( load "ffs.met" )
;---------------------
;N sql.cam - rudimentary SQL-like operations on top of ffs.cam
;A J.N. Oliveira (jno@di.uminho.pt)
;D
; This is a CAMILA library for very rudimentary SQL-like operations
; whose semantics are specified on top of ffs.cam.
; This is expected to evolve towards  realistic CAMILA animation of a
; formal semantics of mSQL
;E
;
; sqlUpdate(ffs,c1,ue,c2,se) corresponds to the outcome of
; the SQL command "UPDATE ffs SET c1=ue WHERE se(c2)",
; where the update expression ue and the selection predicate se
; are provided as lambda-expressions.
;

( def _ops
  ( plus _ops
    ( makeff
      (
        ( quote sqlUpdate )
        ( quote
          (
            (
              ( SET FF A B )
              ( A )
              ( FF B B )
              ( A )
              ( FF A INT )
            )
            ( SET FF A B )
          )
        )
      )
    )
  )
)
;---------------------

( def sqlUpdate lambda
  ( ffs c1 ue c2 se )
  ( let
    (
      ( st
        ( set t
          ( from t ffs
            ( se
              ( ap t c2 )
            )
          )
        )
      )
      ( _
        ( princ "[ "
          ( card st ) " object(s) selected ]\n"
        )
      )
      ( rt
        ( difference ffs st )
      )
      ( update
        ( lambda
          ( t )
          ( let
            (
              ( v
                ( ap t c1 )
              )
            )
            ( plus t
              ( makeff
                ( c1
                  ( ue v )
                )
              )
            )
          )
        )
      )
    )
    ( union rt
      (
        ( lambda
          ( _y_ )
          ( set
            ( update _x_ )
            ( from _x_ _y_ )
          )
        ) st
      )
    )
  )
)
;---------------------
;
; sqlSelect(ffs,cs,c,se) specifies the outcome of
; SQL command " SELECT cs FROM ffs WHERE se(c) ",
; where the selection predicate se is provided as a lambda-expression.
;

( def _ops
  ( plus _ops
    ( makeff
      (
        ( quote sqlSelect )
        ( quote
          (
            (
              ( SET FF A B )
              ( SET A )
              ( A )
              ( FF A INT )
            )
            ( SET FF A B )
          )
        )
      )
    )
  )
)
;---------------------

( def sqlSelect lambda
  ( ffs cs c se )
  ( let
    (
      ( st
        ( set t
          ( from t ffs
            ( se
              ( ap t c )
            )
          )
        )
      )
      ( _
        ( princ "[ "
          ( card st ) " object(s) selected ]\n"
        )
      )
      ( project
        ( lambda
          ( t )
          ( dr t cs )
        )
      )
    )
    (
      ( lambda
        ( _y_ )
        ( set
          ( project _x_ )
          ( from _x_ _y_ )
        )
      ) st
    )
  )
)
;---------------------
;
; sqlDelete(ffs,c,se) specifies the outcome of
; SQL command "DELETE FROM ffs WHERE se(c) ",
; where the selection predicate se is provided as a lambda-expression.
;

( def _ops
  ( plus _ops
    ( makeff
      (
        ( quote sqlDelete )
        ( quote
          (
            (
              ( SET FF A B )
              ( A )
              ( FF A INT )
            )
            ( SET FF A B )
          )
        )
      )
    )
  )
)
;---------------------

( def sqlDelete lambda
  ( ffs c se )
  ( let
    (
      ( st
        ( set t
          ( from t ffs
            ( not
              ( se
                ( ap t c )
              )
            )
          )
        )
      )
      ( _
        ( princ "[ "
          ( card
            ( difference ffs st )
          ) " object(s) deleted ]\n"
        )
      )
    ) st
  )
)
;---------------------