erlang: list comprehensions (+12 tests)

lib/erlang/parser-expr.sx

@@ -281,12 +281,56 @@
   (fn
     (st)
     (er-expect! st "punct" "[")
-    (if
+    (cond
       (er-is? st "punct" "]")
       (do (er-advance! st) {:type "nil"})
-      (let
-        ((elems (list (er-parse-expr-prec st 0))))
-        (er-parse-list-tail st elems)))))
+      :else (let
+        ((first (er-parse-expr-prec st 0)))
+        (cond
+          (er-is? st "punct" "||") (er-parse-list-comp st first)
+          :else (er-parse-list-tail st (list first)))))))
+
+(define
+  er-parse-list-comp
+  (fn
+    (st head)
+    (er-advance! st)
+    (let
+      ((quals (list (er-parse-lc-qualifier st))))
+      (er-parse-list-comp-tail st head quals))))
+
+(define
+  er-parse-list-comp-tail
+  (fn
+    (st head quals)
+    (cond
+      (er-is? st "punct" ",")
+      (do
+        (er-advance! st)
+        (append! quals (er-parse-lc-qualifier st))
+        (er-parse-list-comp-tail st head quals))
+      (er-is? st "punct" "]")
+      (do (er-advance! st) {:head head :qualifiers quals :type "lc"})
+      :else (error
+        (str
+          "Erlang parse: expected ',' or ']' in list comprehension, got '"
+          (er-cur-value st)
+          "'")))))
+
+(define
+  er-parse-lc-qualifier
+  (fn
+    (st)
+    (let
+      ((e (er-parse-expr-prec st 0)))
+      (cond
+        (er-is? st "punct" "<-")
+        (do
+          (er-advance! st)
+          (let
+            ((source (er-parse-expr-prec st 0)))
+            {:kind "gen" :pattern e :source source}))
+        :else {:kind "filter" :expr e}))))
 
 (define
   er-parse-list-tail