feat: special forms

scheme_classes.py

@@ -1,6 +1,7 @@
 import builtins
 
 from pair import *
+from util import *
 
 class SchemeError(Exception):
     """Exception indicating an error in a Scheme program."""
@@ -54,7 +55,11 @@ def make_child_frame(self, formals, vals):
         if len(formals) != len(vals):
             raise SchemeError('Incorrect number of arguments to function call')
         # BEGIN PROBLEM 8
-        "*** YOUR CODE HERE ***"
+        formals = pair_to_list(formals)
+        vals = pair_to_list(vals)
+        new_frame = Frame(self)
+        map_(iota(len(formals)), lambda i: new_frame.define(formals[i], vals[i]))
+        return new_frame
         # END PROBLEM 8
 
 ##############

scheme_eval_apply.py

@@ -60,11 +60,13 @@ def scheme_apply(procedure, args, env):
             raise SchemeError('incorrect number of arguments: {0}'.format(procedure))
     elif isinstance(procedure, LambdaProcedure):
         # BEGIN PROBLEM 9
-        "*** YOUR CODE HERE ***"
+        new_frame = procedure.env.make_child_frame(procedure.formals, args)
+        return eval_all(procedure.body, new_frame)
         # END PROBLEM 9
     elif isinstance(procedure, MuProcedure):
         # BEGIN PROBLEM 11
-        "*** YOUR CODE HERE ***"
+        new_frame = env.make_child_frame(procedure.formals, args)
+        return eval_all(procedure.body, new_frame)
         # END PROBLEM 11
     else:
         assert False, "Unexpected procedure: {}".format(procedure)
@@ -85,7 +87,10 @@ def eval_all(expressions, env):
     2
     """
     # BEGIN PROBLEM 6
-    return scheme_eval(expressions.first, env) # replace this with lines of your own code
+    if expressions == nil:
+        return None
+    map_(except_last(expressions), lambda x: scheme_eval(x, env))
+    return scheme_eval(last(expressions), env)
     # END PROBLEM 6
 
 

scheme_forms.py

@@ -2,6 +2,7 @@
 from scheme_utils import *
 from scheme_classes import *
 from scheme_builtins import *
+from util import *
 
 #################
 # Special Forms #
@@ -36,12 +37,20 @@ def do_define_form(expressions, env):
         # assigning a name to a value e.g. (define x (+ 1 2))
         validate_form(expressions, 2, 2) # Checks that expressions is a list of length exactly 2
         # BEGIN PROBLEM 4
-        "*** YOUR CODE HERE ***"
+        expr = expressions.rest.first
+        val = scheme_eval(expr, env)
+        env.define(signature, val)
+        return signature
         # END PROBLEM 4
     elif isinstance(signature, Pair) and scheme_symbolp(signature.first):
         # defining a named procedure e.g. (define (f x y) (+ x y))
         # BEGIN PROBLEM 10
-        "*** YOUR CODE HERE ***"
+        symbol = signature.first
+        formals = signature.rest
+        body = expressions.rest
+        lambda_ = do_lambda_form(Pair(formals, body), env)
+        env.define(symbol, lambda_)
+        return symbol
         # END PROBLEM 10
     else:
         bad_signature = signature.first if isinstance(signature, Pair) else signature
@@ -56,7 +65,8 @@ def do_quote_form(expressions, env):
     """
     validate_form(expressions, 1, 1)
     # BEGIN PROBLEM 5
-    "*** YOUR CODE HERE ***"
+    quoted = expressions.first
+    return quoted
     # END PROBLEM 5
 
 def do_begin_form(expressions, env):
@@ -82,7 +92,8 @@ def do_lambda_form(expressions, env):
     formals = expressions.first
     validate_formals(formals)
     # BEGIN PROBLEM 7
-    "*** YOUR CODE HERE ***"
+    body =  expressions.rest
+    return LambdaProcedure(formals, body, env)
     # END PROBLEM 7
 
 def do_if_form(expressions, env):
@@ -115,7 +126,14 @@ def do_and_form(expressions, env):
     False
     """
     # BEGIN PROBLEM 12
-    "*** YOUR CODE HERE ***"
+    if expressions == nil:
+        return True
+    first_val = scheme_eval(expressions.first, env)
+    if len(expressions) == 1:
+        return first_val
+    if is_scheme_false(first_val):
+        return first_val
+    return do_and_form(expressions.rest, env)
     # END PROBLEM 12
 
 def do_or_form(expressions, env):
@@ -133,7 +151,14 @@ def do_or_form(expressions, env):
     6
     """
     # BEGIN PROBLEM 12
-    "*** YOUR CODE HERE ***"
+    if expressions == nil:
+        return False
+    first_val = scheme_eval(expressions.first, env)
+    if len(expressions) == 1:
+        return first_val
+    if is_scheme_true(first_val):
+        return first_val
+    return do_or_form(expressions.rest, env)
     # END PROBLEM 12
 
 def do_cond_form(expressions, env):
@@ -153,7 +178,9 @@ def do_cond_form(expressions, env):
             test = scheme_eval(clause.first, env)
         if is_scheme_true(test):
             # BEGIN PROBLEM 13
-            "*** YOUR CODE HERE ***"
+            if clause.rest == nil:
+                return test
+            return eval_all(clause.rest, env)
             # END PROBLEM 13
         expressions = expressions.rest
 
@@ -177,7 +204,13 @@ def make_let_frame(bindings, env):
         raise SchemeError('bad bindings list in let form')
     names = vals = nil
     # BEGIN PROBLEM 14
-    "*** YOUR CODE HERE ***"
+    bindings = pair_to_list(bindings)
+    map_(bindings, lambda kv: validate_form(kv, 2, 2))
+    names = map_(bindings, lambda kv: kv.first)
+    names = list_to_pair(names)
+    validate_formals(names)
+    vals = map_(bindings, lambda kv: scheme_eval(second(kv), env))
+    vals = list_to_pair(vals)
     # END PROBLEM 14
     return env.make_child_frame(names, vals)
 
@@ -219,7 +252,9 @@ def do_mu_form(expressions, env):
     formals = expressions.first
     validate_formals(formals)
     # BEGIN PROBLEM 11
-    "*** YOUR CODE HERE ***"
+    body = expressions.rest
+    mu = MuProcedure(formals, body)
+    return mu
     # END PROBLEM 11
 
 

tests/04.py

@@ -5,7 +5,7 @@
     {
       'cases': [
         {
-          'answer': 'e92e90f58a272e7a74651635251ade14',
+          'answer': 'Pair(A, Pair(B, nil)), where: A is the symbol being bound, B is an expression whose value should be evaluated and bound to A',
           'choices': [
             r"""
             Pair(A, Pair(B, nil)), where:
@@ -34,20 +34,20 @@
             """
           ],
           'hidden': False,
-          'locked': True,
+          'locked': False,
           'multiline': False,
           'question': 'What is the structure of the expressions argument to do_define_form?'
         },
         {
-          'answer': '0ed53dce7bacc4766422abc478c5c895',
+          'answer': 'define',
           'choices': [
             'make_child_frame',
             'define',
             'lookup',
             'bindings'
           ],
           'hidden': False,
-          'locked': True,
+          'locked': False,
           'multiline': False,
           'question': r"""
           What method of a Frame instance will bind
@@ -63,20 +63,16 @@
         {
           'code': r"""
           scm> (define size 2)
-          cc3c061fb8167d02a4ddda1f1c19966e
-          # locked
+          size
           scm> size
-          2b7cdec3904f986982cbd24a0bc12887
-          # locked
+          2
           scm> (define x (+ 7 3))
-          38ba916dc1f41eb239567ee41a251ecd
-          # locked
+          x
           scm> x
-          4bc2fb48972a5d1ec1201b01e766a044
-          # locked
+          10
           """,
           'hidden': False,
-          'locked': True,
+          'locked': False,
           'multiline': False
         },
         {

tests/05.py

@@ -5,7 +5,7 @@
     {
       'cases': [
         {
-          'answer': 'fd4dd892ccea3adcf9446dc4a9738d47',
+          'answer': 'Pair(A, nil), where: A is the quoted expression',
           'choices': [
             r"""
             Pair('quote', Pair(A, nil)), where:
@@ -25,7 +25,7 @@
             """
           ],
           'hidden': False,
-          'locked': True,
+          'locked': False,
           'multiline': False,
           'question': 'What is the structure of the expressions argument to do_quote_form?'
         }
@@ -38,18 +38,15 @@
         {
           'code': r"""
           >>> do_quote_form(Pair(3, nil), global_frame)
-          3c7e8a3a2176a696c3a66418f78dff6b
-          # locked
+          3
           >>> do_quote_form(Pair('hi', nil), global_frame)
-          95448591e64e04a7a7885d5fb9b45583
-          # locked
+          'hi'
           >>> expr = Pair(Pair('+', Pair('x', Pair(2, nil))), nil)
           >>> do_quote_form(expr, global_frame) # Make sure to use Pair notation
-          2301ee746b57783004f00f39498fdaed
-          # locked
+          Pair('+', Pair('x', Pair(2, nil)))
           """,
           'hidden': False,
-          'locked': True,
+          'locked': False,
           'multiline': False
         }
       ],

tests/06.py

@@ -7,21 +7,13 @@
         {
           'code': r"""
           >>> eval_all(Pair(2, nil), env)
-          2b7cdec3904f986982cbd24a0bc12887
-          # locked
-          # choice: 2
-          # choice: SchemeError
+          2
           >>> eval_all(Pair(4, Pair(5, nil)), env)
-          b33c0f7206201b4aaeae595493888600
-          # locked
-          # choice: 4
-          # choice: 5
-          # choice: (4 5)
-          # choice: SchemeError
+          5
           >>> eval_all(nil, env) # return None (meaning undefined)
           """,
           'hidden': False,
-          'locked': True,
+          'locked': False,
           'multiline': False
         },
         {
@@ -50,40 +42,29 @@
         {
           'code': r"""
           scm> (begin (+ 2 3) (+ 5 6))
-          20169e9f217f8370ba4f37a3cf0cc2b3
-          # locked
+          11
           scm> (begin (define x 3) x)
-          3c7e8a3a2176a696c3a66418f78dff6b
-          # locked
+          3
           """,
           'hidden': False,
-          'locked': True,
+          'locked': False,
           'multiline': False
         },
         {
           'code': r"""
           scm> (begin 30 '(+ 2 2))
-          85d97cf58c044cc51a6a7d4315b4ad71
-          # locked
-          # choice: (+ 2 2)
-          # choice: '(+ 2 2)
-          # choice: 4
-          # choice: 30
+          (+ 2 2)
           scm> (define x 0)
-          38ba916dc1f41eb239567ee41a251ecd
-          # locked
+          x
           scm> (begin (define x (+ x 1)) 42 (define y (+ x 1)))
-          1a9a3321b8b99a0f9291d89be986e74c
-          # locked
+          y
           scm> x
-          eb892a26497f936d1f6cae54aacc5f51
-          # locked
+          1
           scm> y
-          2b7cdec3904f986982cbd24a0bc12887
-          # locked
+          2
           """,
           'hidden': False,
-          'locked': True,
+          'locked': False,
           'multiline': False
         },
         {

tests/07.py

@@ -7,14 +7,12 @@
         {
           'code': r"""
           scm> (lambda (x y) (+ x y)) ;; An lambda procedure is displayed exactly as it is written
-          1456de84c3edf333b6f7aee0c0624b20
-          # locked
+          (lambda (x y) (+ x y))
           scm> (lambda (x)) ; type SchemeError if you think this causes an error
-          ec908af60f03727428c7ee3f22ec3cd8
-          # locked
+          SchemeError
           """,
           'hidden': False,
-          'locked': True,
+          'locked': False,
           'multiline': False
         },
         {
@@ -49,21 +47,12 @@
           >>> lambda_line = read_line("(lambda (a b c) (+ a b c))")
           >>> lambda_proc = do_lambda_form(lambda_line.rest, env)
           >>> lambda_proc.formals # use single quotes ' around strings in your answer
-          d106bb7be6b014a9d16d74410be4a8a5
-          # locked
-          # choice: Pair('a', Pair('b', Pair('c', nil)))
-          # choice: Pair('+', Pair('a', Pair('b', Pair('c', nil))))
-          # choice: Pair(Pair('a', Pair('b', Pair('c', nil))))
+          Pair('a', Pair('b', Pair('c', nil)))
           >>> lambda_proc.body # the body is a *Scheme list* of expressions! Make sure your answer is a properly nested Pair.
-          0ef147cfe5caf670e985d95d923f4b06
-          # locked
-          # choice: Pair(Pair('+', Pair('a', Pair('b', Pair('c', nil)))), nil)
-          # choice: Pair('+', Pair('a', Pair('b', Pair('c', nil))))
-          # choice: Pair('+', 'a', 'b', 'c')
-          # choice: Pair('a', Pair('b', Pair('c')))
+          Pair(Pair('+', Pair('a', Pair('b', Pair('c', nil)))), nil)
           """,
           'hidden': False,
-          'locked': True,
+          'locked': False,
           'multiline': False
         },
         {