From 9c4adbc5a7bd96fe0ac4a5388114cfcf767165d4 Mon Sep 17 00:00:00 2001
From: Sergey Bronnikov <estetus@gmail.com>
Date: Tue, 18 Jun 2024 13:59:36 +0300
Subject: [PATCH] molly: add a log iterator

The patch add a generator which, when asked for an operation, logs
a message and yields `nil`.
---
 CHANGELOG.md   |  1 +
 molly/gen.lua  | 24 +++++++++++++++++++-----
 test/tests.lua |  9 ++++++++-
 3 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index dda991b..3fffdc8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- A `log()` iterator.
 - A `mix()` iterator.
 - A CAS-register generator.
 
diff --git a/molly/gen.lua b/molly/gen.lua
index 943ec8d..c82236b 100644
--- a/molly/gen.lua
+++ b/molly/gen.lua
@@ -38,6 +38,7 @@
 
 local fun = require('fun')
 local clock = require('molly.clock')
+local log = require('molly.log')
 local tbl = require('molly.compat.tbl')
 
 local fun_mt = debug.getmetatable(fun.range(10))
@@ -456,15 +457,28 @@ methods.flip_flop = flip_flop
 --- Special generators
 -- @section
 
---- (TODO) A generator which, when asked for an operation, logs a message and yields
---  nil. Occurs only once; use `repeat` to repeat.
+--- A generator which, when asked for an operation, logs
+-- a message and yields `nil`. Occurs only once; use `repeat` to
+-- repeat.
 -- @return an iterator
 --
+-- @usage
+-- > molly.gen.iter({1, 2, 3}):log()
+-- [INFO  2024-07-07 11:38:47:119933]: 1
+-- ---
+-- - null
+-- ...
+-- --
 -- @function log
-local log = function()
-    -- TODO
+local log_it = function(it)
+    assert(tostring(it) == '<generator>')
+    local gen, param, state = unwrap(it)
+    local _, v = gen(param, state)
+    log.info(v)
+    return nil_gen(nil, nil)
 end
-exports.log = log
+exports.log = log_it
+methods.log = log_it
 
 --- (TODO) Operations from that generator are scheduled at uniformly random intervals
 -- between `0` to `2 * (dt seconds)`.
diff --git a/test/tests.lua b/test/tests.lua
index b9cd18c..0d41f83 100644
--- a/test/tests.lua
+++ b/test/tests.lua
@@ -27,7 +27,7 @@ local utils = molly.utils
 local seed = os.time()
 math.randomseed(seed)
 
-test:plan(12)
+test:plan(13)
 
 test:test('clock', function(test)
     test:plan(5)
@@ -226,6 +226,13 @@ test:test('gen.mix', function(test)
     test:is(#tbl, 11, 'length of items generated by gen.mix')
 end)
 
+test:test('gen.log', function(test)
+    test:plan(1)
+
+    local res = molly.gen.iter({1, 2, 3}):log()
+    test:is(res, nil, 'gen.log returns nil')
+end)
+
 test:test('runner', function(test)
     test:plan(4)