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--All rights reserved.
--
--Redistribution and use in source and binary forms, with or without
--modification, are permitted provided that the following conditions are
--met:
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-- distribution.
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-- names of its contributors may be used to endorse or promote products
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--THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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)abbrev domain VOID Void
++ Author: Stephen M. Watt, Gabriel Dos Reis
++ Date Created: 1986
++ Date Last Updated: October 5, 2009
++ Basic Operations:
++ Related Domains: ErrorFunctions, ResolveLatticeCompletion, Exit
++ Also See:
++ AMS Classifications:
++ Keywords: type, mode, coerce, no value
++ Examples:
++ References:
++ Description:
++ This type is used when no value is needed, e.g., in the \spad{then}
++ part of a one armed \spad{if}.
++ All values can be coerced to type Void. Once a value has been coerced
++ to Void, it cannot be recovered.
Void: CoercibleTo OutputForm with
void: () -> % ++ void() produces a void object.
== add
void() == voidValue()$Foreign(Builtin)
coerce(v:%) == empty()$OutputForm
import SetCategory
)abbrev domain EXIT Exit
++ Author: Stephen M. Watt
++ Date Created: 1986
++ Date Last Updated: May 30, 1991
++ Basic Operations:
++ Related Domains: ErrorFunctions, ResolveLatticeCompletion, Void
++ Also See:
++ AMS Classifications:
++ Keywords: exit, throw, error, non-local return
++ Examples:
++ References:
++ Description:
++ A function which does not return directly to its caller should
++ have Exit as its return type.
++
++ Note: It is convenient to have a formal \spad{coerce} into each type from
++ type Exit. This allows, for example, errors to be raised in
++ one half of a type-balanced \spad{if}.
Exit: SetCategory == add
coerce(n:%) == error "Cannot use an Exit value."
n1 = n2 == error "Cannot use an Exit value."
import Void
import Exit
)abbrev package RESLATC ResolveLatticeCompletion
++ Author: Stephen M. Watt
++ Date Created: 1986
++ Date Last Updated: May 30, 1991
++ Basic Operations:
++ Related Domains: ErrorFunctions, Exit, Void
++ Also See:
++ AMS Classifications:
++ Keywords: mode, resolve, type lattice
++ Examples:
++ References:
++ Description:
++ This package provides coercions for the special types \spadtype{Exit}
++ and \spadtype{Void}.
ResolveLatticeCompletion(S: Type): with
coerce: S -> Void
++ coerce(s) throws all information about s away.
++ This coercion allows values of any type to appear
++ in contexts where they will not be used.
++ For example, it allows the resolution of different types in
++ the \spad{then} and \spad{else} branches when an \spad{if}
++ is in a context where the resulting value is not used.
coerce: Exit -> S
++ coerce(e) is never really evaluated. This coercion is
++ used for formal type correctness when a function will not
++ return directly to its caller.
== add
coerce(s: S): Void == void()
coerce(e: Exit): S ==
error "Bug: Should not be able to obtain value of type Exit"
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