From 3d498c134a9c0ab61c86a233edd0b2eb76ef44eb Mon Sep 17 00:00:00 2001
From: stuebinm
Date: Tue, 20 Jul 2021 20:43:16 +0200
Subject: playing around with IO in Nix

---
 nix-turing/io.nix | 147 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 147 insertions(+)
 create mode 100644 nix-turing/io.nix

(limited to 'nix-turing/io.nix')

diff --git a/nix-turing/io.nix b/nix-turing/io.nix
new file mode 100644
index 0000000..7f904d6
--- /dev/null
+++ b/nix-turing/io.nix
@@ -0,0 +1,147 @@
+#
+# General purpose programming Nix: Plan of attack
+# ===============================================
+#
+#  1. define some nice attrset that all these functions
+#     pass to each other implicitely
+#  2. minimise unnecessary build output
+#  3. a monadic do notation taking a list of monad operations?
+#     (how to deal with variables?)
+#  4. implement tic tac toe
+#
+# TODO
+#  - nicer syntax
+#  - put this into a library
+#  - make the seed configurable via cli
+#  - tic tac toe
+# let
+{ s, ... }: rec {
+  pkgs = import <nixpkgs> {};
+
+  seed = toString s;
+  eval = code: import (pkgs.writeText "code" code);
+
+  pause = idx: prompt: pkgs.stdenv.mkDerivation {
+    name = "sleep-${seed}";
+    src = pkgs.hello;
+    phases = [ "buildPhase" ];
+    buildPhase = ''
+      echo
+      echo
+      echo ${pkgs.lib.escapeShellArg prompt}
+      sleep 2
+      echo waiting 3 ...
+      sleep 2
+      echo waiting 2 ...
+      sleep 2
+      echo waiting 1 ...
+      mkdir -p $out
+    '';
+  };
+
+  pause_and = { prev, idx, inputCounter, ... }: prompt: code: {
+    prev = pkgs.stdenv.mkDerivation {
+      name = "pause_and-${toString idx}";
+      buildInputs =  [ ( pause idx prompt ) ];
+      phases = [ "buildPhase" ];
+      src = pkgs.writeText "code" code;
+      buildPhase = ''
+      echo ${if prev != null then prev.outPath else ""}
+      # ${seed}
+      cp $src $out
+    '';
+    };
+    idx = idx;
+    inherit inputCounter;
+  };
+
+  read_input = prompt: realWorld:
+    let nextWorld = pause_and
+        realWorld
+        ''
+          ${prompt}
+          please enter your input in file /tmp/input-${toString realWorld.inputCounter}
+        ''
+        ''
+          with import <nixpkgs> {};
+          lib.readFile
+            "/tmp/input-${toString realWorld.inputCounter}"
+          # ${seed}
+          # ${if realWorld.prev != null
+              then realWorld.prev.outPath
+              else ""}
+        '';
+    in
+      {
+        prev = nextWorld.prev;
+        value = realWorld.value // {
+          input = import nextWorld.prev.outPath;
+        };
+        inputCounter = nextWorld.inputCounter + 1;
+        idx = nextWorld.idx + 1;
+      };
+
+  print = msg: realWorld: {
+    prev = pkgs.stdenv.mkDerivation {
+      name = "log-derivation";
+      phases = [ "print" ];
+      print = ''
+        echo ${pkgs.lib.escapeShellArg msg}
+        echo ${pkgs.lib.escapeShellArg msg} > $out
+        # ${toString realWorld.idx}
+        # ${seed}
+        # ${if realWorld.prev != null
+            then realWorld.prev.outPath
+            else ""}
+      '';
+    };
+    idx = realWorld.idx + 1;
+    inherit (realWorld) inputCounter value;
+  };
+
+  log = msg:
+    print "==============LOG===============\n${msg}";
+
+  initialWorld = {
+    prev = null;
+    idx = 0;
+    inputCounter = 0;
+    value = {};
+  };
+
+  call = realWorld:
+    realWorld.prev;
+
+  assign = name: value: realWorld:
+    realWorld // {value = realWorld.value // {${name} = value;};};
+
+  # the IO monad
+  bind = monadic: operation:
+    monadic // ((operation monadic.value) monadic);
+
+  bindMonadic = operation: monadic:
+    bind monadic operation;
+
+  unit = realWorld: realWorld;
+
+  # basic do notation
+  do = monadic: operations:
+    pkgs.lib.foldl bind monadic operations;
+
+  # flipped version of do for usage in bound
+  doMonadic = operations: monadic:
+    do monadic operations;
+
+  ifThenElse = cond: ifTrue: ifFalse:
+    (v: if cond v
+        then ifTrue v
+        else ifFalse v);
+
+  while = cond: body:
+    (ifThenElse cond
+      (v: doMonadic [
+        body
+        (while cond body)
+      ])
+      (v: unit));
+}
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