From d450c057e45ed3937989e43894206e99ef4be7dc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?St=C3=A9phane=20Del=20Pino?= <stephane.delpino44@gmail.com>
Date: Mon, 30 May 2022 14:23:56 +0200
Subject: [PATCH] Describe for loops
---
doc/userdoc.org | 60 ++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 59 insertions(+), 1 deletion(-)
diff --git a/doc/userdoc.org b/doc/userdoc.org
index 95a577c9b..092dcc3d6 100644
--- a/doc/userdoc.org
+++ b/doc/userdoc.org
@@ -1878,7 +1878,65 @@ We give a final illustration
#+END_SRC
#+results: if-block
-*** TODO for loops
+*** ~for~ loops
+
+~pugs~ allow to write ~for~ loops. It follows the ~C++~ syntax
+#+BEGIN_SRC pugs :exports code
+ for (declarationinstruction ; condition ; postinstruction) statement
+#+END_SRC
+Following ~C++~, ~declarationinstruction~, ~condition~ and ~postinstruction~
+are optional. The ~condition~ argument if present *must* be a boolean
+value (type ~B~), if it is absent, the default value ~true~ is used.
+
+- The ~declarationinstruction~ is execute only *once* /before/ the beginning
+ of the loop. The lifetime of the variable declared here is defined
+ by the ~for~ instruction itself.
+
+- The ~condition~ is evaluate /before/ each loop.
+
+- The ~postinstruction~ is executed /after/ each loop.
+
+- The ~statement~ is either a single instruction or a block of
+ instructions. The ~statement~ is executed if the ~condition~ has the
+ value ~true~.
+
+For instance, one can write
+#+NAME: for-block
+#+BEGIN_SRC pugs :exports both :results output
+ let n:N, n = 10;
+ let sum:N, sum = 0;
+ for (let i:N, i=1; i<=n; ++i) {
+ sum += i;
+ }
+ cout << "sum = " << sum << "\n";
+#+END_SRC
+which gives as expected
+#+results: for-block
+
+The lifetime of the declared variable (in the ~declarationinstruction~
+statement) is illustrate by the following example
+#+NAME: for-scope-error
+#+BEGIN_SRC pugs-error :exports both :results output
+ for (let i:N, i=0; i<2; ++i) {
+ cout << "i = " << i << "\n";
+ }
+ cout << "i = " << i << "\n";
+#+END_SRC
+Running this example produces the following error
+#+results: for-scope-error
+
+To fix the previous code, one can write
+#+NAME: for-no-decl
+#+BEGIN_SRC pugs :exports both :results output
+ let i:N, i=0;
+ for (; i<2; ++i) {
+ cout << "i = " << i << "\n";
+ }
+ cout << "i = " << i << "\n";
+#+END_SRC
+One gets
+#+results: for-no-decl
+
*** TODO do while loops
--
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