[Alan] Add two correct and some erroneous programs, courtesy of Pantosx2

Author: kostis

alan/programs-erroneous/array_no_index.alan

@@ -0,0 +1,6 @@
+main() : proc
+   arr : int [10];
+   x : int;
+{
+   x = arr; -- Using array variable without an index
+}

alan/programs-erroneous/duplicate_variable.alan

@@ -0,0 +1,6 @@
+main() : proc
+   x : int;
+   x : int;   -- Redeclaring the variable 'x'
+{
+   x = 42;
+}

alan/programs-erroneous/incorrect_args.alan

@@ -0,0 +1,11 @@
+main() : proc
+
+   add (a: int, b: int) : int
+   {
+      return a + b;
+   }
+
+   result : int;
+{
+   result = add(42);   -- Missing one argument
+}

alan/programs-erroneous/nested_undefined_variable.alan

@@ -0,0 +1,14 @@
+main() : proc
+
+   outerFunction () : proc
+      innerFunction () : proc
+      {
+         y = 42;   -- 'y' is not declared in any accessible scope
+      }
+   {
+      innerFunction();
+   }
+
+{
+   outerFunction();
+}

alan/programs-erroneous/procedure_in_expression.alan

@@ -0,0 +1,11 @@
+main() : proc
+
+   printMessage () : proc
+   {
+      writeString("Hello\n");
+   }
+
+   x : int;
+{
+   x = printMessage() + 42;   -- Using a procedure in an expression
+}

alan/programs-erroneous/return_in_proc.alan

@@ -0,0 +1,10 @@
+main() : proc
+
+   printMessage () : proc
+   {
+      return 42;   -- Returning a value from a procedure, which is invalid
+   }
+
+{
+   printMessage();
+}

alan/programs-erroneous/type_mismatch.alan

@@ -0,0 +1,5 @@
+main() : proc
+   x : int;
+{
+   x = "hello";   -- Assigning string to an integer variable
+}

alan/programs-erroneous/undeclared_variable.alan

@@ -0,0 +1,4 @@
+main() : proc
+{
+   x = 42;   -- 'x' is undeclared
+}

alan/programs-erroneous/wrong_return_type.alan

@@ -0,0 +1,11 @@
+main() : proc
+
+   getValue () : int
+   {
+      return "string";   -- Returning a string instead of an integer
+   }
+
+   result : int;
+{
+   result = getValue();
+}

alan/programs/concat.alan

@@ -0,0 +1,28 @@
+main() : proc
+
+   concat (s1: reference byte [], s2: reference byte []) : proc
+      i : int;
+      l1 : int;
+      l2 : int;
+   {
+      l1 = strlen(s1);
+      l2 = strlen(s2);
+      i = 0;
+      while (i < l2) {
+         s1[l1+i] = s2[i];
+         i = i+1;
+      }
+      s1[l1+l2] = '\0';
+   }
+
+   str1 : byte [64];
+   str2 : byte [32];
+{
+   readString(64, str1);
+   readString(32, str2);
+
+   concat(str1, str2);
+
+   writeString(str1);
+   writeChar('\n');
+}