NICE Language Committee: ms-multbranch
From Michael Schweitzer
Date: Sat, 16 Apr 94 15:10:53 +0200
To: bertrand@eiffel.com
Subject: MS-MULTI_BRANCH-SYNTAX
Cc: tynor@atlanta.twr.com
Content-Length: 2137
Status: RO
X-Lines: 85
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Key : MS-MULTI_BRANCH-SYNTAX
Title : Two proposals on the syntax of multi branch instructions.
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As an exception to the general rule, I've bundeled two proposals
into one message, since they are closely related.
A)
Discussion:
The list of constants and/or intervals in the 'when' part
of an inspect instruction is optional, i.e. the instruction
inspect i
when then
something
...
end
is legal.
Question:
Does this serve any useful purpose? As far as I know, ISE's
compiler rejects this as does our compiler.
Proposal A:
The syntax for 'Choices' should be changed to
Choices = {Choice "," ...}+
i.e. there should be at least one 'Choice'.
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B)
Discussion:
It is not allowed to use constant attributes in an interval,
since, for example, 'Integer_interval' is defined as
Integer_interval = Integer_constant ".." Integer_constant
and 'Integer_constant' covers manifest constants of type INTEGER
only (pages 387, 568).
Therefore the instruction
inspect i
when Red .. Yellow then
something
...
end
is syntactically illegal. Since Bertrand uses this (illegal)
form in ETL (page 265) I suppose he did not intend to re-
strict intervals to manifest constants only.
Proposal B:
I propose changing the syntax of 'Integer_interval' and
'Character_interval' as follows:
Integer_interval = Integer_inspect_constant ".."
Integer_inspect_constant
Character_interval = Character_inspect_constant ".."
Character_inspect_constant
and
Integer_inspect_constant = Constant
Character_inspect_constant = Constant
with the additional rule that an 'Integer_inspect_constant'
must be of type INTEGER, a 'Character_inspect_constant' of type
CHARACTER.
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Best regards,
Michael
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