The Standard ML Basis Library

The General structure

Synopsis

signature GENERAL
structure General :> GENERAL

The structure General defines exceptions, datatypes, and functions which are used throughout the SML Basis Library, and are useful in a wide range of programs.

All of the types and values defined in General are available unqualified at the top-level.

Interface

eqtype unit
type exn = exn

exception Bind
exception Match
exception Chr
exception Div
exception Domain
exception Fail of string
exception Overflow
exception Size
exception Span
exception Subscript

val exnName : exn -> string
val exnMessage : exn -> string

datatype order = LESS | EQUAL | GREATER
val ! : 'a ref -> 'a
val := : 'a ref * 'a -> unit
val o : ('b -> 'c) * ('a -> 'b) -> 'a -> 'c
val before : 'a * unit -> 'a
val ignore : 'a -> unit

Description

eqtype unit
The type containing a single value denoted (), which is typically used as a trivial argument or as a return value for a side-effecting function.

type exn = exn
The type of values transmitted when an exception is raised and handled. This type is special in that it behaves like a datatype with an extensible set of data constructors, where new constructors are created by exception declarations.

exception Bind
exception Match
Exceptions indicating that pattern matching failed in a val binding or, respectively, in a case expression or function application. This occurs when the matched value is not an instance of any of the supplied patterns.

exception Chr
The exception indicating an attempt to create a character with a code outside the range supported by the underlying character type (see CHAR.chr).

exception Div
The exception indicating an attempt to divide by zero. It replaces the Mod exception required by the SML'90 Definition.

exception Domain
The exception indicating that the argument of a mathematical function is outside the domain of the function. It is raised by functions in structures matching the MATH or INT_INF signatures. It replaces the Sqrt and Ln exceptions required by the SML'90 Definition.

exception Fail of string
A general-purpose exception used to signify the failure of an operation. It is not raised by any function in the SML Basis Library, but is provided for use by users and user-defined libraries.

exception Overflow
The exception indicating that the result of an arithmetic function is not representable, in particular, is too large. It replaces the Abs, Exp, Neg, Prod, Quot, and Sum exceptions required by the SML'90 Definition.

exception Size
The exception indicating an attempt to create an aggregate data structure (such as an array, string, or vector) whose size is too large or negative.

exception Span
The exception indicating an attempt to apply SUBSTRING.span to two incompatible substrings.

exception Subscript
The exception indicating that an index is out of range, typically arising when the program is accessing an element in an aggregate data structure (such as a list, string, array, or vector).

exnName ex
returns a name for the exception ex. The name returned may be that of any exception constructor aliasing with ex. For instance, 
let exception E1; exception E2 = E1 in exnName E2 end
might evaluate to "E1" or "E2".

exnMessage ex
returns a message corresponding to exception ex. The precise format of the message may vary between implementations and locales, but will at least contain the string exnName ex.
Example:
exnMessage Div = "Div"
exnMessage (OS.SysErr ("No such file", NONE)) = 
  "OS.SysErr \"No such file\""


datatype order = LESS | EQUAL | GREATER
Values of type order are used when comparing elements of a type that has a linear ordering.

! re
returns the value referred to by the reference re.

re := a
makes the reference re refer to the value a.

f o g
is the function composition of f and g. Thus, (f o g) a is equivalent to f(g a).

a before b
returns a. It provides a notational shorthand for evaluating a, then b, before returning the value of a.

ignore a
returns (). The purpose of ignore is to discard the result of a computation, returning () instead. This is useful, for example, when a higher-order function, such as List.app, requires a function returning unit, but the function to be used returns values of some other type.

Discussion

Some systems may provide a compatibility mode in which the exceptions replaced from SML'90 (e.g., Abs, Sqrt) are provided at top-level as aliases for the new exceptions.

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Generated October 02, 2003
Last Modified February 20, 1997
Comments to John Reppy.

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