First revision of Arrays

content/arrays.md

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+---
+title: Arrays
+---
+
+# Arrays
+
+The arrays in Nimrod are like classic C arrays, their size is specified at compile-time and cannot given or changed at runtime.
+
+``` nimrod
+type
+  ThreeStringAddress = array[3, string]
+let names: ThreeStringAddress = ["Jasmine", "Ktisztina", "Kristof"]
+let addresses: ThreeStringAddress = ["101 Betburweg", "66 Bellion Drive", "194 Laarderweg"]
+```
+
+The size of the array is encoded in its type and cannot be accidentally lost. Therefore, a procedure taking an array of variable length must encode the length in its type parameters.
+
+``` nimrod
+proc zip[I, T](a, b: array[I, T]):
+               array[I, tuple[a, b: T]] =
+  for i in low(A)..high(A):
+    result[i] = (a[i], b[i])
+
+let nameAndAddresses = names.zip(addresses)
+```
+
+Alternate methods of indexing arrays are also allowed, the first type parameter is actually a range (just a value, as above, is syntactic sugar for `0..N-1`). It's also possible to use ordinal values to index an array, effectively creating a lookup table:
+
+``` nimrod
+type
+  PartsOfSpeech {.pure.} = enum
+    Pronoun, Verb, Article, Adjective, Noun, Adverb
+let partOfSpeechExamples: array[PartsOfSpeech] = [
+  "he", "reads", "the", "green", "book", "slowly"
+]
+```
+
+``` nimrod
+type
+  Matrix[W, H: static[int]] =
+    array[1..W, array[1..H, int]]
+
+let mat1: Matrix[2, 2] = [[1, 0],
+                          [0, 1]]
+let mat2: Matrix[2, 2] = [[0, 1],
+                          [1, 0]]
+
+proc `+`[W, H](a, b: Matrix[W, H]):
+               Matrix[W, H] =
+  for i in 1..high(a):
+    for j in 1..high(a[0]):
+      result[i][j] = a[i][j] + b[i][j]
+
+proc `$`[W, H](a: Matrix[W, H]): string =
+  result = ""
+  for v in a:
+    for vx in v:
+      result.add($vx & ", ")
+    result.add("\n")
+
+echo mat1 + mat2
+```
+
+``` console
+$ nimrod c -r matrix.nim
+1, 1, 
+1, 1, 
+
+```