1 //: Go from an address to the payload it points at (skipping the refcount)
  2 //: using /lookup.
  3 //:
  4 //: Let's say we have this address (read the top of the address layer for
  5 //: details on these diagrams):
  6 //:
  7 //:                     +---+------------+
  8 //:          x -------> | 1 |  number    |
  9 //:                     +---+------------+
 10 //:
 11 //: Once you have an address you can read or modify its payload by performing
 12 //: a lookup:
 13 //:
 14 //:     x/lookup <- copy 34
 15 //:
 16 //: or more concisely:
 17 //:
 18 //:     *x <- copy 34
 19 //:
 20 //: This modifies not x, but the payload x points to:
 21 //:
 22 //:                     +---+------------+
 23 //:          x -------> | 1 |         34 |
 24 //:                     +---+------------+
 25 //:
 26 //: You can also read from the payload in instructions like this:
 27 //:
 28 //:     z:num <- add *x, 1
 29 //:
 30 //: After this instruction runs the value of z will be 35.
 31 //:
 32 //: The tests in this layer use unsafe operations so as to stay decoupled from
 33 //: 'new'.
 34 
 35 :(scenario copy_indirect)
 36 def main [
 37   1:address:num <- copy 10/unsafe
 38   11:num <- copy 34
 39   # This loads location 1 as an address and looks up *that* location.
 40   2:num <- copy 1:address:num/lookup
 41 ]
 42 # 1 contains 10. Skip refcount and lookup location 11.
 43 +mem: storing 34 in location 2
 44 
 45 :(before "End Preprocess read_memory(x)")
 46 canonize(x);
 47 
 48 //: similarly, write to addresses pointing at other locations using the
 49 //: 'lookup' property
 50 :(scenario store_indirect)
 51 def main [
 52   1:address:num <- copy 10/unsafe
 53   1:address:num/lookup <- copy 34
 54 ]
 55 +mem: storing 34 in location 11
 56 
 57 :(before "End Preprocess write_memory(x, data)")
 58 canonize(x);
 59 
 60 //: writes to address 0 always loudly fail
 61 :(scenario store_to_0_fails)
 62 % Hide_errors = true;
 63 def main [
 64   1:address:num <- copy 0
 65   1:address:num/lookup <- copy 34
 66 ]
 67 -mem: storing 34 in location 0
 68 +error: can't write to location 0 in '1:address:num/lookup <- copy 34'
 69 
 70 //: attempts to /lookup address 0 always loudly fail
 71 :(scenario lookup_0_fails)
 72 % Hide_errors = true;
 73 def main [
 74   1:address:num <- copy 0
 75   2:num <- copy 1:address:num/lookup
 76 ]
 77 +error: tried to /lookup 0 in '2:num <- copy 1:address:num/lookup'
 78 
 79 :(code)
 80 void canonize(reagent& x) {
 81   if (is_literal(x)) return;
 82   // End canonize(x) Special-cases
 83   while (has_property(x, "lookup"))
 84   ¦ lookup_memory(x);
 85 }
 86 
 87 void lookup_memory(reagent& x) {
 88   .nonzero(diff == -char)[0]
    idx -= 1
    line[idx] = 0
    return changed

count = 0
while True:
    count += 1
    changed = False
    for row in cucumbers[:]:
        changed |= shift(row, 1)
    for col in cucumbers.T:
        changed |= shift(col, 3)
    if not changed:
        print(count)
        break