Struct equality (actually more like "hash-consing") in stackmac.

README.md

@@ -703,6 +703,13 @@ Equality, inequality, boolean operators.
     | }
     = struth
 
+    | fun main() {
+    |   if "five" == "five" and (("six" != "seven") or false) {
+    |     print("struth")
+    |   }
+    | }
+    = struth
+
 Equality cannot be checked between two values of different types.
 
     | fun main() {
@@ -864,13 +871,42 @@ doesn't matter if this is structural equality or identity.)
     | }
     = True
 
-    /| struct person { age: integer; name: string }
-    /| main = fun() {
-    /|   j = make person(age: 23, name:"Jake");
-    /|   k = make person(age: 23, name:"John");
-    /|   j == k
-    /| }
-    /= False
+    | struct person { age: integer; name: string }
+    | main = fun() {
+    |   j = make person(age: 23, name:"Jake");
+    |   k = make person(age: 23, name:"John");
+    |   j == k
+    | }
+    = False
+
+    | struct person { age: integer; name: string }
+    | main = fun() {
+    |   j = make person(age: 23, name:"Jake");
+    |   k = make person(age: 21, name:"Jake");
+    |   j != k
+    | }
+    = True
+
+Structs of two different types cannot be tested for equality.
+
+    | struct person { age: integer; name: string }
+    | struct individual { age: integer; name: string }
+    | main = fun() {
+    |   j = make person(age: 23, name:"Jake");
+    |   k = make individual(age: 23, name:"Jake");
+    |   j == k
+    | }
+    ? mismatch
+
+Structs cannot be compared for ordering.
+
+    | struct person { age: integer; name: string }
+    | main = fun() {
+    |   j = make person(age: 23, name:"Jake");
+    |   k = make person(age: 21, name:"Jake");
+    |   j > k
+    | }
+    ? structs cannot be compared for order
 
 Structs can be passed to functions.
 

src/castile/checker.py

@@ -97,6 +97,8 @@ def type_of(self, ast):
                 type1 = self.type_of(ast.children[0])
                 type2 = self.type_of(ast.children[1])
                 self.assert_eq(type1, type2)
+                if ast.value in ('>', '>=', '<', '<=') and isinstance(type1, Struct):
+                    raise CastileTypeError("structs cannot be compared for order")
                 ast.type = Boolean()
         elif ast.tag == 'Not':
             type1 = self.type_of(ast.children[0])

src/castile/stackmac.py

@@ -20,6 +20,16 @@ def boo(b):
         return 0
 
 
+def add_string(strings, s):
+    """Adds a string to the pool, deduping it.  Returns the index of the
+    entry of the string, whether new or existing."""
+    for n, t in enumerate(strings):
+        if t == s:
+            return n
+    strings.append(s)
+    return len(strings) - 1
+
+
 def run(program, strings):
     global labels
     ip = 0
@@ -52,21 +62,21 @@ def run(program, strings):
                 elif name == 'concat':
                     b = strings[stack.pop()]
                     a = strings[stack.pop()]
-                    strings.append(builtin(a, b))
-                    stack.append(len(strings) - 1)
+                    pos = add_string(strings, builtin(a, b))
+                    stack.append(pos)
                 elif name == 'len':
                     a = strings[stack.pop()]
                     stack.append(builtin(a))
                 elif name == 'substr':
                     k = stack.pop()
                     p = stack.pop()
                     s = strings[stack.pop()]
-                    strings.append(builtin(s, p, k))
-                    stack.append(len(strings) - 1)
+                    pos = add_string(strings, builtin(s, p, k))
+                    stack.append(pos)
                 elif name == 'str':
                     n = stack.pop()
-                    strings.append(builtin(n))
-                    stack.append(len(strings) - 1)
+                    pos = add_string(strings, builtin(n))
+                    stack.append(pos)
                 else:
                     raise NotImplementedError(name)
         elif op == 'rts':
@@ -235,8 +245,7 @@ def main(args):
         else:
             match = re.match(r"^'(.*?)'$", arg)
             if match:
-                strings.append(match.group(1))
-                arg = len(strings) - 1
+                arg = add_string(strings, match.group(1))
             else:
                 arg = int(arg)
             p.append((op, arg))