add sieve exercise (exercism#205)

config.json

@@ -540,6 +540,14 @@
         ],
         "prerequisites": [],
         "difficulty": 5
+      },
+      {
+        "slug": "sieve",
+        "name": "Sieve",
+        "uuid": "5f29c607-3d50-476b-967a-5c54b65402aa",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
       }
     ],
     "foregone": [

exercises/practice/sieve/.docs/instructions.md

@@ -0,0 +1,42 @@
+# Instructions
+
+Your task is to create a program that implements the Sieve of Eratosthenes algorithm to find all prime numbers less than or equal to a given number.
+
+A prime number is a number larger than 1 that is only divisible by 1 and itself.
+For example, 2, 3, 5, 7, 11, and 13 are prime numbers.
+By contrast, 6 is _not_ a prime number as it not only divisible by 1 and itself, but also by 2 and 3.
+
+To use the Sieve of Eratosthenes, you first create a list of all the numbers between 2 and your given number.
+Then you repeat the following steps:
+
+1. Find the next unmarked number in your list (skipping over marked numbers).
+   This is a prime number.
+2. Mark all the multiples of that prime number as **not** prime.
+
+You keep repeating these steps until you've gone through every number in your list.
+At the end, all the unmarked numbers are prime.
+
+~~~~exercism/note
+The tests don't check that you've implemented the algorithm, only that you've come up with the correct list of primes.
+To check you are implementing the Sieve correctly, a good first test is to check that you do not use division or remainder operations.
+~~~~
+
+## Example
+
+Let's say you're finding the primes less than or equal to 10.
+
+- List out 2, 3, 4, 5, 6, 7, 8, 9, 10, leaving them all unmarked.
+- 2 is unmarked and is therefore a prime.
+  Mark 4, 6, 8 and 10 as "not prime".
+- 3 is unmarked and is therefore a prime.
+  Mark 6 and 9 as not prime _(marking 6 is optional - as it's already been marked)_.
+- 4 is marked as "not prime", so we skip over it.
+- 5 is unmarked and is therefore a prime.
+  Mark 10 as not prime _(optional - as it's already been marked)_.
+- 6 is marked as "not prime", so we skip over it.
+- 7 is unmarked and is therefore a prime.
+- 8 is marked as "not prime", so we skip over it.
+- 9 is marked as "not prime", so we skip over it.
+- 10 is marked as "not prime", so we stop as there are no more numbers to check.
+
+You've examined all numbers and found 2, 3, 5, and 7 are still unmarked, which means they're the primes less than or equal to 10.

exercises/practice/sieve/.docs/introduction.md

@@ -0,0 +1,7 @@
+# Introduction
+
+You bought a big box of random computer parts at a garage sale.
+You've started putting the parts together to build custom computers.
+
+You want to test the performance of different combinations of parts, and decide to create your own benchmarking program to see how your computers compare.
+You choose the famous "Sieve of Eratosthenes" algorithm, an ancient algorithm, but one that should push your computers to the limits.

exercises/practice/sieve/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "glennj"
+  ],
+  "files": {
+    "solution": [
+      "sieve.arr"
+    ],
+    "test": [
+      "sieve-test.arr"
+    ],
+    "example": [
+      ".meta/example.arr"
+    ]
+  },
+  "blurb": "Use the Sieve of Eratosthenes to find all the primes from 2 up to a given number.",
+  "source": "Sieve of Eratosthenes at Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes"
+}

exercises/practice/sieve/.meta/example.arr

@@ -0,0 +1,28 @@
+use context essentials2020 # Don't delete this line when using Pyret on Exercism 
+
+provide: primes end
+
+fun primes(limit) block:
+  marks = array-of(true, limit + 1)
+
+  var ps = [list:]
+  for each(i from range(2, limit + 1)):
+    when marks.get-now(i) block:
+      ps := ps.push(i)
+      mark-multiples(marks, i, limit)
+    end
+  end
+
+  ps.reverse()
+end
+
+fun mark-multiples(a :: Array<Boolean>, prime :: NumInteger, limit :: NumPositive):
+  rec do-mark = lam(i):
+    when i <= limit block:
+      a.set-now(i, false)
+      do-mark(i + prime)
+    end
+  end
+
+  do-mark(prime * prime)
+end

exercises/practice/sieve/.meta/tests.toml

@@ -0,0 +1,25 @@
+# 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.
+
+[88529125-c4ce-43cc-bb36-1eb4ddd7b44f]
+description = "no primes under two"
+
+[4afe9474-c705-4477-9923-840e1024cc2b]
+description = "find first prime"
+
+[974945d8-8cd9-4f00-9463-7d813c7f17b7]
+description = "find primes up to 10"
+
+[2e2417b7-3f3a-452a-8594-b9af08af6d82]
+description = "limit is prime"
+
+[92102a05-4c7c-47de-9ed0-b7d5fcd00f21]
+description = "find primes up to 1000"

exercises/practice/sieve/sieve-test.arr

@@ -0,0 +1,68 @@
+use context essentials2020
+
+include file("sieve.arr")
+
+#|
+  When working offline, all tests except the first one are skipped by default.
+  Once you get the first test running, unskip the next one until all tests pass locally.
+  Check the block comment below for further details.
+|#
+
+fun no-primes-under-two():
+  check "no primes under two":
+    primes(1) is [list:]
+  end
+end
+
+ fun find-first-prime():
+  check "find first prime":
+    primes(2) is [list:2]
+  end
+end
+
+fun find-primes-up-to-10():
+  check "find primes up to 10":
+    primes(10) is [list:2, 3, 5, 7]
+  end
+end
+
+fun limit-is-prime():
+  check "limit is prime":
+    primes(13) is [list:2, 3, 5, 7, 11, 13]
+  end
+end
+
+fun find-primes-up-to-1000():
+  check "find primes up to 1000":
+    primes(1000) is [list:
+          2,   3,   5,   7,  11,  13,  17,  19,  23,  29,  31,  37,  41,  43,
+         47,  53,  59,  61,  67,  71,  73,  79,  83,  89,  97, 101, 103, 107,
+        109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181,
+        191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263,
+        269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349,
+        353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431, 433,
+        439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509, 521,
+        523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607, 613,
+        617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701,
+        709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797, 809,
+        811, 821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887,
+        907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997
+    ]
+  end
+end
+
+#|
+  Code to run each test. Each line corresponds to a test above and whether it should be run.
+  To mark a test to be run, replace `false` with `true` on that same line after the comma.
+  test(test-a, true) will be run. test(test-a, false) will be skipped.
+|#
+
+data TestRun: test(run, active) end
+
+[list: 
+  test(no-primes-under-two, true),
+  test(find-first-prime, false),
+  test(find-primes-up-to-10, false),
+  test(limit-is-prime, false),
+  test(find-primes-up-to-1000, false),
+].each(lam(t): when t.active: t.run() end end)

exercises/practice/sieve/sieve.arr

@@ -0,0 +1,7 @@
+use context essentials2020 # Don't delete this line when using Pyret on Exercism 
+
+provide: primes end
+
+fun primes(limit):
+  raise("Please implement the primes function")
+end