SML '97 Conversion Guide

Introduction

The primary goal of this document is to help current SML programmers learn to use SML '97 (as implemented in SML/NJ 110), and to help them convert old SML code to SML '97. It concentrates on changes in the language and libraries, and assumes some familiarity with SML. However, it should also be of some use to new SML programmers, as a supplement to one of the available textbooks or tutorials.

The new SML '97 language itself is defined in The Definition of Standard ML (Revised), hereafter refered to as "the Definition". Appendix G of that book briefly summarizes the language changes, mainly from the point of view of the language semantics. The treatment here expands on that description, taking the point of view of a programmer. Note that the second editions of Paulson's and Ullman's books describe SML '97.

The other major changes are encompassed in an extensive new Basis library that replaces the minimal initial basis described in Appendices C and D of the original SML '90 Definition.

1. Language Changes

This section is a more detailed exploration of the changes summarized in appendix G of the new Definition.

• 1.1. Types and Type Checking

  • 1.1.2. Type checking

    1.1.2.1. Value polymorphism
    1.1.2.2. Overloaded literals
    1.1.2.3. Defaulting overloads

  • 1.1.3. Explicit type variable binding

  • 1.1.4. Local datatypes

  • 1.1.5. Datatype replication declarations

  • 1.1.6. real not an equality type

• 1.2. Core Language

  • 1.2.1. Rebinding constructor names with val rec and fun

  • 1.2.2. Revised infix operator precedence rules

  • 1.2.3. Forbidden rebindings

• 1.3. Modules

  1.3.1. Type abbreviations in signatures

  1.3.2. Datatype replication specs

  1.3.3. Adding definitions with where type

  1.3.4. Restriction of sharing to local paths

  1.3.5. Noninterference of sharing and definitional specs

  1.3.6. Replacement of "definitional" sharing by definitional specs

  1.3.7. Structure sharing as derived form for type sharing

  1.3.8. include sigexp

  1.3.9. opaque signature matching (:>)

  1.3.10. equality type specs, inferred equality properties

  1.3.11. open and local specification forms deleted

  1.3.12. no repeated specifications of an identifier

  1.3.13. behavior of include (Defn vs SML/NJ)

• 1.4. SML/NJ Deviations

  1.4.1. val rec syntax

  1.4.2. withtype scoping rules

• 1.5. SML/NJ Extensions: Core

  1.5.1. or patterns

  1.5.2. vector expressions and patterns

• 1.6. SML/NJ Extensions: Modules

  1.6.1. higher-order functors

  1.6.2. structure definition specs

  1.6.3. where clause for structure definitions

  1.6.4. Layered Redefinitions Ignored

  1.6.5. type spec merging with include

2. Library and Environment Changes

• 2.1. Basic Types

  2.1.1. Arithmetic

  2.1.2. Characters and Strings

  2.1.3. Lists

• 2.2. Input/Output

  2.2.1. TextIO

  2.2.2. The print function

• 2.3. System Facilities

  2.3.1. Invoking the compiler

  2.3.2. OS structure in Basis

  2.3.3. Posix structure in Basis

  2.3.4. The Unix structure

• 2.4. SML/NJ Facilities

  2.4.1. The SMLofNJ Structure

  2.4.2. Useful control flags