lib/load-file-once: basic support for multiple imports

lib/README.md

@@ -17,13 +17,19 @@ However, here are some guidelines.
   is not possible, for example for macros, give them a name starting
   with an underscore.
 
-- Support successive imports safely by giving the same definitions
-  again.
-
 If a module provides tests, you may run against an implementation IMPL
 with these commands.
 ```
 make IMPL^stepA
 cd tests
 python ../runtest.py lib/MODULE.mal ../IMPL/run
 ```
+
+Users and implementors should use the following syntax in order to
+ensure that the same file is only loaded once.
+
+```
+(load-file      "../lib/load-file-once.mal")
+(load-file-once "../lib/foo.mal")
+(load-file-once "../lib/bar.mal")
+```

lib/load-file-once.mal

@@ -0,0 +1,18 @@
+;; Like load-file, but will never load the same path twice.
+
+;; This file is normally loaded with `load-file`, so it needs a
+;; different mechanism to neutralize multiple inclusions of
+;; itself. Moreover, the file list should never be reset.
+
+(def! load-file-once
+  (try*
+    load-file-once
+  (catch* _
+    (let* [seen (atom {"../lib/load-file-once.mal" nil})]
+      (fn* [filename]
+        (if (not (contains? @seen filename))
+          (do
+            (swap! seen assoc filename nil)
+            (load-file filename))))))))
+
+nil

lib/perf.mal

@@ -1,6 +1,7 @@
 ;; Mesure performances.
 
-(load-file "../lib/trivial.mal")        ; gensym inc
+(load-file      "../lib/load-file-once.mal")
+(load-file-once "../lib/trivial.mal")   ; gensym inc
 
 ;; Evaluate an expression, but report the time spent
 (defmacro! time

lib/test_cascade.mal

@@ -1,6 +1,7 @@
 ;; Iteration on evaluations interpreted as boolean values.
 
-(load-file "../lib/trivial.mal")        ; gensym
+(load-file      "../lib/load-file-once.mal")
+(load-file-once "../lib/trivial.mal")   ; gensym
 
 ;; `(cond test1 result1 test2 result2 .. testn resultn)`
 ;; is rewritten (in the step files) as

lib/threading.mal

@@ -1,6 +1,7 @@
 ;; Composition of partially applied functions.
 
-(load-file "../lib/reducers.mal")       ; reduce
+(load-file      "../lib/load-file-once.mal")
+(load-file-once "../lib/reducers.mal")  ; reduce
 
 ;; Rewrite x (a a1 a2) .. (b b1 b2) as
 ;;   (b (.. (a x a1 a2) ..) b1 b2)

tests/lib/load-file-once-inc.mal

@@ -0,0 +1 @@
+(swap! counter (fn* [x] (+ 1 x)))

tests/lib/load-file-once.mal

@@ -0,0 +1,38 @@
+(def! counter (atom 0))
+;=>(atom 0)
+
+;; The counter is increased by each `load-file`.
+(load-file      "../tests/lib/load-file-once-inc.mal")
+;=>1
+(load-file      "../tests/lib/load-file-once-inc.mal")
+;=>2
+
+;; load-file-once is available
+(load-file      "../lib/load-file-once.mal")
+;=>nil
+
+;; First import actually calls `load-file`.
+(load-file-once "../tests/lib/load-file-once-inc.mal")
+;=>3
+
+;; Later imports do nothing.
+(load-file-once "../tests/lib/load-file-once-inc.mal")
+;=>nil
+@counter
+;=>3
+
+;; Loading the module twice does not reset its memory.
+(load-file      "../lib/load-file-once.mal")
+;=>nil
+(load-file-once "../tests/lib/load-file-once-inc.mal")
+;=>nil
+@counter
+;=>3
+
+;; even if done with itself
+(load-file-once "../lib/load-file-once.mal")
+;=>nil
+(load-file-once "../tests/lib/load-file-once-inc.mal")
+;=>nil
+@counter
+;=>3

tests/lib/memoize.mal

@@ -1,6 +1,6 @@
-(load-file "../tests/computations.mal")
-;=>nil
-(load-file "../lib/memoize.mal")
+(load-file      "../lib/load-file-once.mal")
+(load-file-once "../tests/computations.mal")
+(load-file-once "../lib/memoize.mal")
 ;=>nil
 
 (def! N 32)

tests/lib/pprint.mal

@@ -1,4 +1,5 @@
-(load-file "../lib/pprint.mal")
+(load-file      "../lib/load-file-once.mal")
+(load-file-once "../lib/pprint.mal")
 ;=>nil
 
 (pprint '(7 8 9 "ten" [11 12 [13 14]] 15 16))

tests/lib/protocols.mal

@@ -1,4 +1,5 @@
-(load-file "../lib/protocols.mal")
+(load-file      "../lib/load-file-once.mal")
+(load-file-once "../lib/protocols.mal")
 ;=>nil
 
 ;; Testing find-type for normal objects.

tests/lib/reducers.mal

@@ -1,4 +1,5 @@
-(load-file "../lib/reducers.mal")
+(load-file      "../lib/load-file-once.mal")
+(load-file-once "../lib/reducers.mal")
 ;=>nil
 
 ;; Testing reduce

tests/lib/test_cascade.mal

@@ -1,4 +1,5 @@
-(load-file "../lib/test_cascade.mal")
+(load-file      "../lib/load-file-once.mal")
+(load-file-once "../lib/test_cascade.mal")
 ;=>nil
 
 ;; Testing or

tests/lib/threading.mal

@@ -1,4 +1,5 @@
-(load-file "../lib/threading.mal")
+(load-file "../lib/load-file-once.mal")
+(load-file-once "../lib/threading.mal")
 ;=>nil
 
 ;; Testing -> macro

tests/lib/trivial.mal

@@ -1,4 +1,5 @@
-(load-file "../lib/trivial.mal")
+(load-file      "../lib/load-file-once.mal")
+(load-file-once "../lib/trivial.mal")
 ;=>nil
 
 (inc 12)

tests/perf1.mal

@@ -1,6 +1,7 @@
-(load-file "../lib/threading.mal")      ; ->
-(load-file "../lib/perf.mal")           ; time
-(load-file "../lib/test_cascade.mal")   ; or
+(load-file      "../lib/load-file-once.mal")
+(load-file-once "../lib/threading.mal")    ; ->
+(load-file-once "../lib/perf.mal")         ; time
+(load-file-once "../lib/test_cascade.mal") ; or
 
 ;;(prn "Start: basic macros performance test")
 

tests/perf2.mal

@@ -1,5 +1,6 @@
-(load-file "../tests/computations.mal")     ; fib sumdown
-(load-file "../lib/perf.mal")               ; time
+(load-file      "../lib/load-file-once.mal")
+(load-file-once "../tests/computations.mal") ; fib sumdown
+(load-file-once "../lib/perf.mal")           ; time
 
 ;;(prn "Start: basic math/recursion test")
 

tests/perf3.mal

@@ -1,6 +1,7 @@
-(load-file "../lib/threading.mal")      ; ->
-(load-file "../lib/perf.mal")           ; run-fn-for
-(load-file "../lib/test_cascade.mal")   ; or
+(load-file      "../lib/load-file-once.mal")
+(load-file-once "../lib/threading.mal")    ; ->
+(load-file-once "../lib/perf.mal")         ; run-fn-for
+(load-file-once "../lib/test_cascade.mal") ; or
 
 ;;(prn "Start: basic macros/atom test")