Merge pull request #1095 from ml-2/ml

Add `keep-syntax` and `keep-syntax!` functions

src/boot/boot.janet

@@ -1232,6 +1232,29 @@
      (,eprintf (,dyn :pretty-format "%q") ,s)
      ,s))
 
+(defn keep-syntax
+  ``Creates a tuple with the tuple type and sourcemap of `before` but the
+  elements of `after`. If either one of its argements is not a tuple, returns
+  `after` unmodified. Useful to preserve syntactic information when transforming
+  an ast in macros.``
+  [before after]
+  (if (and (= :tuple (type before))
+           (= :tuple (type after)))
+    (do
+      (def res (if (= :parens (tuple/type before))
+                 (tuple/slice after)
+                 (tuple/brackets ;after)))
+      (tuple/setmap res ;(tuple/sourcemap before)))
+    after))
+
+(defn keep-syntax!
+  ``Like `keep-syntax`, but if `after` is an array, it is coerced into a tuple.
+  Useful to preserve syntactic information when transforming an ast in macros.``
+  [before after]
+  (keep-syntax before (if (= :array (type after))
+                        (tuple/slice after)
+                        after)))
+
 (defmacro ->
   ``Threading macro. Inserts x as the second value in the first form
   in `forms`, and inserts the modified first form into the second form
@@ -1242,7 +1265,7 @@
                  (tuple (in n 0) (array/slice n 1))
                  (tuple n @[])))
     (def parts (array/concat @[h last] t))
-    (tuple/slice parts 0))
+    (keep-syntax! n parts))
   (reduce fop x forms))
 
 (defmacro ->>
@@ -1255,7 +1278,7 @@
                  (tuple (in n 0) (array/slice n 1))
                  (tuple n @[])))
     (def parts (array/concat @[h] t @[last]))
-    (tuple/slice parts 0))
+    (keep-syntax! n parts))
   (reduce fop x forms))
 
 (defmacro -?>
@@ -1271,7 +1294,7 @@
                  (tuple n @[])))
     (def sym (gensym))
     (def parts (array/concat @[h sym] t))
-    ~(let [,sym ,last] (if ,sym ,(tuple/slice parts 0))))
+    ~(let [,sym ,last] (if ,sym ,(keep-syntax! n parts))))
   (reduce fop x forms))
 
 (defmacro -?>>
@@ -1287,7 +1310,7 @@
                  (tuple n @[])))
     (def sym (gensym))
     (def parts (array/concat @[h] t @[sym]))
-    ~(let [,sym ,last] (if ,sym ,(tuple/slice parts 0))))
+    ~(let [,sym ,last] (if ,sym ,(keep-syntax! n parts))))
   (reduce fop x forms))
 
 (defn- walk-ind [f form]
@@ -1311,10 +1334,7 @@
     :table (walk-dict f form)
     :struct (table/to-struct (walk-dict f form))
     :array (walk-ind f form)
-    :tuple (let [x (walk-ind f form)]
+    :tuple (keep-syntax! form (walk-ind f form))
-             (if (= :parens (tuple/type form))
-               (tuple/slice x)
-               (tuple/brackets ;x)))
     form))
 
 (defn postwalk

test/suite0010.janet

@@ -44,6 +44,43 @@
 (assert (= :brackets (tuple/type (1 (macex1 '~[1 2 3 4])))) "macex1 qq bracket tuple")
 (assert (deep= (macex1 '~@[1 2 3 4 ,blah]) '~@[1 2 3 4 ,blah]) "macex1 qq array")
 
+# Sourcemaps in threading macros
+(defn check-threading [macro expansion]
+  (def expanded (macex1 (tuple macro 0 '(x) '(y))))
+  (assert (= expanded expansion) (string macro " expansion value"))
+  (def smap-x (tuple/sourcemap (get expanded 1)))
+  (def smap-y (tuple/sourcemap expanded))
+  (def line first)
+  (defn column [t] (t 1))
+  (assert (not= smap-x [-1 -1]) (string macro " x sourcemap existence"))
+  (assert (not= smap-y [-1 -1]) (string macro " y sourcemap existence"))
+  (assert (or (< (line smap-x) (line smap-y))
+              (and (= (line smap-x) (line smap-y))
+                   (< (column smap-x) (column smap-y))))
+          (string macro " relation between x and y sourcemap")))
+
+(check-threading '-> '(y (x 0)))
+(check-threading '->> '(y (x 0)))
+
+# keep-syntax
+(let [brak '[1 2 3]
+      par '(1 2 3)]
+
+  (tuple/setmap brak 2 1)
+
+  (assert (deep= (keep-syntax brak @[1 2 3]) @[1 2 3]) "keep-syntax brackets ignore array")
+  (assert (= (keep-syntax! brak @[1 2 3]) '[1 2 3]) "keep-syntax! brackets replace array")
+
+  (assert (= (keep-syntax! par (map inc @[1 2 3])) '(2 3 4)) "keep-syntax! parens coerce array")
+  (assert (not= (keep-syntax! brak @[1 2 3]) '(1 2 3)) "keep-syntax! brackets not parens")
+  (assert (not= (keep-syntax! par @[1 2 3]) '[1 2 3]) "keep-syntax! parens not brackets")
+  (assert (= (tuple/sourcemap brak)
+             (tuple/sourcemap (keep-syntax! brak @[1 2 3]))) "keep-syntax! brackets source map")
+
+  (keep-syntax par brak)
+  (assert (not= (tuple/sourcemap brak) (tuple/sourcemap par)) "keep-syntax no mutate")
+  (assert (= (keep-syntax 1 brak) brak) "keep-syntax brackets ignore type"))
+
 # Cancel test
 (def f (fiber/new (fn [&] (yield 1) (yield 2) (yield 3) 4) :yti))
 (assert (= 1 (resume f)) "cancel resume 1")