Add binary-search exercise (#175)

config.json

@@ -452,6 +452,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 6
+      },
+      {
+        "slug": "binary-search",
+        "name": "Binary Search",
+        "uuid": "f171fdeb-ad29-4268-a3bf-0fd84380630b",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
       }
     ]
   },

exercises/practice/binary-search/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+Your task is to implement a binary search algorithm.
+
+A binary search algorithm finds an item in a list by repeatedly splitting it in half, only keeping the half which contains the item we're looking for.
+It allows us to quickly narrow down the possible locations of our item until we find it, or until we've eliminated all possible locations.
+
+~~~~exercism/caution
+Binary search only works when a list has been sorted.
+~~~~
+
+The algorithm looks like this:
+
+- Find the middle element of a _sorted_ list and compare it with the item we're looking for.
+- If the middle element is our item, then we're done!
+- If the middle element is greater than our item, we can eliminate that element and all the elements **after** it.
+- If the middle element is less than our item, we can eliminate that element and all the elements **before** it.
+- If every element of the list has been eliminated then the item is not in the list.
+- Otherwise, repeat the process on the part of the list that has not been eliminated.
+
+Here's an example:
+
+Let's say we're looking for the number 23 in the following sorted list: `[4, 8, 12, 16, 23, 28, 32]`.
+
+- We start by comparing 23 with the middle element, 16.
+- Since 23 is greater than 16, we can eliminate the left half of the list, leaving us with `[23, 28, 32]`.
+- We then compare 23 with the new middle element, 28.
+- Since 23 is less than 28, we can eliminate the right half of the list: `[23]`.
+- We've found our item.

exercises/practice/binary-search/.docs/introduction.md

@@ -0,0 +1,13 @@
+# Introduction
+
+You have stumbled upon a group of mathematicians who are also singer-songwriters.
+They have written a song for each of their favorite numbers, and, as you can imagine, they have a lot of favorite numbers (like [0][zero] or [73][seventy-three] or [6174][kaprekars-constant]).
+
+You are curious to hear the song for your favorite number, but with so many songs to wade through, finding the right song could take a while.
+Fortunately, they have organized their songs in a playlist sorted by the title — which is simply the number that the song is about.
+
+You realize that you can use a binary search algorithm to quickly find a song given the title.
+
+[zero]: https://en.wikipedia.org/wiki/0
+[seventy-three]: https://en.wikipedia.org/wiki/73_(number)
+[kaprekars-constant]: https://en.wikipedia.org/wiki/6174_(number)

exercises/practice/binary-search/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "erikschierboom"
+  ],
+  "files": {
+    "solution": [
+      "binary-search.8th"
+    ],
+    "test": [
+      "test.8th"
+    ],
+    "example": [
+      ".meta/example.8th"
+    ]
+  },
+  "blurb": "Implement a binary search algorithm.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Binary_search_algorithm"
+}

exercises/practice/binary-search/.meta/example.8th

@@ -0,0 +1,16 @@
+: middle \ n n - n
+  n:+ 2 n:/mod nip
+;
+
+: find-recur \ a n n n -- n
+  >r 
+  2dup n:> if 3drop null ;then
+  3dup middle a:_@
+  dup r@ n:= if drop middle nip ;then
+  dup r@ n:> if drop 2dup middle n:1- nip r> recurse ;then
+  drop 2dup middle n:1+ -rot nip r> recurse
+;
+
+: find \ a n -- n
+  >r a:len n:1- 0 swap r> find-recur
+;

exercises/practice/binary-search/.meta/tests.toml

@@ -0,0 +1,43 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[b55c24a9-a98d-4379-a08c-2adcf8ebeee8]
+description = "finds a value in an array with one element"
+
+[73469346-b0a0-4011-89bf-989e443d503d]
+description = "finds a value in the middle of an array"
+
+[327bc482-ab85-424e-a724-fb4658e66ddb]
+description = "finds a value at the beginning of an array"
+
+[f9f94b16-fe5e-472c-85ea-c513804c7d59]
+description = "finds a value at the end of an array"
+
+[f0068905-26e3-4342-856d-ad153cadb338]
+description = "finds a value in an array of odd length"
+
+[fc316b12-c8b3-4f5e-9e89-532b3389de8c]
+description = "finds a value in an array of even length"
+
+[da7db20a-354f-49f7-a6a1-650a54998aa6]
+description = "identifies that a value is not included in the array"
+
+[95d869ff-3daf-4c79-b622-6e805c675f97]
+description = "a value smaller than the array's smallest value is not found"
+
+[8b24ef45-6e51-4a94-9eac-c2bf38fdb0ba]
+description = "a value larger than the array's largest value is not found"
+
+[f439a0fa-cf42-4262-8ad1-64bf41ce566a]
+description = "nothing is found in an empty array"
+
+[2c353967-b56d-40b8-acff-ce43115eed64]
+description = "nothing is found when the left and right bounds cross"

exercises/practice/binary-search/binary-search.8th

@@ -0,0 +1,3 @@
+: find \ a n -- n
+
+;

exercises/practice/binary-search/libs/exercism/test

@@ -0,0 +1,173 @@
+needs console/loaded
+
+\ -----------------------------------------------------------------
+
+ns: test
+
+-1 var, test-count
+var tests-passed
+var tests-failed
+var tests-skipped
+true var, run-test
+
+\ Some utility words
+
+
+: test-passed \ s x x --   \\ test name, expected value, actual value
+    2drop
+    1 tests-passed n:+!
+    con:green con:onBlack . space " ... OK" . con:white con:onBlack cr
+;
+
+: test-skipped \ s --
+    1 tests-skipped n:+!
+    con:cyan con:onBlack . space " ... SKIPPED" . con:white con:onBlack cr
+;
+
+: test-failed \ s x x --   \\ test name, expected value, actual value
+    1 tests-failed n:+!
+    rot
+    con:red con:onBlack . space " ... FAIL" . con:white con:onBlack cr
+    "    Actual:    «" . . "»" . cr
+    "    Expected:  «" . . "»" . cr cr
+;
+
+: isword?  \ x -- x f
+   dup  >kind  ns:w   n:= 
+;
+
+: run-test? \ -- T
+   run-test @ if true else "RUN_ALL_TESTS" getenv n:>bool then
+;
+
+\ Num passed + num skipped + num failed should == num tests
+: all-tests-run? \ -- T
+    tests-passed @ tests-skipped @ tests-failed @ n:+ n:+
+    test-count @ n:=
+;
+
+\ returns true if x is a date, false otherwise
+: date? \ x -- x T
+    dup >kind ns:d n:=
+;
+
+\ adapted from 8th forum -- https://8th-dev.com/forum/index.php/topic,2745.0.html
+: eq? \ x x -- T
+   \ are the items the same kind?
+   2dup >kind swap >kind n:=
+   !if 2drop false ;then
+
+   \ same kind: try different comparators
+   number? if n:= ;then
+   string? if s:= ;then
+   array?  if ' eq? a:= 2nip ;then
+   map?    if ' eq? m:= 2nip ;then
+   date?   if d:= ;then
+
+   \ otherwise fall back to 'lazy evaluation'
+   l: =
+;
+
+: eps_eq? \ n x x -- T
+   \ are the items the same kind?
+   2dup >kind swap >kind n:=
+   !if 2drop false ;then
+   number? !if 2drop false ;then  
+   rot n:~=
+;
+
+: check-depth \ ... n -- ...
+  dup>r
+  n:1+ depth n:=
+  !if
+    con:red con:onBlack 
+    "PANIC: expected stack depth to be " . r> . cr
+    "Stack is:" . cr
+    .s cr
+    255 die
+  then
+  rdrop
+;
+
+\ -----------------------------------------------------------------
+
+\ status report at end of run
+( all-tests-run?  
+  !if con:red con:onBlack "... FAIL - not all tests completed" . con:white con:onBlack cr then
+) onexit
+
+\ Print a summary of the tests run
+( con:white con:onBlack
+  test-count   @ . space "tests planned - " .
+  tests-passed @ . space "passed - " .
+  tests-skipped @ . space "skipped - " .
+  tests-failed @ . space "failed" . cr
+) onexit
+
+\ -----------------------------------------------------------------
+\ The public-facing words
+\ -----------------------------------------------------------------
+    
+: equal? \ s x w -- | s w x --
+   run-test? !if 2drop test-skipped ;; then
+   isword? !if swap then
+   w:exec
+   3 check-depth
+   2dup             \ so test-failed can show actual and expected
+   eq? if test-passed else test-failed then
+;
+
+: approx_equal? \ s x w n -- | s w x n --
+   run-test? !if 3drop test-skipped ;; then
+   -rot isword? !if swap then
+   w:exec
+   4 check-depth
+   3dup            \ so test-failed can show actual and expected
+   eps_eq?
+   if rot drop test-passed else rot drop test-failed then
+;
+
+: true? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   true swap dup    \ so test-failed can show actual and expected
+   if test-passed else test-failed then 
+;
+
+: false? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   false swap dup    \ so test-failed can show actual and expected
+   !if test-passed else test-failed then 
+;
+
+: null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? nip if test-passed else test-failed then 
+;
+
+: SKIP-REST-OF-TESTS false run-test ! ;
+
+: tests \ n -- 
+    test-count ! 
+;
+
+\ Set the exit status:
+\   0 = all OK
+\   1 = not all tests were run (some error occurred)
+\   2 = some tests failed
+: end-of-tests \ --
+    all-tests-run?
+    if
+      tests-failed @ 0 n:= if 0 else 2 then
+    else
+      1
+    then
+    die
+;
+

exercises/practice/binary-search/test.8th

@@ -0,0 +1,59 @@
+"binary-search.8th" f:include
+needs exercism/test
+with: test
+11 tests
+
+"finds a value in an array with one element"
+    ( [6] 6 find )
+    0
+    equal?
+
+SKIP-REST-OF-TESTS
+
+"finds a value in the middle of an array"
+    ( [1, 3, 4, 6, 8, 9, 11] 6 find )
+    3
+    equal?
+
+"finds a value at the beginning of an array"
+    ( [1, 3, 4, 6, 8, 9, 11] 1 find )
+    0
+    equal?
+
+"finds a value at the end of an array"
+    ( [1, 3, 4, 6, 8, 9, 11] 11 find )
+    6
+    equal?
+
+"finds a value in an array of odd length"
+    ( [1, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 634] 144 find )
+    9
+    equal?
+
+"finds a value in an array of even length"
+    ( [1, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377] 21 find )
+    5
+    equal?
+
+"identifies that a value is not included in the array"
+    ( [1, 3, 4, 6, 8, 9, 11] 7 find )
+    null?
+
+"a value smaller than the array's smallest value is not found"
+    ( [1, 3, 4, 6, 8, 9, 11] 0 find )
+    null?
+
+"a value larger than the array's largest value is not found"
+    ( [1, 3, 4, 6, 8, 9, 11] 13 find )
+    null?
+
+"nothing is found in an empty array"
+    ( [] 1 find )
+    null?
+
+"nothing is found when the left and right bounds cross"
+    ( [1, 2] 0 find )
+    null?
+
+end-of-tests
+;with