General structure

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The General structure provides the fundamental types unit, exn, and order, the standard exceptions raised by the runtime, and a few utility functions. Its contents are available without qualification in every Morel program.

Specified by the Standard ML Basis Library.

Synopsis

type unit
type exn = exn
datatype order = LESS | EQUAL | GREATER

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
val o : ('b -> 'c) * ('a -> 'b) -> 'a -> 'c
val before : 'a * unit -> 'a
val ignore : 'a -> unit
val ! : 'a ref -> 'a val := : 'a ref * 'a -> unit

type unit

is the type that contains the single value (). It is used as the result type of functions called for side effects.

type exn

is the type of exceptions. Every exception constructor creates a value of this type, and the raise and handle constructs operate on it.

datatype order

exception Bind

is raised when pattern matching fails in a val binding.

exception Match

is raised when pattern matching fails in a case expression or function application.

exception Chr

is raised by Char.chr when given an integer outside the valid range.

exception Div

is raised on integer division by zero.

exception Domain

is raised when a function is applied outside its domain.

exception Fail

is a general-purpose exception carrying a descriptive message string.

exception Overflow

is raised when an integer arithmetic result is too large to represent.

exception Size

is raised when a size argument is negative or exceeds the maximum allowed.

exception Span

is raised when an invalid source span is supplied.

exception Subscript

is raised when a sequence index is out of bounds.

exnName

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

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""

o

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

before

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

ignore

ignore x always returns unit. The function evaluates its argument but throws away the value.

!

``

Not yet implemented.