# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1480618111 -3600
# Node ID 436d7832ca668981de36b898881695cd8d4d5c30
# Parent  afa2a255d1e58ef3aa5f95806af77b759fe4148d
Introduced the itemaccess class as the base of sequence types and strings.
Added support for obtaining substrings from strings.
Added tests of string operations.
Removed the superfluous _tuple function from the sequence module.

diff -r afa2a255d1e5 -r 436d7832ca66 lib/__builtins__/sequence.py
--- a/lib/__builtins__/sequence.py	Thu Dec 01 19:09:28 2016 +0100
+++ b/lib/__builtins__/sequence.py	Thu Dec 01 19:48:31 2016 +0100
@@ -21,9 +21,9 @@
 
 from native import _isinstance
 
-class sequence:
+class itemaccess:
 
-    "A common base class for sequence types."
+    "An abstract class providing item access."
 
     def _check_index(self, index):
 
@@ -35,56 +35,6 @@
         if index < 0 or index >= len(self):
             raise IndexError(index)
 
-    def _str(self, opening, closing):
-
-        "Serialise this object with the given 'opening' and 'closing' strings."
-
-        b = buffer()
-        i = 0
-        l = self.__len__()
-        first = True
-
-        b.append(opening)
-        while i < l:
-            if first:
-                first = False
-            else:
-                b.append(", ")
-            b.append(repr(self.__get_single_item__(i)))
-            i += 1
-        b.append(closing)
-
-        return str(b)
-
-    def __contains__(self, value):
-
-        "Return whether the list contains 'value'."
-
-        # Perform a linear search of the sequence contents.
-
-        for v in self:
-
-            # Return True if the current value is equal to the specified one.
-            # Note that this is not an identity test, but an equality test.
-
-            if v == value:
-                return True
-
-        return False
-
-    def index(self, value):
-
-        "Return the index of 'value' or raise ValueError."
-
-        i = 0
-        l = len(self)
-        while i < l:
-            if self[i] == value:
-                return i
-            i += 1
-
-        raise ValueError(value)
-
     def __getitem__(self, index):
 
         "Return the item or slice specified by 'index'."
@@ -157,6 +107,60 @@
 
         return result
 
+class sequence(itemaccess):
+
+    "A common base class for sequence types."
+
+    def _str(self, opening, closing):
+
+        "Serialise this object with the given 'opening' and 'closing' strings."
+
+        b = buffer()
+        i = 0
+        l = self.__len__()
+        first = True
+
+        b.append(opening)
+        while i < l:
+            if first:
+                first = False
+            else:
+                b.append(", ")
+            b.append(repr(self.__get_single_item__(i)))
+            i += 1
+        b.append(closing)
+
+        return str(b)
+
+    def __contains__(self, value):
+
+        "Return whether the list contains 'value'."
+
+        # Perform a linear search of the sequence contents.
+
+        for v in self:
+
+            # Return True if the current value is equal to the specified one.
+            # Note that this is not an identity test, but an equality test.
+
+            if v == value:
+                return True
+
+        return False
+
+    def index(self, value):
+
+        "Return the index of 'value' or raise ValueError."
+
+        i = 0
+        l = len(self)
+        while i < l:
+            if self[i] == value:
+                return i
+            i += 1
+
+        raise ValueError(value)
+
     def __eq__(self, other):
 
         "Return whether this sequence is equal to 'other'."
@@ -211,6 +215,4 @@
     else:
         return y
 
-def _tuple(l): pass
-
 # vim: tabstop=4 expandtab shiftwidth=4
diff -r afa2a255d1e5 -r 436d7832ca66 lib/__builtins__/str.py
--- a/lib/__builtins__/str.py	Thu Dec 01 19:09:28 2016 +0100
+++ b/lib/__builtins__/str.py	Thu Dec 01 19:48:31 2016 +0100
@@ -20,9 +20,10 @@
 """
 
 from __builtins__.operator import _binary_op, _negate
+from __builtins__.sequence import itemaccess
 import native
 
-class basestring:
+class basestring(itemaccess):
 
     "The base class for all strings."
 
@@ -121,6 +122,15 @@
     def strip(self, chars=None): pass
     def upper(self): pass
 
+    # Special implementation methods.
+
+    def __get_single_item__(self, index):
+
+        "Return the item at the normalised (positive) 'index'."
+
+        self._check_index(index)
+        return native._str_substr(self, index, 1)
+
 class string(basestring):
     pass
 
diff -r afa2a255d1e5 -r 436d7832ca66 lib/native.py
--- a/lib/native.py	Thu Dec 01 19:09:28 2016 +0100
+++ b/lib/native.py	Thu Dec 01 19:48:31 2016 +0100
@@ -60,6 +60,7 @@
 def _str_eq(self, other): pass
 def _str_len(self): pass
 def _str_nonempty(self): pass
+def _str_substr(self, start, size): pass
 
 # List operations.
 
diff -r afa2a255d1e5 -r 436d7832ca66 templates/native.c
--- a/templates/native.c	Thu Dec 01 19:09:28 2016 +0100
+++ b/templates/native.c	Thu Dec 01 19:48:31 2016 +0100
@@ -302,7 +302,7 @@
     char *r = (char *) __ALLOCATE(n, sizeof(char));
 
     strncpy(r, s, n);
-    strncpy(r + strlen(s), o, n - strlen(s));
+    strncpy(r + strlen(s), o, n - strlen(s)); /* should null terminate */
 
     /* Return a new string. */
     return __new_str(r);
@@ -363,6 +363,24 @@
     return strlen(s) ? __builtins___boolean_True : __builtins___boolean_False;
 }
 
+__attr __fn_native__str_substr(__attr __args[])
+{
+    __attr * const self = &__args[1];
+    __attr * const start = &__args[2];
+    __attr * const size = &__args[3];
+    /* self.__data__ interpreted as string */
+    char *s = __load_via_object(self->value, __pos___data__).strvalue, *sub;
+    /* start.__data__ interpreted as int */
+    int i = __load_via_object(start->value, __pos___data__).intvalue;
+    /* size.__data__ interpreted as int */
+    int l = __load_via_object(size->value, __pos___data__).intvalue;
+
+    /* Reserve space for a new string. */
+    sub = (char *) __ALLOCATE(l + 1, sizeof(char));
+    strncpy(sub, s + i, l); /* does not null terminate but final byte should be zero */
+    return __new_str(sub);
+}
+
 __attr __fn_native__list_init(__attr __args[])
 {
     __attr * const size = &__args[1];
@@ -649,7 +667,7 @@
     {
         o = __load_via_object(data->attrs[i].value, __pos___data__).strvalue;
         n = strlen(o);
-        strncpy(s + j, o, n);
+        strncpy(s + j, o, n); /* does not null terminate but final byte should be zero */
         j += n;
     }
 
diff -r afa2a255d1e5 -r 436d7832ca66 templates/native.h
--- a/templates/native.h	Thu Dec 01 19:09:28 2016 +0100
+++ b/templates/native.h	Thu Dec 01 19:48:31 2016 +0100
@@ -40,6 +40,7 @@
 __attr __fn_native__str_eq(__attr __args[]);
 __attr __fn_native__str_len(__attr __args[]);
 __attr __fn_native__str_nonempty(__attr __args[]);
+__attr __fn_native__str_substr(__attr __args[]);
 
 __attr __fn_native__list_init(__attr __args[]);
 __attr __fn_native__list_setsize(__attr __args[]);
diff -r afa2a255d1e5 -r 436d7832ca66 tests/string.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/string.py	Thu Dec 01 19:48:31 2016 +0100
@@ -0,0 +1,15 @@
+s = "Hello"
+s += " world!"
+print s                     # Hello world!
+
+s2 = "Hello worlds!"
+print s2                    # Hello worlds!
+print s < s2                # True
+print s <= s2               # True
+print s == s2               # False
+print s != s2               # True
+print s >= s2               # False
+print s > s2                # False
+
+print s[0]                  # H
+print s[-1]                 # !