add new animals example (that uses a pointer tree)

compiler/test/TestCompilerOnExamples.kt

@@ -238,6 +238,7 @@ class TestCompilerOnExamplesVirtual: FunSpec({
 
     val onlyVirtual = cartesianProduct(
         listOf(
+            "animals",                  // TODO move to root of examples later (and compile with c64 too)
             "bouncegfx",
             "bsieve",
             "pixelshader",

docs/source/todo.rst

@@ -1,6 +1,7 @@
 TODO
 ====
 
+
 STRUCTS and TYPED POINTERS
 --------------------------
 
@@ -56,6 +57,7 @@ STRUCTS and TYPED POINTERS
 - DONE: allow  list1^^ = list2^^  (value wise assignment of List structures) by replacing it with a sys.memcopy(list2, list1, sizeof(List)) call.
 - DONE: allow  a.b.ptr[i].value  (equiv to a.b.ptr[i]^^.value)  expressions  (assignment target doesn't parse yet, see below)
 - DONE: check passing arrays to typed ptr sub-parameters.  NOTE: word array can only be a @nosplit array if the parameter type is ^^word, because the words need to be sequential in memory there
+- allow str assign to ^^ubyte without cast (take address)
 - fix support for (expression) array index dereferencing "barray[2]^^"   where barray is ^^bool[10]
 - fix support for (assigntarget) array index dereferencing "barray[2]^^"   where barray is ^^bool[10]
 - fix support for (assigntarget) array index dereferencing "array[2].value"   where array is struct pointers

examples/virtual/animals.p8

@@ -0,0 +1,136 @@
+%import textio
+%import strings
+
+; Animal guessing game where the computer gets smarter every time.
+; Note: this program can be compiled for multiple target systems.
+; TODO: move this to examples/animals.p8 once it compiles for 6502 too
+
+main {
+
+    str userinput = "x"*80      ; buffer for user input
+
+    sub start() {
+        db.init()
+
+        txt.lowercase()
+        intro()
+
+         ^^db.Node active = db.first
+
+        ; the game loop asks questions and navigates the y/n tree of animals.
+        ; if an animal node is found, that animal could be the answer.
+        ; if it's not correct, a new question and the animal are inserted at that position in the tree.
+        repeat {
+            if active.question!=0 {
+                txt.print(active.question)
+                txt.print("? ")
+
+                if ask_yes_no()=='y'
+                    active = active.positive
+                else
+                    active = active.negative
+            } else {
+                txt.print("Is it a ")
+                txt.print(active.animal)
+                txt.print("? ")
+
+                if ask_yes_no()=='y' {
+                    txt.print("\nYay, I knew it!\n")
+                    txt.print("Let's go for another round.\n\n")
+                }
+                else
+                    learn_new_animal()
+
+                active = db.first
+                intro()
+            }
+        }
+
+        sub intro() {
+            txt.print("Hello. Please think of an animal.\n")
+            txt.print("I will try to guess what it is!\n\n")
+        }
+
+        sub ask_yes_no() -> ubyte {
+            repeat {
+                if txt.input_chars(userinput)!=0 {
+                    txt.nl()
+                    if userinput[0]=='y' or userinput[0]=='n'
+                        return userinput[0]
+                    txt.print("Please answer yes or no.\n")
+                } else {
+                    txt.nl()
+                }
+            }
+        }
+
+        sub learn_new_animal() {
+            str new_animal = "x" * 30
+            str answer = "x" * 10
+            txt.print("\nI give up. What is the animal? ")
+            void txt.input_chars(new_animal)
+            txt.print("\nWhat yes/no question would best tell a ")
+            txt.print(new_animal)
+            txt.print(" apart from a ")
+            txt.print(active.animal)
+            txt.print("? ")
+            ubyte question_length = txt.input_chars(userinput)
+            uword question_addr = arena.alloc(question_length+1)
+            void strings.copy(userinput, question_addr)
+            txt.print("In case of the ")
+            txt.print(new_animal)
+            txt.print(", what is the answer to that question? ")
+            ubyte yesno = ask_yes_no()
+
+            ^^db.Node new_animal_node = db.Node(0, new_animal, 0, 0)
+            ^^db.Node wrong_animal_node = db.Node(0, 0, 0, 0)
+            wrong_animal_node.animal = active.animal
+            active.question = question_addr
+            active.animal = 0
+            if yesno=='y' {
+                active.positive = new_animal_node
+                active.negative = wrong_animal_node
+            } else {
+                active.positive = wrong_animal_node
+                active.negative = new_animal_node
+            }
+
+            txt.print("\nI've learned about that new animal now!\n")
+            txt.print("Let's go for another round.\n\n")
+        }
+    }
+}
+
+db {
+    struct Node {
+        str question
+        str animal
+        ^^Node negative
+        ^^Node positive
+    }
+
+    ^^Node first
+
+    sub init() {
+        first = Node("does it swim", 0, 0, 0)
+        ^^Node eagle = Node(0, "eagle", 0, 0)
+        ^^Node dolpin = Node(0, "dolpin", 0, 0)
+        ^^Node question = Node("can it fly", 0, 0, 0)
+        ^^Node horse = Node(0, "horse", 0, 0)
+        first.negative = question
+        first.positive = dolpin
+        question.negative = horse
+        question.positive = eagle
+    }
+}
+
+arena {
+    ; extremely trivial arena allocator (that never frees)
+    uword buffer = memory("arena", 10000, 0)
+    uword next = buffer
+
+    sub alloc(ubyte size) -> uword {
+        defer next += size
+        return next
+    }
+}