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Γ `
COM
c
:
Γ `
COM
x
:
Γ
(
x
)&
b
c
&
Γ
[
x7!
b
x
]
`
COM
e
0
:
b
0
&
'
0
Γ `
COM
fn
x
=>
e
0
:
'
0
b
x
!
b
0
&
Γ `
COM
e
1
:
Γ `
COM
e
2
:
'
0
b
2
!
b
0
&
'
1
b
2
&
'
2
Γ `
COM
e
1
e
2
:
b
0
&
'
1
;
'
2
;
'
0
Γ `
COM
channel
:
b
chan
fg
&
b
chan
fg
Γ `
COM
e
0
:
b
0
&
'
0
Γ `
COM
spawn
e
0
:
&
spawn
'
0
unit
Γ `
COM
e
1
:
Γ `
COM
e
2
:
b
chan
%
2
&
'
2
Γ `
COM
send
e
1
on
e
2
:
unit
&
'
1
;
'
2
;(
%
2
!
b
&
'
1
b
)
Γ `
COM
e
0
:
b
chan
%
0
&
'
0
Γ `
COM
receive
e
0
:
b
&
'
0
;(
%
0
?
b
)
Γ `
COM
e
:
b
&
'
0
and
' v '
0
if
b
b
Γ `
COM
e
:
0
&
'
0
b
Γ `
COM
e
:
b
&
'
Γ `
COM
e
:
8
(
1
; ;
n
)
:
b
if
1
; ;
n
do not occur free in
Γ
and
'
&
'
Γ `
COM
e
:
8
(
1
; ;
n
)
:
b
&
'
if
dom
(
)
f
1
;;
n
g
Γ `
COM
e
:(
b
)&
'
Table 4.
Communication Analysis:
Γ `
COM
e
:
b
&
'
(Example 11).
will be more intuitive to think of it as the empty string in regular expressions or
as the silent action in process calculi. The behaviour
'
1
;
'
2
says that
'
1
takes
place before
'
2
; this is
reminiscent of constructs in regular expressions as well as in process algebras.
The construct
'
2
whereas
'
1
+
'
2
indicates a choice between
'
1
and
rec
:'
indicates a recursive behaviour that acts as given by
'
except that any occurrence of
stands for
rec
:'
itself.
The behaviour
indicates that a new channel has been allocated for
communicating entities of type
chan
%
b
; the region
%
indicates the set of program
b
points
f
1
; ;
n
g
where the creation could have taken place. The behaviour
spawn
'
indicates that a new process has been generated and that it operates as
described by
'
. The construct
%
!
indicates that a value is sent over a channel of
b
type
indicates that a value is received over a channel of that
type; this is reminiscent of constructs in most process algebras (in particular
CSP).
chan
%
,and
%
?
b
b
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