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--- at:tutorial:basic [2020/02/09 19:32] – elisag
+++ at:tutorial:basic [2020/02/09 21:47] – elisag
@@ Line 85: / Line 85: @@
 >>[2, 3, 4]
 </code>
@@ Line 101: / Line 107: @@
 >a[1]
 >>[1, 0, 0]
+>(a[1])[2] := 3;
+>>3
+>a
+>>[[1, 3, 0], [0, 1, 0], [0, 0, 1]]
 </code>
@@ Line 110: / Line 120: @@
 def b[3] { i := i + 1; aux := [0,0,0]; aux[i] :=1; aux};
 >>[[1, 0, 0], [0, 1, 0], [0, 0, 1]]
->b[1][2]
->>0
->(b[1])[2] := 3;
->>3
->b
->>[[1, 3, 0], [0, 1, 0], [0, 0, 1]]
 </code>
 ===== Functions =====
@@ Line 220: / Line 226: @@
 >> 21
 </code>
 ==== Optional Parameters ====
@@ Line 233: / Line 240: @@
 </code>
-As is customary in languages with the above parameter passing semantics, AmbientTalk requires mandatory parameters to be defined //before// optional parameters, which should in turn be defined //before// a variable-argument parameter, if any.
+As is customary in languages with the above optional arguments, AmbientTalk requires mandatory parameters to be defined //before// optional parameters, which should in turn be defined //before// a variable-argument parameter, if any.
+Let us show how to use optional arguments to define an auxilary function that creates matrices as follows:
+<code>
+def makeMatrix(n, m := n, init := { |i,j| 0}){
+  def [i,j] := [0,0];
+  def makeCol(i,j) {
+     def col[m] { j := j + 1; init(n,m) }
+  };
+  def matrix[n] { i := i + 1; makeCol(i,j)}
+};
+def b := makeMatrix(2,4, {|i,j| object: { def occupied := false }});
+>((b[2])[4]).occupied := true
+>>true
+>(h[2]).each: {|e| system.print(" " + e.occupied)}
+>> false false false true
+>def c := makeMatrix(3);
+>>[[0, 0, 0], [0, 0, 0], [0, 0, 0]]
+>c[1] := [1,2,3]
+>>[1, 2, 3]
+>c
+>>[[1, 2, 3], [0, 0, 0], [0, 0, 0]]
+</code>
 ===== Closures =====