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Extended Basis Library
This library implements a number of extensions to the signatures and
structures of the Standard ML Basis Library [1] as well as several
additional modules. The 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.
License: MLton license (a BSD-style license)
Portability: portable
Ported to: MLKit, MLton, Poly/ML, and SML/NJ
Stability: experimental
Maintainer: Vesa Karvonen <>
About Library Organization
This directory contains the documented signature definitions (*.sig)
and listings of all top-level bindings exported by this library
(export*.sml). The contents of this directory should ideally be
sufficient to understand the extensions provided by this library.
These build files define the extended basis library including all of
the original basis library. The idea is that users refer to one of
these, depending on the compiler, instead of the original basis
library. See the build files for further instructions.
These build files define only the extensions provided by this
library. Users may refer to these files, but they are probably more
interesting to maintainers. See the build files for further
This directory contains the implementation details of the library.
These directories (e.g. detail/ml/mlton/) contain compiler specific
implementation details. Different compilers implement different
subsets of the original basis library.
These directories (e.g. detail/smlnj/workarounds/) contain compiler
specific workarounds. The idea is that workarounds are separated
from other code so that once a compiler becomes more conforming to
the language definition and basis library specification, the
workarounds can be easily removed.
About Motivation and Scope
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 this library. As a rule of thumb, things that naturally belong to
specific basis library modules and what those things depend on should
go into this library. On the other hand, when there are several ways
to implement something with significantly different trade-offs, it
should most likely go into another library.
The signatures and structures defined by this library are not meant to
be cast in stone! We welcome contributions including new extensions,
bug fixes, and ports to new compilers. The recommended submit method
for small contributions to this library is to send a message with a
brief description of the proposed contribution as well as a patch
containing full code and documentation (signature comments) to either
the MLton-user list
or the MLton list .
For larger extensions or changes we recommend that you first contact
the active maintainer(s) of this library. The preferred contact method
is through the above mailing lists.
[1] The Standard ML Basis Library.
Emden R. Gansner and John H. Reppy.
Cambridge University Press, 2004.
ISBN 0521794781.