VDM-10 Language Manual

Chapter 13. Statements
block returns a value, the evaluation of the block statement is terminated when the last statement
in the block has been evaluated. When the block statement is left the values of the
local variables are discharged. Thus, the scope of these variables is simply inside the block
statement.
Examples: In the context of a VDM-SL state definition
✞
✡✝
state St of
x: nat
y: nat
l: seq1 of nat
end
or in the context of a VDM++ instance variables
✞
✡✝
instance variables
x: nat;
y: nat;
l: seq1 of nat;
the operation Swap uses a block statement to swap the values of variables x and y:
✞
✡✝
Swap : () ==> ()
Swap () ==
(dcl temp: nat := x;
x := y;
y := temp
)
✆
✆
✆
13.4 The Assignment Statement
Syntax: statement = . . .
| general assign statement
| . . . ;
general assign statement = assign statement
| multiple assign statement ;
assign statement = state designator, ‘:=’, expression ;
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