Add `tabseq` macro.

CHANGELOG.md

@@ -2,6 +2,8 @@
 All notable changes to this project will be documented in this file.
 
 ## 1.23.1 - ???
+- Improve default error message from `assert`.
+- Add the `tabseq` macro for simpler table comprehensions.
 - Allow setting `(dyn :task-id)` in fibers to improve context in supervisor messages. Prior to
   this change, supverisor messages over threaded channels would be from ambiguous threads/fibers.
 

src/boot/boot.janet

@@ -158,7 +158,7 @@
      (def ,v ,x)
      (if ,v
        ,v
-       (,error ,(if err err "assert failure")))))
+       (,error ,(if err err (string/format "assert failure in %j" x))))))
 
 (defn errorf
   "A combination of `error` and `string/format`. Equivalent to `(error (string/format fmt ;args))`."
@@ -606,13 +606,20 @@
   See `loop` for details.``
   [head & body]
   (def $accum (gensym))
-  ~(do (def ,$accum @[]) (loop ,head (array/push ,$accum (do ,;body))) ,$accum))
+  ~(do (def ,$accum @[]) (loop ,head (,array/push ,$accum (do ,;body))) ,$accum))
+
+(defmacro tabseq
+  ``Similar to `loop`, but accumulates key value pairs into a table.
+  See `loop` for details.``
+  [head key-body & value-body]
+  (def $accum (gensym))
+  ~(do (def ,$accum @{}) (loop ,head (,put ,$accum ,key-body (do ,;value-body))) ,$accum))
 
 (defmacro generate
   ``Create a generator expression using the `loop` syntax. Returns a fiber
   that yields all values inside the loop in order. See `loop` for details.``
   [head & body]
-  ~(fiber/new (fn [] (loop ,head (yield (do ,;body)))) :yi))
+  ~(,fiber/new (fn [] (loop ,head (yield (do ,;body)))) :yi))
 
 (defmacro coro
   "A wrapper for making fibers that may yield multiple values (coroutine). Same as `(fiber/new (fn [] ;body) :yi)`."
@@ -2768,13 +2775,13 @@
     (def c ((:where p) 0))
     (def prpt (string "debug[" level "]:" c ":" status "> "))
     (getline prpt buf nextenv))
-  (print "entering debug[" level "] - (quit) to exit")
+  (eprint "entering debug[" level "] - (quit) to exit")
   (flush)
   (run-context
     {:chunks debugger-chunks
      :on-status (debugger-on-status-var nextenv (+ 1 level) true)
      :env nextenv})
-  (print "exiting debug[" level "]")
+  (eprint "exiting debug[" level "]")
   (flush)
   (nextenv :resume-value))
 

src/core/pp.c

@@ -762,8 +762,7 @@ static const char *scanformat(
     memset(precision, '\0', 3);
     while (*p != '\0' && strchr(FMT_FLAGS, *p) != NULL)
         p++; /* skip flags */
-    if ((size_t)(p - strfrmt) >= sizeof(FMT_FLAGS) / sizeof(char))
-        janet_panic("invalid format (repeated flags)");
+    if ((size_t)(p - strfrmt) >= sizeof(FMT_FLAGS)) janet_panic("invalid format (repeated flags)");
     if (isdigit((int)(*p)))
         width[0] = *p++; /* skip width */
     if (isdigit((int)(*p)))

src/core/string.c

@@ -530,7 +530,7 @@ JANET_CORE_FN(cfun_string_join,
 
 JANET_CORE_FN(cfun_string_format,
               "(string/format format & values)",
-              "Similar to `snprintf`, but specialized for operating with Janet values. Returns "
+              "Similar to C's `snprintf`, but specialized for operating with Janet values. Returns "
               "a new string.") {
     janet_arity(argc, 1, -1);
     JanetBuffer *buffer = janet_buffer(0);