Notes on Compatibility

The sample programs rely on the Standard ML Basis Library.

Starting with Chapter 7, they also rely (to a minor extent) on recent changes to ML itself. I am distributing the code in a form suitable for up-to-date ML compilers, alongside versions of the programs for chapters 3, 8 and 10 for use with older compilers.Older compilers (pre-1998) might be incompatible in three respects:

• Instead of Real.==(x,y), they might use x=y to test equality on real numbers. This affects code for Chapter 3.
• Instead of value polymorphism, they might have weak (imperative) type variables such as '_a. (Chapters 8 and 10.)
• Instead of the :> syntax, they might use the abstraction keyword to indicate opaque signature constraints. (Chapters 8 and 10.)

Complicating matters further, in 2004 the ML Basis Library was modified slightly. Compilers compliant with the changes reject a few of the functions presented in the book. To address this issue, post-2004 versions of the code for chapters 8 and 9 are provided.

• The function Substring.all was renamed to Substring.full
• The type of the function TextIO.inputLine was changed to return a string option rather than a string. It now returns NONE if the input stream has run out.

Later chapters sometimes refer to code presented in earlier chapters. However, if you compile the code for all the chapters in order, there should be no compilation errors.

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