eval + basic stdlib

repl.py

@@ -1,5 +1,4 @@
 import wasp
-import wasp.parser
 import readline
 
 
@@ -29,21 +28,20 @@ if __name__ == "__main__":
     # http://stackoverflow.com/questions/5637124
     #readline.set_completer(complete)
 
+    context = wasp.Context()
+
     for line in Reader(">> ", banner="WASP %s" % wasp.VERSION):
         if line == "" or line is None:
             continue
 
         try:
-            ptree = wasp.parser.parse(line)
-        except ValueError, e:
+            ast = context['read'](line)
+        except wasp.lib.ReadError, e:
             print "Parse error:", e.message
             continue
 
-        print " ^ %s" % ptree
         try:
-            ast = ptree.ast()
-        except ValueError, e:
-            print "AST error:", e.message
+            print context['eval'](ast, context)
+        except wasp.SymbolError, e:
+            print "Undefined symbol:", e.message
             continue
-        print " ‡ %r" % ast
-        #ast.eval()

test.py

@@ -40,6 +40,12 @@ class TestParser(TestCase):
         self.assertRaises(ValueError, parser.parse("(42"))
 
 
+class TestAST(TestCase):
+    def test_lists_in_list(self):
+        ptree = parser.parse("(+ (* 4 5) (* 3 2))")
+        repr(ptree.ast())
+
+
 if __name__ == '__main__':
     import unittest
     unittest.main()

wasp/__init__.py

@@ -1 +1,31 @@
+from __future__ import print_function
+
+
+import wasp.lib as lib
+
+
 VERSION = '0.0.1'
+
+
+class SymbolError(Exception):
+    pass
+
+
+class Context(object):
+    symbols = {
+        '+': lib.plus,
+        '-': lib.minus,
+        '*': lib.multiply,
+        '/': lib.div,
+        'read': lib.read,
+        'eval': lib.eval,
+        'print': lib.print,
+        'apply': lib.apply,
+        'quote': lib.quote,
+    }
+
+    def __getitem__(self, symbol):
+        try:
+            return self.symbols[symbol]
+        except KeyError:
+            raise SymbolError(symbol)

wasp/ast.py

@@ -7,8 +7,8 @@ class List(Node):
         self.car = car
         self.cdr = cdr
 
-    def eval(self):
-        pass
+    def eval(self, context):
+        return context['apply'](self.car, self.cdr, context)
 
     def __repr__(self):
         return "<List %r %r>" % (self.car, self.cdr)
@@ -26,7 +26,7 @@ class Number(Atom):
     def __init__(self, value):
         self.value = value
 
-    def eval(self):
+    def eval(self, context):
         return self.value
 
     def __repr__(self):
@@ -45,8 +45,8 @@ class Symbol(Atom):
     def __init__(self, value):
         self.value = value
 
-    def eval(self):
-        return self.value
+    def eval(self, context):
+        return context[self.value]
 
     def __repr__(self):
         return "<Symbol %s>" % self.value
@@ -56,7 +56,7 @@ class String(Atom):
     def __init__(self, value):
         self.value = value
 
-    def eval(self):
+    def eval(self, context):
         return self.value
 
     def __repr__(self):
@@ -67,8 +67,8 @@ class Quote(Node):
     def __init__(self, sexpr):
         self.sexpr = sexpr
 
-    def eval(self):
-        return self.sexpr.eval()
+    def eval(self, context):
+        return context['quote'](self.sexpr)
 
     def __repr__(self):
         return "<Quote %r>" % self.sexpr

wasp/lib.py

@@ -0,0 +1,64 @@
+from __future__ import print_function
+
+import wasp.parser
+
+
+py_print = print
+py_eval = eval
+
+
+class ReadError(Exception):
+    pass
+
+
+def plus(a, b):
+    return a + b
+
+
+def minus(a, b):
+    return a - b
+
+
+def multiply(a, b):
+    return a * b
+
+
+def div(a, b):
+    return a / b
+
+
+def read(string):
+    try:
+        ptree = wasp.parser.parse(string)
+    except ValueError, e:
+        raise ReadError(e.message)
+    py_print(" ^ %s" % ptree)
+
+    try:
+        ast = ptree.ast()
+    except ValueError, e:
+        raise ReadError(e.message)
+    py_print(" ‡ %r" % ast)
+
+    return ast
+
+
+def eval(ast, context):
+    # eval value unless list
+    # eval args unless lazy
+    # eval call
+    return ast.eval(context)
+
+
+def apply(a, b, context):
+    # move to eval
+    args = [arg.eval(context) for arg in b]
+    return a.eval(context)(*args)
+
+
+def quote(a):
+    return a
+
+
+def print(string):
+    py_print(string)