alisp: add TODO for sv_t

As stream_stop requires a valid FILE pointer (fseek), we need to do it
before we close the pipe.

alisp.org

@@ -70,7 +70,7 @@ Also ensure stream_eoc is false.
 - Seeking forward/backward on a bad stream (should stop at 0)
 - Seeking forward/backward too far (should clamp)
 - Seeking forward/backward zero sum via relative index (stream_seek)
-**** TODO Test substring
+**** DONE Test substring
 [[file:test/test_stream.c::void stream_test_substr(void)]]
 - Substr on bad stream (NULL sv)
 - Substr on bad position/size (NULL sv)
@@ -196,6 +196,12 @@ functions to construct and deconstruct strings as lisps.
 Should we capitalise symbols?  This way, we limit the symbol table's
 possible options a bit (potentially we could design a better hashing
 algorithm?) and it would be kinda like an actual Lisp.
+*** TODO sv_t
+[[file:include/alisp/sv.h::/// String Views]]
+**** TODO sv_substr
+Takes an index and a size, returns a string view to that substring.
+**** TODO sv_chop_left and sv_chop_right
+Super obvious.
 ** Completed
 *** DONE Test value constructors and destructors :test:
 Test if ~make_int~ works with ~as_int,~ ~intern~ with ~as_sym~.

src/main.c

@@ -69,9 +69,9 @@ int main(int argc, char *argv[])
 
   LOG("[INFO]: Initialised stream for `%s`\n", stream.name);
 end:
+  stream_stop(&stream);
   if (pipe)
     fclose(pipe);
-  stream_stop(&stream);
   return ret;
 }
 

src/stream.c

@@ -5,6 +5,7 @@
  * Commentary:
  */
 
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -95,8 +96,11 @@ void stream_stop(stream_t *stream)
   case STREAM_TYPE_STRING:
     free(stream->string.data);
     break;
-  case STREAM_TYPE_PIPE:
   case STREAM_TYPE_FILE:
+    // ensure we reset the FILE pointer to the start
+    fseek(stream->pipe.file, 0, SEEK_SET);
+    // fallthrough
+  case STREAM_TYPE_PIPE:
     // Must cleanup vector
     vec_free(&stream->pipe.cache);
     break;
@@ -313,11 +317,11 @@ sv_t stream_substr(stream_t *stream, u64 size)
 
   // See if I can go forward enough to make this substring
   u64 current_position = stream->position;
-  bool successful      = stream_seek_forward(stream, size);
+  u64 successful       = stream_seek_forward(stream, size);
   // Reset the position in either situation
   stream->position = current_position;
 
-  if (!successful)
+  if (successful != size)
     return SV(NULL, 0);
 
   char *ptr = NULL;

test/test_stream.c

@@ -277,7 +277,109 @@ void stream_test_seek(void)
 void stream_test_substr(void)
 {
   TEST_START();
-  TODO("Not implemented");
+  u64 size     = rand() % (ARRSIZE(words_text) - 1);
+  u64 position = ARRSIZE(words_text) - size - 1;
+
+  // Taking substrings of invalid streams
+  {
+    stream_t stream = {0};
+    stream_init_file(&stream, NULL, invalid_fp);
+
+    // Relative
+    {
+      sv_t result = stream_substr(&stream, size);
+      TEST(result.data == NULL && result.size == 0,
+           "Relative substring with size %lu on invalid stream should be NULL",
+           size);
+    }
+
+    // Absolute
+    {
+      sv_t result = stream_substr_abs(&stream, position, size);
+      TEST(result.data == NULL && result.size == 0,
+           "Absolute substring @%lu with size %lu on invalid stream should be "
+           "NULL",
+           position, size);
+    }
+
+    stream_stop(&stream);
+  }
+
+  // Taking substrings of valid streams
+  {
+    stream_t stream = {0};
+    stream_init_file(&stream, valid_filename, valid_fp);
+
+    // Absolute
+    {
+      sv_t result = stream_substr_abs(&stream, position, size);
+      TEST(result.data && result.size,
+           "Absolute substring @%lu with size %lu on valid stream should be "
+           "nonzero",
+           position, size);
+
+      TEST(result.size == size, "Substring has right size (%lu)", result.size);
+
+      sv_t expected = SV((char *)words_text + position, size);
+      TEST(strncmp(result.data, expected.data, result.size) == 0,
+           "Expect the substring to be the same as the data we put in");
+    }
+
+    // Relative
+    {
+      sv_t result = stream_substr(&stream, size);
+      TEST(result.data && result.size,
+           "Relative substring with size %lu should be nonzero", size);
+
+      TEST(result.size == size, "Substring has right size (%lu)", result.size);
+
+      sv_t expected = SV((char *)words_text, size);
+      TEST(strncmp(result.data, expected.data, result.size) == 0,
+           "Expect the substring to be the same as the data we put in");
+    }
+
+    // Relative substring after seeking
+    {
+      // Shift forward to a random position
+      assert(stream_seek_forward(&stream, position)); // not a test
+      sv_t result = stream_substr(&stream, size);
+      TEST(result.data && result.size,
+           "Relative substring with size %lu after seeking %lu bytes should be "
+           "nonzero",
+           size, position);
+
+      TEST(result.size == size, "Substring has right size (%lu)", result.size);
+
+      sv_t expected = SV((char *)words_text + position, size);
+      TEST(strncmp(result.data, expected.data, result.size) == 0,
+           "Expect the substring to be the same as the data we put in");
+
+      // Shift back to the original position.
+      assert(stream_seek_backward(&stream, position)); // not a test
+    }
+
+    // Bad substrings
+    {
+      {
+        sv_t result = stream_substr_abs(&stream, stream_size(&stream), 100);
+        TEST(!result.data && !result.size,
+             "Absolute substring at %lu of 100 bytes is invalid",
+             stream_size(&stream));
+      }
+
+      assert(stream_seek_forward(&stream, stream_size(&stream))); // not a test
+      {
+        sv_t result = stream_substr(&stream, 100);
+        TEST(!result.data && !result.size,
+             "Relative substring with size 100 after seeking %lu bytes is "
+             "invalid",
+             stream.position);
+      }
+    }
+
+    stream_stop(&stream);
+  }
+  TEST_END();
 }
 
 void stream_test_till(void)
@@ -305,6 +407,7 @@ MAKE_TEST_SUITE(STREAM_SUITE, "Stream Tests",
                 MAKE_TEST_FN(stream_test_file),
                 MAKE_TEST_FN(stream_test_peek_next),
                 MAKE_TEST_FN(stream_test_seek),
+                MAKE_TEST_FN(stream_test_substr),
                 MAKE_TEST_FN(stream_test_epilogue), );
 
 /* Copyright (C) 2026 Aryadev Chavali

test/test_vec.c

@@ -37,7 +37,7 @@ void vec_test_concat(void)
   TEST_END();
 }
 
-void vec_test_substr(void)
+void vec_test_gen_substr(void)
 {
   TEST_START();
   sys_t system = {0};
@@ -73,7 +73,8 @@ void vec_test_substr(void)
 
 MAKE_TEST_SUITE(VEC_SUITE, "Vector Tests",
 
-                MAKE_TEST_FN(vec_test_concat), MAKE_TEST_FN(vec_test_substr), );
+                MAKE_TEST_FN(vec_test_concat),
+                MAKE_TEST_FN(vec_test_gen_substr), );
 
 /* Copyright (C) 2026 Aryadev Chavali