources:
+
+- [gleam.run](https://gleam.run/documentation/) is the gleam official documentation.
+- [Discord](https://discord.gg/Fm8Pwmy) is the discord channel.
+- [StackOverflow](https://stackoverflow.com/questions/tagged/gleam) can be used to search for your problem and see if it has been answered already. You can also ask and answer questions.

newsletter/HINTS.md

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+# Hints
+
+## 1. Read email addresses from a file
+
+- The [`simplifile.read` function][file-read] can be used to read the contents of a file.
+
+## 2. Create a log file for writing
+
+- The [`simplifile.create_file` function][file-create] can be used to create an empty file.
+
+## 3. Log a sent email
+
+- The [`simplifile.append` function][file-append] can be used to append text to a file.
+
+## 5. Send the newsletter
+
+- All the necessary operations on files were already implemented in the previous steps.
+- The [`result.try` function][result-try] and [`list.try_each` function][list-try-each] can be used to work with the `Result` type.
+
+[file-read]: https://hexdocs.pm/simplifile/simplifile.html#read
+[file-create]: https://hexdocs.pm/simplifile/simplifile.html#create_file
+[file-append]: https://hexdocs.pm/simplifile/simplifile.html#append
+[result-try]: https://hexdocs.pm/gleam_stdlib/gleam/result.html#try
+[list-try-each]: https://hexdocs.pm/gleam_stdlib/gleam/list.html#try_each

newsletter/README.md

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+# Newsletter
+
+Welcome to Newsletter on Exercism's Gleam Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+If you get stuck on the exercise, check out `HINTS.md`, but try and solve it without using those first :)
+
+## Introduction
+
+## Nil
+
+`Nil` in Gleam is a type with a single value, also called `Nil`. It is similar to `void` in other languages in that it is used when a function does not have any more suitable value to return.
+
+```gleam
+io.println("Hello, Joe!")
+// -> Nil
+```
+
+Values in Gleam are not "nil-able" or "nullable" like in some other languages. A value can only be `Nil` if it's type is `Nil`, and a value of any other type can never be `Nil`.
+
+## IO
+
+Like most programming languages Gleam has "side effects", so functions can read and change the state of the world, as well as returning a value.
+
+The `gleam/io` module in the Gleam standard library provides functions for printing strings to the console.
+
+```gleam
+io.println("Hello, Joe!")
+// Hello, Joe!
+// -> Nil
+```
+
+Other packages may provide other IO functions, such as `simplifile`, a package which provides functions for reading and writing files.
+
+```gleam
+simplifile.read("favourite-colour.txt")
+// -> Ok("Pink\n")
+```
+
+## Instructions
+
+Boris is a big model train enthusiast and has decided to share their passion with the world by starting a newsletter. They'll start by sending the first issue of the newsletter to friends and acquaintances that share the hobby, their email addresses are stored in a text file.
+
+Hint: Use the [simplifile](https://hexdocs.pm/simplifile/simplifile.html) module for file operations.
+
+## 1. Read email addresses from a file
+
+Implement the `read_emails` function. It takes a path string to a text file that contains email addresses separated by newlines, and returns a list of the email addresses from the file.
+
+```gleam
+read_emails("/home/my_user/documents/model_train_friends_emails.txt")
+// -> Ok(["rick@example.com", "choochoo42@example.com", "anna@example.com"])
+```
+
+## 2. Create a log file for writing
+
+Sending an email is a task that might fail for many unpredictable reasons, like a typo in the email address or temporary network issues. To ensure that you can retry sending the emails to all your friends without sending duplicates, you need to log the email addresses that already received the email. For this, you'll need a log file.
+
+Implement the `create_log_file` function. It takes a file path and creates a new empty file at that location.
+
+```gleam
+create_log_file("/home/my_user/documents/newsletter_issue1_log.txt")
+// -> Ok(Nil)
+```
+
+## 3. Log a sent email
+
+Implement the `log_sent_email` function. It takes a path to a log file and a string with the email address. It writes the email address to the file, followed by a newline.
+
+```gleam
+log_sent_email(
+  "/home/my_user/documents/newsletter_issue1_log.txt",
+  "joe@example.com",
+)
+// -> Ok(Nil)
+```
+
+## 4. Send the newsletter
+
+Now that you have all of the building blocks of the email sending procedure, you need to combine them together in a single function.
+
+Implement the `send_newsletter` function. It takes a path of the file with email addresses, a path of a log file, and an anonymous function that sends an email to a given email address.
+
+It should read all the email addresses from the given file and attempt to send an email to every one of them. If the anonymous function that sends the email returns an `Ok` value, write the email address to the log file. Make sure to do it as soon as the email is sent.
+
+```gleam
+send_newsletter(
+  "model_train_friends_emails.txt",
+  "newsletter_issue1_log.txt",
+  send_email,
+)
+// -> Ok(Nil)
+```
+
+## Source
+
+### Created by
+
+- @lpil

newsletter/gleam.toml

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+name = "newsletter"
+version = "0.1.0"
+
+[dependencies]
+gleam_otp = "~> 0.7 or ~> 1.0"
+gleam_stdlib = ">= 0.54.0 or ~> 1.0"
+simplifile = "~> 1.0"
+gleam_erlang = ">= 0.25.0 and < 1.0.0"
+gleam_yielder = ">= 1.1.0 and < 2.0.0"
+gleam_regexp = ">= 1.1.0 and < 2.0.0"
+gleam_deque = ">= 1.0.0 and < 2.0.0"
+
+[dev-dependencies]
+exercism_test_runner = "~> 1.9"

newsletter/manifest.toml

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+# This file was generated by Gleam
+# You typically do not need to edit this file
+
+packages = [
+  { name = "argv", version = "1.0.2", build_tools = ["gleam"], requirements = [], otp_app = "argv", source = "hex", outer_checksum = "BA1FF0929525DEBA1CE67256E5ADF77A7CDDFE729E3E3F57A5BDCAA031DED09D" },
+  { name = "exercism_test_runner", version = "1.9.0", build_tools = ["gleam"], requirements = ["argv", "gap", "glance", "gleam_community_ansi", "gleam_erlang", "gleam_json", "gleam_stdlib", "simplifile"], otp_app = "exercism_test_runner", source = "hex", outer_checksum = "0B17BB25F2FF1E60266467C24FE0CA04005410306AA05E9A4B41B1852D72865C" },
+  { name = "filepath", version = "1.1.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "filepath", source = "hex", outer_checksum = "67A6D15FB39EEB69DD31F8C145BB5A421790581BD6AA14B33D64D5A55DBD6587" },
+  { name = "gap", version = "1.1.3", build_tools = ["gleam"], requirements = ["gleam_community_ansi", "gleam_stdlib"], otp_app = "gap", source = "hex", outer_checksum = "6EF5E3B523FDFBC317E9EA28D5163EE04744A97C007106F90207569789612291" },
+  { name = "glance", version = "1.1.0", build_tools = ["gleam"], requirements = ["gleam_stdlib", "glexer"], otp_app = "glance", source = "hex", outer_checksum = "E155BA1A787FD11827048355021C0390D2FE9A518485526F631A9D472858CC6D" },
+  { name = "gleam_community_ansi", version = "1.4.3", build_tools = ["gleam"], requirements = ["gleam_community_colour", "gleam_regexp", "gleam_stdlib"], otp_app = "gleam_community_ansi", source = "hex", outer_checksum = "8A62AE9CC6EA65BEA630D95016D6C07E4F9973565FA3D0DE68DC4200D8E0DD27" },
+  { name = "gleam_community_colour", version = "2.0.0", build_tools = ["gleam"], requirements = ["gleam_json", "gleam_stdlib"], otp_app = "gleam_community_colour", source = "hex", outer_checksum = "FDD6AC62C6EC8506C005949A4FCEF032038191D5EAAEC3C9A203CD53AE956ACA" },
+  { name = "gleam_deque", version = "1.0.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_deque", source = "hex", outer_checksum = "64D77068931338CF0D0CB5D37522C3E3CCA7CB7D6C5BACB41648B519CC0133C7" },
+  { name = "gleam_erlang", version = "0.34.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_erlang", source = "hex", outer_checksum = "0C38F2A128BAA0CEF17C3000BD2097EB80634E239CE31A86400C4416A5D0FDCC" },
+  { name = "gleam_json", version = "2.3.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_json", source = "hex", outer_checksum = "C55C5C2B318533A8072D221C5E06E5A75711C129E420DD1CE463342106012E5D" },
+  { name = "gleam_otp", version = "0.16.1", build_tools = ["gleam"], requirements = ["gleam_erlang", "gleam_stdlib"], otp_app = "gleam_otp", source = "hex", outer_checksum = "50DA1539FC8E8FA09924EB36A67A2BBB0AD6B27BCDED5A7EF627057CF69D035E" },
+  { name = "gleam_regexp", version = "1.1.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_regexp", source = "hex", outer_checksum = "7F5E0C0BBEB3C58E57C9CB05FA9002F970C85AD4A63BA1E55CBCB35C15809179" },
+  { name = "gleam_stdlib", version = "0.55.0", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "32D8F4AE03771516950047813A9E359249BD9FBA5C33463FDB7B953D6F8E896B" },
+  { name = "gleam_yielder", version = "1.1.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_yielder", source = "hex", outer_checksum = "8E4E4ECFA7982859F430C57F549200C7749823C106759F4A19A78AEA6687717A" },
+  { name = "glexer", version = "2.2.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "glexer", source = "hex", outer_checksum = "5C235CBDF4DA5203AD5EAB1D6D8B456ED8162C5424FE2309CFFB7EF438B7C269" },
+  { name = "simplifile", version = "1.7.0", build_tools = ["gleam"], requirements = ["filepath", "gleam_stdlib"], otp_app = "simplifile", source = "hex", outer_checksum = "1D5DFA3A2F9319EC85825F6ED88B8E449F381B0D55A62F5E61424E748E7DDEB0" },
+]
+
+[requirements]
+exercism_test_runner = { version = "~> 1.9" }
+gleam_deque = { version = ">= 1.0.0 and < 2.0.0" }
+gleam_erlang = { version = ">= 0.25.0 and < 1.0.0" }
+gleam_otp = { version = "~> 0.7 or ~> 1.0" }
+gleam_regexp = { version = ">= 1.1.0 and < 2.0.0" }
+gleam_stdlib = { version = ">= 0.54.0 or ~> 1.0" }
+gleam_yielder = { version = ">= 1.1.0 and < 2.0.0" }
+simplifile = { version = "~> 1.0" }

newsletter/src/newsletter.gleam

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+import gleam/string
+import simplifile
+
+pub fn read_emails(path: String) -> Result(List(String), Nil) {
+  case simplifile.read(path) {
+    Error(_) -> Error(Nil)
+    Ok(content) ->
+      string.trim(content)
+      |> string.split("\n")
+      |> Ok
+  }
+}
+
+pub fn create_log_file(path: String) -> Result(Nil, Nil) {
+  case simplifile.create_file(path) {
+    Error(_) -> Error(Nil)
+    Ok(_) -> Ok(Nil)
+  }
+}
+
+pub fn log_sent_email(path: String, email: String) -> Result(Nil, Nil) {
+  case simplifile.append(path, email <> "\n") {
+    Error(_) -> Error(Nil)
+    Ok(_) -> Ok(Nil)
+  }
+}
+
+pub fn send_newsletter(
+  emails_path: String,
+  log_path: String,
+  send_email: fn(String) -> Result(Nil, Nil),
+) -> Result(Nil, Nil) {
+  case create_log_file(log_path), read_emails(emails_path) {
+    Ok(_), Ok(emails) -> send_emails_and_log(emails, send_email, log_path)
+    _, _ -> Error(Nil)
+  }
+}
+
+fn send_emails_and_log(
+  emails: List(String),
+  send_fn: fn(String) -> Result(Nil, Nil),
+  log_path: String,
+) -> Result(Nil, Nil) {
+  let _ = case emails {
+    [] -> Ok(Nil)
+    [email, ..rest] -> {
+      let _ = case send_fn(email) {
+        Error(_) -> Error(Nil)
+        Ok(_) -> log_sent_email(log_path, email)
+      }
+      send_emails_and_log(rest, send_fn, log_path)
+    }
+  }
+}
+// It should read all the email addresses from the given file and attempt to send an email to every one of them. If the anonymous function that sends the email returns an `Ok` value, write the email address to the log file. Make sure to do it as soon as the email is sent.

newsletter/test/newsletter_test.gleam

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+import exercism/should
+import exercism/test_runner
+import newsletter
+import simplifile
+
+pub fn main() {
+  test_runner.main()
+}
+
+pub fn read_emails_test() {
+  let emails =
+    "lucy@example.com
+thomas@example.com
+sid@example.com
+"
+  let assert Ok(_) = simplifile.write("emails.txt", emails)
+  let assert Ok(emails) = newsletter.read_emails("emails.txt")
+  emails
+  |> should.equal(["lucy@example.com", "thomas@example.com", "sid@example.com"])
+}
+
+pub fn create_log_file_test() {
+  let _ = simplifile.delete("log.txt")
+  let assert Ok(Nil) = newsletter.create_log_file("log.txt")
+  let assert Ok(log) = simplifile.read("log.txt")
+  log
+  |> should.equal("")
+}
+
+pub fn log_sent_email_test() {
+  let _ = simplifile.delete("log.txt")
+  let assert Ok(Nil) = newsletter.create_log_file("log.txt")
+  let assert Ok(Nil) =
+    newsletter.log_sent_email("log.txt", "janice@example.com")
+
+  let assert Ok(log) = simplifile.read("log.txt")
+  log
+  |> should.equal("janice@example.com\n")
+
+  let assert Ok(Nil) = newsletter.log_sent_email("log.txt", "joe@example.com")
+  let assert Ok(log) = simplifile.read("log.txt")
+  log
+  |> should.equal("janice@example.com\njoe@example.com\n")
+}
+
+pub fn send_newsletter_test() {
+  let _ = simplifile.delete("log.txt")
+  let emails =
+    "bushra@example.com
+abdi@example.com
+bell@example.com
+"
+  let assert Ok(Nil) = simplifile.write("emails.txt", emails)
+
+  let send_email = fn(email) {
+    case email {
+      "bushra@example.com" -> {
+        let assert Ok(log) = simplifile.read("log.txt")
+        log
+        |> should.equal("")
+        Ok(Nil)
+      }
+      "abdi@example.com" -> {
+        let assert Ok(log) = simplifile.read("log.txt")
+        log
+        |> should.equal("bushra@example.com\n")
+        Error(Nil)
+      }
+      "bell@example.com" -> {
+        let assert Ok(log) = simplifile.read("log.txt")
+        log
+        |> should.equal("bushra@example.com\n")
+        Ok(Nil)
+      }
+      _ -> panic as "Unexpected email given to send_email function"
+    }
+  }
+
+  let assert Ok(Nil) =
+    newsletter.send_newsletter("emails.txt", "log.txt", send_email)
+
+  let assert Ok(log) = simplifile.read("log.txt")
+  log
+  |> should.equal("bushra@example.com\nbell@example.com\n")
+}