🐐 Array slicing

centvrion/ast_nodes.py

@@ -847,6 +847,49 @@ class ArrayIndex(Node):
     return vtable, lst[i - 1]
 
 
+def _to_index_int(val):
+  if isinstance(val, ValInt):
+    return val.value()
+  if isinstance(val, ValFrac) and val.value().denominator == 1:
+    return val.value().numerator
+  raise CentvrionError("Array index must be a number")
+
+
+class ArraySlice(Node):
+  def __init__(self, array, from_index, to_index) -> None:
+    self.array = array
+    self.from_index = from_index
+    self.to_index = to_index
+
+  def __eq__(self, other):
+    return (type(self) == type(other)
+      and self.array == other.array
+      and self.from_index == other.from_index
+      and self.to_index == other.to_index)
+
+  def __repr__(self) -> str:
+    return f"ArraySlice({self.array!r}, {self.from_index!r}, {self.to_index!r})"
+
+  def print(self):
+    return f"{self.array.print()}[{self.from_index.print()} VSQVE {self.to_index.print()}]"
+
+  def _eval(self, vtable):
+    vtable, array = self.array.eval(vtable)
+    vtable, from_val = self.from_index.eval(vtable)
+    vtable, to_val = self.to_index.eval(vtable)
+    if not isinstance(array, ValList):
+      raise CentvrionError("Cannot slice a non-array value")
+    from_int = _to_index_int(from_val)
+    to_int = _to_index_int(to_val)
+    lst = array.value()
+    if from_int < 1 or to_int > len(lst) or from_int > to_int:
+      raise CentvrionError(
+        f"Slice [{from_int} VSQVE {to_int}] out of range"
+        f" for array of length {len(lst)}"
+      )
+    return vtable, ValList(lst[from_int - 1 : to_int])
+
+
 class SiStatement(Node):
   def __init__(self, test, statements, else_part) -> None:
     self.test = test

centvrion/compiler/emit_expr.py

@@ -2,7 +2,7 @@ from centvrion.errors import CentvrionError
 from centvrion.ast_nodes import (
   String, InterpolatedString, Numeral, Fractio, Bool, Nullus, ID,
   BinOp, UnaryMinus, UnaryNot,
-  ArrayIndex, DataArray, DataRangeArray, DataDict,
+  ArrayIndex, ArraySlice, DataArray, DataRangeArray, DataDict,
   BuiltIn, Invoca, Fvnctio,
   num_to_int, frac_to_fraction,
 )
@@ -120,6 +120,15 @@ def emit_expr(node, ctx):
     tmp = ctx.fresh_tmp()
     return arr_lines + idx_lines + [f"CentValue {tmp} = cent_list_index({arr_var}, {idx_var});"], tmp
 
+  if isinstance(node, ArraySlice):
+    arr_lines, arr_var = emit_expr(node.array, ctx)
+    lo_lines, lo_var = emit_expr(node.from_index, ctx)
+    hi_lines, hi_var = emit_expr(node.to_index, ctx)
+    tmp = ctx.fresh_tmp()
+    return arr_lines + lo_lines + hi_lines + [
+      f"CentValue {tmp} = cent_list_slice({arr_var}, {lo_var}, {hi_var});"
+    ], tmp
+
   if isinstance(node, DataArray):
     lines = []
     tmp = ctx.fresh_tmp()

centvrion/compiler/runtime/cent_runtime.c

@@ -735,6 +735,22 @@ CentValue cent_list_index(CentValue lst, CentValue idx) {
   return lst.lval.items[i - 1];
 }
 
+CentValue cent_list_slice(CentValue lst, CentValue lo, CentValue hi) {
+  if (lst.type != CENT_LIST)
+    cent_type_error("slice requires a list");
+  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;
+  if (from < 1 || to > lst.lval.len || from > to)
+    cent_runtime_error("slice out of range");
+  int len = (int)(to - from + 1);
+  CentValue result = cent_list_new(len);
+  for (long j = from; j <= to; j++)
+    cent_list_push(&result, lst.lval.items[j - 1]);
+  return result;
+}
+
 void cent_list_index_set(CentValue *lst, CentValue idx, CentValue v) {
   if (lst->type == CENT_DICT) {
     cent_dict_set(lst, idx, v);

centvrion/compiler/runtime/cent_runtime.h

@@ -234,6 +234,7 @@ void      cent_adivnge(CentValue path, CentValue content);      /* ADIVNGE */
 CentValue cent_list_new(int cap);
 void      cent_list_push(CentValue *lst, CentValue v);
 CentValue cent_list_index(CentValue lst, CentValue idx);        /* 1-based */
+CentValue cent_list_slice(CentValue lst, CentValue lo, CentValue hi); /* 1-based, inclusive */
 void      cent_list_index_set(CentValue *lst, CentValue idx, CentValue v);
 
 /* ------------------------------------------------------------------ */

centvrion/parser.py

@@ -326,6 +326,10 @@ class Parser():
     def array_index(tokens):
       return ast_nodes.ArrayIndex(tokens[0], tokens[2])
 
+    @self.pg.production('expression : expression SYMBOL_LBRACKET expression KEYWORD_VSQVE expression SYMBOL_RBRACKET', precedence='INDEX')
+    def array_slice(tokens):
+      return ast_nodes.ArraySlice(tokens[0], tokens[2], tokens[4])
+
     # ids
     @self.pg.production('ids : SYMBOL_LPARENS id_list')
     def ids(tokens):