From 1180255e7b0e9e70a6d8b7665ac8a77886ef16a5 Mon Sep 17 00:00:00 2001
From: Přemysl Janouch <p.janouch@gmail.com>
Date: Sat, 16 Apr 2016 23:44:52 +0200
Subject: calc: comment updates, import fixes

---
 plugins/zyklonb/calc | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/plugins/zyklonb/calc b/plugins/zyklonb/calc
index e2f4be9..deea424 100755
--- a/plugins/zyklonb/calc
+++ b/plugins/zyklonb/calc
@@ -93,7 +93,10 @@
 
 ; --- Calculator ---------------------------------------------------------------
 
-; Evaluator derived from the example in The Scheme Programming Language
+; Evaluator derived from the example in The Scheme Programming Language.
+;
+; Even though EVAL with a carefully crafted environment would also do a good
+; job at sandboxing, it would probably be impossible to limit execution time...
 
 (define (env-new formals actuals env)
   (cond [(null? formals) env]
@@ -108,7 +111,8 @@
     (error 'check-reductions "reduction limit exceeded")
     (set-car! r (- (car r) 1))))
 
-; TODO - think about implementing more syntactical constructs
+; TODO - think about implementing more syntactical constructs,
+;   however there's not much point in having anything else in a calculator...
 (define (exec expr r env)
   (check-reductions r)
   (cond [(symbol? expr) (env-lookup expr env)]
@@ -135,6 +139,7 @@
     [(_) '()]
     [(_ a b ...) (cons (cons (quote a) a) (forward b ...))]))
 
+; ...which can't prevent me from simply importing most of the standard library
 (define base-library
   (forward
     ; Equivalence, procedure predicate, booleans
@@ -158,12 +163,12 @@
     symbol? symbol=? symbol->string string->symbol
     ; Characters
     char? char=? char<? char>? char<=? char>=?  char->integer integer->char
-    ; Strings; XXX make-string can make an arbitrary length string -> removed
+    ; Strings; XXX - omitted make-string - can cause OOM
     string? string=? string<? string>? string<=? string>=?
-    make-string string string-length string-ref substring
+    string string-length string-ref substring
     string-append string->list list->string string-for-each string-copy
-    ; Vectors; XXX make-vector can make an arbitrary length vectors -> removed
-    vector? make-vector vector vector-length vector-ref vector-set!
+    ; Vectors; XXX - omitted make-vector - can cause OOM
+    vector? vector vector-length vector-ref vector-set!
     vector->list list->vector vector-fill! vector-map vector-for-each
     ; Control features
     apply call/cc values call-with-values dynamic-wind))
-- 
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