1 Use monads to structure the passing of state??

2 do { var <- expr

3 ; some action in the monad of choice

4 ; return value }

5

6 -- ????

7 expr >>= \var . some_action >>= \dummy . return value

8

9 [ ch1 <- next. ch2 <- next. return: foo ] `with: s.

10

11 [ {socket:. state:. len:. index:} <- read.

12 ???

13

14 in s { ch1 <- next

15 ; ch2 <- next

16 ; return foo }

17

18

19

20

21

22 SocketCharProvider <- {socket: Nil. state: ''. len: 0. index: 0}.

23

24 self@SocketCharProvider newOn: socket [

25 self \ { socket: socket }.

26 ].

27

28 self@SocketCharProvider next [

29 {socket:. state:. len:. index:} <- self.

30 state == EOF ifTrue: [ ^ {state. self} ].

31 index >= len ifFalse: [ ^ {state at: index. self \ {index: index + 1}} ].

32

33 newState <- socket read.

34 newState

35 ifNil: [ (self \ {state: EOF. len: 0. index: 0}) next ]

36 ifNotNil: [ (self \ {state: newState. len: newState size. index: 0}) next ].

37 ]

38

39 {ch1. s} <- s next.

40 {ch2. s} <- s next.

41

42

43

44

45

46 SocketCharProvider <- {socket: Nil. state: Nil}.

47

48 self@SocketCharProvider newOn: socket [

49 self \ { socket: socket. state: {buf: ''. len: 0. index: 0} ref }.

50 ].

51

52 self@SocketCharProvider next [

53 {socket:. state:.} <- self.

54 [

55 [

56 {buf:. len:. index:.} <- state read.

57 buf == EOF ifTrue: [ ^ buf ].

58 index >= len ifFalse: [ state write: state peek \ { index: index + 1 }. ^ buf at: index ].

59

60 newState <- socket read.

61 newState

62 ifNil: [ state write: {buf: EOF. len: 0. index: 0} ]

63 ifNotNil: [ state write: {buf: newState. len: newState size. index: 0} ].

64 ] loop.

65 ] transaction.

66 ]

67

68 ch1 <- s next.

69 ch2 <- s next.

70

71

72

73 Globals at: #ThingSDL put: {super*: SDL.}.

74

75 self@ThingSDL delay: ms

76 [

77 nextEventTime <- Time now + (ms / 1000.0).

78 result <- SDLNet checkSockets (self socketSet) 0.

79 (result isNotNil and: [result isPositive])

80 ifTrue: [

81 {ready. unready} <- self activeSockets partition: [ record | record key isReady ].

82 self activeSockets: unready.

83 ready do: [ record |

84 sock <- record key.

85 suspension <- record value.

86 self socketSet delSocket: sock.

87 metalevel resume: suspension with: sock

88 ]

89 ].

90 metalevel runRunnableSuspensionsUntil: nextEventTime.

91 ]