Implement str builtin in Ruby, JavaScript, and stackmac backends.

TODO.md

@@ -29,8 +29,6 @@ AST nodes should have source line numbers, it would be really nice.
 
 C backend.  Other backends (Python? Java? CIL? Scheme?)
 
-Runtime support for `str` in Ruby backend and JavaScript backend.
-
 ### Design ###
 
 Convenience:

src/castile/backends/javascript.py

@@ -36,6 +36,7 @@ def compile(self, ast):
 var len = function(s) { return s.length; };
 var concat = function(s1,s2) { return s1 + s2; };
 var substr = function(s,p,k) { return s.substr(p, k); };
+var str = function(n) { return '' + n; };
 
 var repr = function(o) {
   if (typeof o === "string") {

src/castile/backends/ruby.py

@@ -49,6 +49,10 @@ def compile(self, ast):
   s[p..p+(k-1)]
 }
 
+str = lambda { |n|
+  n.to_s
+}
+
 def repr o
   if o == true
     return "True"

src/castile/stackmac.py

@@ -63,6 +63,10 @@ def run(program, strings):
                     s = strings[stack.pop()]
                     strings.append(builtin(s, p, k))
                     stack.append(len(strings) - 1)
+                elif name == 'str':
+                    n = stack.pop()
+                    strings.append(builtin(n))
+                    stack.append(len(strings) - 1)
                 else:
                     raise NotImplementedError(name)
         elif op == 'rts':
@@ -233,4 +237,6 @@ def main(args):
                 arg = int(arg)
             p.append((op, arg))
 
+    if debug:
+        print(strings)
     run(p, strings)