first two easy exercises

.envrc

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+# shellcheck shell=bash
+# For use with direnv.
+# Installing nix-direnv will ensure a smoother experience.
+use flake

dune-project

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+(lang dune 3.2)
+
+(name exercism)
+
+(generate_opam_files false)
+
+(source
+ (uri https://gitea.vp.mk/vladan/exercism))
+
+(authors "Vladan Popovic")
+(maintainers "Vladan Popovic")
+
+(license LICENSE)
+
+(package
+ (name exercism)
+ (synopsis "Exercism OCaml exercises")
+ (description "Exercism OCaml exercises")
+ (depends ocaml dune)
+ (tags
+  (exercism "Exercism OCaml exercises")))
+
+; See the complete stanza docs at https://dune.readthedocs.io/en/stable/dune-files.html#dune-project

flake.lock

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+{
+  "nodes": {
+    "flake-utils": {
+      "locked": {
+        "lastModified": 1667395993,
+        "narHash": "sha256-nuEHfE/LcWyuSWnS8t12N1wc105Qtau+/OdUAjtQ0rA=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "5aed5285a952e0b949eb3ba02c12fa4fcfef535f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nix-filter": {
+      "locked": {
+        "lastModified": 1666547822,
+        "narHash": "sha256-razwnAybPHyoAyhkKCwXdxihIqJi1G6e1XP4FQOJTEs=",
+        "owner": "numtide",
+        "repo": "nix-filter",
+        "rev": "1a3b735e13e90a8d2fd5629f2f8363bd7ffbbec7",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "nix-filter",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1669867399,
+        "narHash": "sha256-Z8RXSFYOsIsTG96ROKtV0eZ8Q7u4irFWm6ELqfw7mT8=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "38e591dd05ffc8bdf79dc752ba78b05e370416fa",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nix-filter": "nix-filter",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  description = "A flake demonstrating how to build OCaml projects with Dune";
+
+  # Flake dependency specification
+  #
+  # To update all flake inputs:
+  #
+  #     $ nix flake update --commit-lockfile
+  #
+  # To update individual flake inputs:
+  #
+  #     $ nix flake lock --update-input <input> ... --commit-lockfile
+  #
+  inputs = {
+    # Convenience functions for writing flakes
+    flake-utils.url = "github:numtide/flake-utils";
+    # Precisely filter files copied to the nix store
+    nix-filter.url = "github:numtide/nix-filter";
+  };
+
+  outputs = { self, nixpkgs, flake-utils, nix-filter }:
+    # Construct an output set that supports a number of default systems
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        # Legacy packages that have not been converted to flakes
+        legacyPackages = nixpkgs.legacyPackages.${system};
+        # OCaml packages available on nixpkgs
+        ocamlPackages = legacyPackages.ocamlPackages;
+        # Library functions from nixpkgs
+        lib = legacyPackages.lib;
+
+        # Filtered sources (prevents unecessary rebuilds)
+        sources = {
+          ocaml = nix-filter.lib {
+            root = ./.;
+            include = [
+              ".ocamlformat"
+              "dune-project"
+              (nix-filter.lib.inDirectory "bin")
+              (nix-filter.lib.inDirectory "lib")
+              (nix-filter.lib.inDirectory "test")
+            ];
+          };
+
+          nix = nix-filter.lib {
+            root = ./.;
+            include = [
+              (nix-filter.lib.matchExt "nix")
+            ];
+          };
+        };
+      in
+      {
+        # Exposed packages that can be built or run with `nix build` or
+        # `nix run` respectively:
+        #
+        #     $ nix build .#<name>
+        #     $ nix run .#<name> -- <args?>
+        #
+        packages = {
+          # The package that will be built or run by default. For example:
+          #
+          #     $ nix build
+          #     $ nix run -- <args?>
+          #
+          default = self.packages.${system}.exercism;
+
+          exercism = ocamlPackages.buildDunePackage {
+            pname = "exercism";
+            version = "0.1.0";
+            duneVersion = "3";
+            src = sources.ocaml;
+
+            strictDeps = true;
+
+            preBuild = ''
+              dune build exercism.opam
+            '';
+          };
+        };
+
+        # Flake checks
+        #
+        #     $ nix flake check
+        #
+        checks = {
+          # Run tests for the `exercism` package
+          exercism =
+            let
+              # Patches calls to dune commands to produce log-friendly output
+              # when using `nix ... --print-build-log`. Ideally there would be
+              # support for one or more of the following:
+              #
+              # In Dune:
+              #
+              # - have workspace-specific dune configuration files
+              #
+              # In NixPkgs:
+              #
+              # - allow dune flags to be set in in `ocamlPackages.buildDunePackage`
+              # - alter `ocamlPackages.buildDunePackage` to use `--display=short`
+              # - alter `ocamlPackages.buildDunePackage` to allow `--config-file=FILE` to be set
+              patchDuneCommand =
+                let
+                  subcmds = [ "build" "test" "runtest" "install" ];
+                in
+                lib.replaceStrings
+                  (lib.lists.map (subcmd: "dune ${subcmd}") subcmds)
+                  (lib.lists.map (subcmd: "dune ${subcmd} --display=short") subcmds);
+            in
+
+            self.packages.${system}.exercism.overrideAttrs
+              (oldAttrs: {
+                name = "check-${oldAttrs.name}";
+                doCheck = true;
+                buildPhase = patchDuneCommand oldAttrs.buildPhase;
+                checkPhase = patchDuneCommand oldAttrs.checkPhase;
+                # skip installation (this will be tested in the `exercism-app` check)
+                installPhase = "touch $out";
+              });
+
+          # Check Dune and OCaml formatting
+          dune-fmt = legacyPackages.runCommand "check-dune-fmt"
+            {
+              nativeBuildInputs = [
+                ocamlPackages.dune_3
+                ocamlPackages.ocaml
+                legacyPackages.ocamlformat
+              ];
+            }
+            ''
+              echo "checking dune and ocaml formatting"
+              dune build \
+                --display=short \
+                --no-print-directory \
+                --root="${sources.ocaml}" \
+                --build-dir="$(pwd)/_build" \
+                @fmt
+              touch $out
+            '';
+
+          # Check documentation generation
+          dune-doc = legacyPackages.runCommand "check-dune-doc"
+            {
+              ODOC_WARN_ERROR = "true";
+              nativeBuildInputs = [
+                ocamlPackages.dune_3
+                ocamlPackages.ocaml
+                ocamlPackages.odoc
+              ];
+            }
+            ''
+              echo "checking ocaml documentation"
+              dune build \
+                --display=short \
+                --no-print-directory \
+                --root="${sources.ocaml}" \
+                --build-dir="$(pwd)/_build" \
+                @doc
+              touch $out
+            '';
+
+          # Check Nix formatting
+          nixpkgs-fmt = legacyPackages.runCommand "check-nixpkgs-fmt"
+            { nativeBuildInputs = [ legacyPackages.nixpkgs-fmt ]; }
+            ''
+              echo "checking nix formatting"
+              nixpkgs-fmt --check ${sources.nix}
+              touch $out
+            '';
+        };
+
+        # Development shells
+        #
+        #    $ nix develop .#<name>
+        #    $ nix develop .#<name> --command dune build @test
+        #
+        # [Direnv](https://direnv.net/) is recommended for automatically loading
+        # development environments in your shell. For example:
+        #
+        #    $ echo "use flake" > .envrc && direnv allow
+        #    $ dune build @test
+        #
+        devShells = {
+          default = legacyPackages.mkShell {
+            # Development tools
+            packages = [
+              # Source file formatting
+              legacyPackages.nixpkgs-fmt
+              legacyPackages.ocamlformat
+              # For `dune build --watch ...`
+              legacyPackages.fswatch
+              # For `dune build @doc`
+              ocamlPackages.odoc
+              # OCaml editor support
+              ocamlPackages.ocaml-lsp
+              # Nicely formatted types on hover
+              ocamlPackages.ocamlformat-rpc-lib
+              # Fancy REPL thing
+              ocamlPackages.utop
+              ocamlPackages.angstrom
+              ocamlPackages.ounit
+              ocamlPackages.ounit2
+              ocamlPackages.ppx_sexp_conv
+            ];
+
+            # Tools from packages
+            inputsFrom = [
+              self.packages.${system}.exercism
+            ];
+          };
+        };
+      });
+}

hello-world/HELP.md

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+# Help
+
+## Running the tests
+
+A `Makefile` is provided with a default target to compile your solution and run the tests. At the command line in your exercise's directory, type:
+
+```bash
+make
+```
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit hello_world.ml` 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 [OCaml track's documentation](https://exercism.org/docs/tracks/ocaml)
+- The [OCaml track's programming category on the forum](https://forum.exercism.org/c/programming/ocaml)
+- [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:
+
+- [Documentation for the Standard Library](http://caml.inria.fr/pub/docs/manual-ocaml/libref/index.html)
+- [/r/ocaml](https://www.reddit.com/r/ocaml) is the OCaml subreddit.
+- [StackOverflow](http://stackoverflow.com/questions/tagged/ocaml) can be used to search for your problem and see if it has been answered already. You can also ask and answer questions.

hello-world/Makefile

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+default: clean test
+
+test: 
+	dune runtest
+
+clean:
+	dune clean
+
+.PHONY: clean

hello-world/README.md

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+# Hello World
+
+Welcome to Hello World on Exercism's OCaml Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+The classical introductory exercise.
+Just say "Hello, World!".
+
+["Hello, World!"][hello-world] is the traditional first program for beginning programming in a new language or environment.
+
+The objectives are simple:
+
+- Modify the provided code so that it produces the string "Hello, World!".
+- Run the test suite and make sure that it succeeds.
+- Submit your solution and check it at the website.
+
+If everything goes well, you will be ready to fetch your first real exercise.
+
+[hello-world]: https://en.wikipedia.org/wiki/%22Hello,_world!%22_program
+
+## Source
+
+### Created by
+
+- @dvberkel
+
+### Contributed to by
+
+- @daveyarwood
+- @iHiD
+- @kytrinyx
+- @marionebl
+- @Peaupote
+- @sbl
+- @sshine
+- @stevejb71
+
+### Based on
+
+This is an exercise to introduce users to using Exercism - https://en.wikipedia.org/wiki/%22Hello,_world!%22_program

hello-world/dune

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+(executable
+ (name test)
+ (libraries base ounit2))
+
+(alias
+  (name    runtest)
+  (deps    (:x test.exe))
+  (action  (run %{x})))
+
+(alias
+  (name    buildtest)
+  (deps    (:x test.exe)))
+
+(env
+  (dev
+    (flags (:standard -warn-error -A))))

hello-world/dune-project

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+(lang dune 1.1)

hello-world/hello_world.ml

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+let hello = "Hello, World!"

hello-world/hello_world.mli

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+(*
+   Returns "Hello, World!"
+*)
+val hello: string

hello-world/test.ml

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+open OUnit2
+open Hello_world
+
+let ae exp got _test_ctxt = assert_equal ~printer:(fun x -> x) exp got
+
+let tests = [
+  "Say Hi!" >:: ae "Hello, World!" hello;
+]
+
+let () =
+  run_test_tt_main ("Hello World tests" >::: tests)

leap/HELP.md

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+# Help
+
+## Running the tests
+
+A `Makefile` is provided with a default target to compile your solution and run the tests. At the command line in your exercise's directory, type:
+
+```bash
+make
+```
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit leap.ml` 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 [OCaml track's documentation](https://exercism.org/docs/tracks/ocaml)
+- The [OCaml track's programming category on the forum](https://forum.exercism.org/c/programming/ocaml)
+- [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:
+
+- [Documentation for the Standard Library](http://caml.inria.fr/pub/docs/manual-ocaml/libref/index.html)
+- [/r/ocaml](https://www.reddit.com/r/ocaml) is the OCaml subreddit.
+- [StackOverflow](http://stackoverflow.com/questions/tagged/ocaml) can be used to search for your problem and see if it has been answered already. You can also ask and answer questions.

leap/Makefile

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+default: clean test
+
+test: 
+	dune runtest
+
+clean:
+	dune clean
+
+.PHONY: clean

leap/README.md

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+# Leap
+
+Welcome to Leap on Exercism's OCaml Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+Given a year, report if it is a leap year.
+
+The tricky thing here is that a leap year in the Gregorian calendar occurs:
+
+```text
+on every year that is evenly divisible by 4
+  except every year that is evenly divisible by 100
+    unless the year is also evenly divisible by 400
+```
+
+For example, 1997 is not a leap year, but 1996 is.
+1900 is not a leap year, but 2000 is.
+
+## Notes
+
+Though our exercise adopts some very simple rules, there is more to learn!
+
+For a delightful, four minute explanation of the whole leap year phenomenon, go watch [this youtube video][video].
+
+[video]: https://www.youtube.com/watch?v=xX96xng7sAE
+
+## Source
+
+### Created by
+
+- @tmcgilchrist
+
+### Contributed to by
+
+- @daveyarwood
+- @dvberkel
+- @iHiD
+- @ismaelga
+- @kytrinyx
+- @marionebl
+- @Peaupote
+- @pminten
+- @sbl
+- @sshine
+- @stevejb71
+
+### Based on
+
+CodeRanch Cattle Drive, Assignment 3 - https://coderanch.com/t/718816/Leap

leap/dune

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+(executable
+ (name test)
+ (libraries base ounit2))
+
+(alias
+  (name    runtest)
+  (deps    (:x test.exe))
+  (action  (run %{x})))
+
+(alias
+  (name    buildtest)
+  (deps    (:x test.exe)))
+
+(env
+  (dev
+    (flags (:standard -warn-error -A))))

leap/dune-project

@@ -0,0 +1 @@
+(lang dune 1.1)

leap/leap.ml

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+let leap_year year = 
+    (year mod 4 = 0 && year mod 100 <> 0) || year mod 400 = 0 

leap/leap.mli

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+val leap_year: int -> bool

leap/test.ml

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+open OUnit2
+open Leap
+
+let ae exp got _test_ctxt = assert_equal exp got ~printer:string_of_bool
+
+let tests = [
+  "year not divisible by 4 in common year" >::
+  ae false (leap_year 2015);
+  "year divisible by 2, not divisible by 4 in common year" >::
+  ae false (leap_year 1970);
+  "year divisible by 4, not divisible by 100 in leap year" >::
+  ae true (leap_year 1996);
+  "year divisible by 4 and 5 is still a leap year" >::
+  ae true (leap_year 1960);
+  "year divisible by 100, not divisible by 400 in common year" >::
+  ae false (leap_year 2100);
+  "year divisible by 100 but not by 3 is still not a leap year" >::
+  ae false (leap_year 1900);
+  "year divisible by 400 is leap year" >::
+  ae true (leap_year 2000);
+  "year divisible by 400 but not by 125 is still a leap year" >::
+  ae true (leap_year 2400);
+  "year divisible by 200, not divisible by 400 in common year" >::
+  ae false (leap_year 1800);
+]
+
+let () =
+  run_test_tt_main ("leap tests" >::: tests)