🐐 String indexing and slicing

centvrion/ast_nodes.py

@@ -833,6 +833,17 @@ class ArrayIndex(Node):
       if k not in d:
         raise CentvrionError(f"Key not found in dict")
       return vtable, d[k]
+    if isinstance(array, ValStr):
+      if isinstance(index, ValInt):
+        i = index.value()
+      elif isinstance(index, ValFrac) and index.value().denominator == 1:
+        i = index.value().numerator
+      else:
+        raise CentvrionError("String index must be a number")
+      s = array.value()
+      if i < 1 or i > len(s):
+        raise CentvrionError(f"Index {i} out of range for string of length {len(s)}")
+      return vtable, ValStr(s[i - 1])
     if not isinstance(array, ValList):
       raise CentvrionError("Cannot index a non-array value")
     if isinstance(index, ValInt):
@@ -877,6 +888,16 @@ class ArraySlice(Node):
     vtable, array = self.array.eval(vtable)
     vtable, from_val = self.from_index.eval(vtable)
     vtable, to_val = self.to_index.eval(vtable)
+    if isinstance(array, ValStr):
+      from_int = _to_index_int(from_val)
+      to_int = _to_index_int(to_val)
+      s = array.value()
+      if from_int < 1 or to_int > len(s) or from_int > to_int:
+        raise CentvrionError(
+          f"Slice [{from_int} VSQVE {to_int}] out of range"
+          f" for string of length {len(s)}"
+        )
+      return vtable, ValStr(s[from_int - 1 : to_int])
     if not isinstance(array, ValList):
       raise CentvrionError("Cannot slice a non-array value")
     from_int = _to_index_int(from_val)

centvrion/compiler/runtime/cent_runtime.c

@@ -721,6 +721,22 @@ void cent_list_push(CentValue *lst, CentValue v) {
 CentValue cent_list_index(CentValue lst, CentValue idx) {
   if (lst.type == CENT_DICT)
     return cent_dict_get(lst, idx);
+  if (lst.type == CENT_STR) {
+    long i;
+    if (idx.type == CENT_INT)
+      i = idx.ival;
+    else if (idx.type == CENT_FRAC && idx.fval.den == 1)
+      i = idx.fval.num;
+    else
+      cent_type_error("string index must be an integer");
+    long slen = (long)strlen(lst.sval);
+    if (i < 1 || i > slen)
+      cent_runtime_error("string index out of range");
+    char *ch = cent_arena_alloc(cent_arena, 2);
+    ch[0] = lst.sval[i - 1];
+    ch[1] = '\0';
+    return cent_str(ch);
+  }
   if (lst.type != CENT_LIST)
     cent_type_error("index requires a list or dict");
   long i;
@@ -736,6 +752,20 @@ CentValue cent_list_index(CentValue lst, CentValue idx) {
 }
 
 CentValue cent_list_slice(CentValue lst, CentValue lo, CentValue hi) {
+  if (lst.type == CENT_STR) {
+    if (lo.type != CENT_INT || hi.type != CENT_INT)
+      cent_type_error("slice indices must be integers");
+    long from = lo.ival;
+    long to = hi.ival;
+    long slen = (long)strlen(lst.sval);
+    if (from < 1 || to > slen || from > to)
+      cent_runtime_error("string slice out of range");
+    int len = (int)(to - from + 1);
+    char *buf = cent_arena_alloc(cent_arena, len + 1);
+    memcpy(buf, lst.sval + from - 1, len);
+    buf[len] = '\0';
+    return cent_str(buf);
+  }
   if (lst.type != CENT_LIST)
     cent_type_error("slice requires a list");
   if (lo.type != CENT_INT || hi.type != CENT_INT)