[MLton-commit] r4734

[Vesa Karvonen]

Elaborated.
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U   mltonlib/trunk/com/ssh/extended-basis/unstable/readme.txt

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Modified: mltonlib/trunk/com/ssh/extended-basis/unstable/readme.txt
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--- mltonlib/trunk/com/ssh/extended-basis/unstable/readme.txt	2006-10-20 01:51:30 UTC (rev 4733)
+++ mltonlib/trunk/com/ssh/extended-basis/unstable/readme.txt	2006-10-20 15:25:54 UTC (rev 4734)
@@ -1,4 +1,53 @@
-This library implements a number of minor extensions to the signatures and
-structures of the Standard ML Basis Library.  The reason for extending the
-Basis Library in this way is that the extensions are naturally associated
-with specific basis library modules.
+Extended Basis Library
+----------------------
+
+   This library implements a number of minor extensions to the signatures
+   and structures of the Standard ML Basis Library [1].  These extensions
+   are done in a non-intrusive manner by simply rebinding the signatures
+   and structures of the basis library.  The reason for extending the
+   basis library in this way is that the extensions are naturally
+   associated with specific basis library modules.  Extensions include
+   things like isomorphisms and embeddings (pairs of the form (toX,
+   fromX)), bounds (pairs of the form (minX, maxX)), and simple utility
+   functions such as isZero, isEven and isOdd.
+
+   The basis library, while certainly not perfect, is a valuable library
+   and it doesn't make sense to throw it away.  There is a book describing
+   the basis library and people just learning SML are likely to spend time
+   learning the basis library.  It makes sense to build on that knowledge.
+
+   However, maintaining 100% basis library compatibility is unlikely to
+   lead to an "optimal" design.  In particular, here is what the basis
+   library book [1] says (page 11, start of section 2, emphasis added):
+
+      "We view the signature and structure names used below as being
+      *reserved*.  For an implementation to be conforming, any module it
+      provides that is named in the SML Basis Library must *exactly* match
+      the description specified in the Library."
+
+   So, the design of the basis library is supposed to be more or less cast
+   in stone - at least if you want to claim that you've implemented the
+   SML Basis Library.  However, one can argue that the basis library
+   contains an organizational framework that goes beyond the exact
+   signatures and structures specified.  For many simple extensions there
+   is a place in that organizational framework, and while it isn't
+   technically necessary to extended the basis library, it makes sense to
+   do so because it can reduce the learning curve and make the entirety
+   easier to use.
+
+   On the other hand, it probably doesn't make sense to put everything
+   into such extended basis library.  As a rule of thumb, things that
+   naturally belong (fuzzy, yes) to specific basis library modules and
+   what those things depend on should go into such an extended basis lib.
+   Everything else, even if looks like stuff that could be in a basis lib,
+   but there is no module in *the* basis lib for it, should go into other
+   libraries.
+
+
+References
+----------
+
+  [1] The Standard ML Basis Library.
+      Emden R. Gansner and John H. Reppy.
+      Cambridge University Press, 2004.
+      ISBN 0521794781.