From 0e7b79026d14f066c9d90a6f385e95f14d584a82 Mon Sep 17 00:00:00 2001
From: John David Pressman <jd@jdpressman.com>
Date: Wed, 1 Jan 2020 12:30:55 -0800
Subject: [PATCH] Add docs page for loops

---
 gitlab-pages/docs/language-basics/loops.md | 87 ++++++++++++++++++++++
 gitlab-pages/website/sidebars.json         |  1 +
 2 files changed, 88 insertions(+)
 create mode 100644 gitlab-pages/docs/language-basics/loops.md

diff --git a/gitlab-pages/docs/language-basics/loops.md b/gitlab-pages/docs/language-basics/loops.md
new file mode 100644
index 000000000..6ac382fe5
--- /dev/null
+++ b/gitlab-pages/docs/language-basics/loops.md
@@ -0,0 +1,87 @@
+---
+id: loops
+title: Loops
+---
+
+
+
+## While Loop
+
+<!--DOCUSAURUS_CODE_TABS-->
+
+<!--Pascaligo-->
+
+The PascaLIGO while loop should look familiar to users of imperative languages. 
+While loops are of the form `while <condition clause> <block>`, and evaluate
+their associated block until the condition evaluates to false.
+
+> ⚠️ The current PascaLIGO while loop has semantics that have diverged from other LIGO syntaxes. The goal of LIGO is that the various syntaxes express the same semantics, so this will be corrected in future versions. For details on how loops will likely work after refactoring, see the CameLIGO tab of this example.
+
+```pascaligo
+function while_sum (var n : nat) : nat is block {
+  var i : nat := 0n ;
+  var r : nat := 0n ;
+  while i < n block {
+    i := i + 1n;
+    r := r + i;
+  }
+} with r
+```
+
+<!--CameLIGO-->
+
+`Loop.fold_while` is a fold operation that takes an initial value of a certain type
+and then iterates on it until a condition is reached. The auxillary function
+that does the fold returns either boolean true or boolean false to indicate
+whether the fold should continue or not. The initial value must match the input
+parameter of the auxillary function, and the auxillary should return type `(bool * input)`.
+
+```cameligo
+let aux (i: int) : bool * int =
+  if i < 100 then continue (i + 1) else stop i
+
+let counter_simple (n: int) : int =
+  Loop.fold_while aux_simple n
+```
+
+<!--END_DOCUSAURUS_CODE_TABS-->
+
+## For Loop
+
+<!--DOCUSAURUS_CODE_TABS-->
+<!--Pascaligo-->
+
+To iterate over a range of integers you use a loop of the form `for <variable assignment> to <integer> <block>`.
+
+```pascaligo
+function for_sum (var n : nat) : int is block {
+  var acc : int := 0 ;
+  for i := 1 to int(n)
+    begin
+      acc := acc + i;
+    end
+} with acc
+```
+
+<!--END_DOCUSAURUS_CODE_TABS-->
+
+<!--DOCUSAURUS_CODE_TABS-->
+<!--Pascaligo-->
+
+PascaLIGO for loops can also iterate through the contents of a collection. This is
+done with a loop of the form `for <element var> in <collection type> <collection var> <block>`.
+
+```pascaligo
+function for_collection_list (var nee : unit) : (int * string) is block {
+  var acc : int := 0;
+  var st : string := "to";
+  var mylist : list(int) := list 1; 1; 1 end;
+  for x in list mylist
+    begin
+      acc := acc + x;
+      st := st ^ "to";
+    end
+} with (acc, st)
+```
+
+<!--END_DOCUSAURUS_CODE_TABS-->
diff --git a/gitlab-pages/website/sidebars.json b/gitlab-pages/website/sidebars.json
index 13ce03e4e..4c5017e56 100644
--- a/gitlab-pages/website/sidebars.json
+++ b/gitlab-pages/website/sidebars.json
@@ -8,6 +8,7 @@
       "language-basics/strings",
       "language-basics/functions",
       "language-basics/boolean-if-else",
+      "language-basics/loops",
       "language-basics/unit-option-pattern-matching",
       "language-basics/maps-records",
       "language-basics/sets-lists-touples"