illo

पिछला वर्षdiscuss

Standard ML program. I fear it does not contribute much to the conversation but I cannot abstain from calling attention to my favourite pragmatic programming language that is presently on what seems to be a neverending life support.

  structure I = Int
  structure S = String
  structure SU = Substring
  structure SC = StringCvt
  
  infix 5 >>
  fun (x >> y) f = if x = y then () else (f x; ((x + 1) >> y) f)
  
  val printRow =
  let
      val p0 = SC.padLeft #"0" val ps = SC.padLeft #" "
      val td = I.fmt SC.DEC val tx = I.fmt SC.HEX
      val to = I.fmt SC.OCT val tb = I.fmt SC.BIN
      val desc = fn
            0 => "NUL" | 1 => "SOH" | 2 => "STX" | 3 => "ETX" | 4 => "EOT" | 5 => "ENQ"
          | 6 => "ACK" | 7 => "BEL" | 8 => "BS" | 9 => "HT" | 10 => "LF" | 11 => "VT"
          | 12 => "FF" | 13 => "CR" | 14 => "SO" | 15 => "SI" | 16 => "DLE" | 17 => "DC1"
          | 18 => "DC2" | 19 => "DC3" | 20 => "DC4" | 21 => "NAK" | 22 => "SYN" | 23 => "ETB"
          | 24 => "CAN" | 25 => "EM" | 26 => "SUB" | 27 => "ESC" | 28 => "FS" | 29 => "GS"
          | 30 => "RS" | 31 => "US" | 32 => "SPC" | 127 => "DEL" | n => str (chr n)
  in
      fn n => print (S.concatWith " " [ps 3 (td n), p0 2 (tx n), p0 7 (tb n), p0 3 (to n), desc n] ^ "\n")
  end
  
  val spec =
  let
      val scan = fn rad => fn sl => SC.scanString (I.scan rad) (implode sl)
  in
      fn str => valOf (case explode str of
        #"0" :: #"x" :: hex => scan SC.HEX hex
      | #"0" :: #"o" :: oct => scan SC.OCT oct
      | #"0" :: #"b" :: bin => scan SC.BIN bin
      | dec => scan SC.DEC dec)
  end
  
  val () = case CommandLine.arguments () of
        [] => (0 >> 128) printRow
      | [req] => printRow (spec req)
      | _ => raise Fail "arguments"

illo

3 वर्ष पहलेdiscuss

> [ a = b ] && echo "Oops!" || echo "Expected; phew!"

Not to be taken as a general rule though. I might be mistaken but I think that bash would parse the line as:

  ([ a = b ] && echo "Oops!") || echo "Expected; phew!"

so if the command sequence after `&&` fails, then the code sequence after `||` is executed anyway:

  illo@joe:~ $ [ "a" == "a" ] && >/dev/full echo "strings match" || echo "strings don't match"
  -bash: echo: write error: No space left on device
  strings don't match
  illo@joe:~ $

This is different from the semantics of the `if` block:

  illo@joe:~ $ if [ "a" == "a" ]; then >/dev/full echo "strings match"; else echo "strings don't match"; fi
  -bash: echo: write error: No space left on device
  illo@joe:~ $

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