# Mu - 040brace.cc

      1 //: Structured programming
      2 //:
      3 //: Our jump recipes are quite inconvenient to use, so Mu provides a
      4 //: lightweight tool called 'transform_braces' to work in a slightly more
      5 //: convenient format with nested braces:
      6 //:
      7 //:   {
      8 //:     some instructions
      9 //:     {
     10 //:       more instructions
     11 //:     }
     12 //:   }
     13 //:
     14 //: Braces are just labels, they require no special parsing. The pseudo
     15 //: instructions 'loop' and 'break' jump to just after the enclosing '{' and
     16 //: '}' respectively.
     17 //:
     18 //: Conditional and unconditional 'loop' and 'break' should give us 80% of the
     19 //: benefits of the control-flow primitives we're used to in other languages,
     20 //: like 'if', 'while', 'for', etc.
     21
     22 :(scenarios transform)
     23 :(scenario brace_conversion)
     24 def main [
     25   {
     26     break
     27     1:num <- copy 0
     28   }
     29 ]
     30 +transform: --- transform braces for recipe main
     31 +transform: jump 1:offset
     32 +transform: copy ...
     33
     34 :(before "End Instruction Modifying Transforms")
     35 Transform.push_back(transform_braces);  // idempotent
     36
     37 :(code)
     38 void transform_braces(const recipe_ordinal r) {
     39   const bool OPEN = false, CLOSE = true;
     40   // use signed integer for step index because we'll be doing arithmetic on it
     41   list<pair<bool/*OPEN/CLOSE*/, /*step*/int> > braces;
     42   trace(9991, "transform") << "--- transform braces for recipe " << get(Recipe, r).name << end();
     43   for (int index = 0;  index < SIZE(get(Recipe, r).steps);  ++index) {
     44     const instruction& inst = get(Recipe, r).steps.at(index);
     45     if (inst.label == "{") {
     46       trace(9993, "transform") << maybe(get(Recipe, r).name) << "push (open, " << index << ")" << end();
     47       braces.push_back(pair<bool,int>(OPEN, index));
     48     }
     49     if (inst.label == "}") {
     50       trace(9993, "transform") << "push (close, " << index << ")" << end();
     51       braces.push_back(pair<bool,int>(CLOSE, index));
     52     }
     53   }
     54   stack</*step*/int> open_braces;
     55   for (int index = 0;  index < SIZE(get(Recipe, r).steps);  ++index) {
     56     instruction& inst = get(Recipe, r).steps.at(index);
     57     if (inst.label == "{") {
     58       open_braces.push(index);
     59       continue;
     60     }
     61     if (inst.label == "}") {
     62       if (open_braces.empty()) {
     63         raise << maybe(get(Recipe, r).name) << "unbalanced '}'\n" << end();
     64         return;
     65       }
     66       open_braces.pop();
     67       continue;
     68     }
     69     if (inst.is_label) continue;
     70     if (inst.name != "loop"
     71          && inst.name != "loop-if"
     72          && inst.name != "loop-unless"
     73          && inst.name != "break"
     74          && inst.name != "break-if"
     75          && inst.name != "break-unless") {
     76       trace(9992, "transform") << inst.name << " ..." << end();
     77       continue;
     78     }
     79     // check for errors
     80     if (inst.name.find("-if") != string::npos || inst.name.find("-unless") != string::npos) {
     81       if (inst.ingredients.empty()) {
     82         raise << maybe(get(Recipe, r).name) << "'" << inst.name << "' expects 1 or 2 ingredients, but got none\n" << end();
     83         continue;
     84       }
     85     }
     86     // update instruction operation
     87     string old_name = inst.name;  // save a copy
     88     if (inst.name.find("-if") != string::npos) {
     89       inst.name = "jump-if";
     90       inst.operation = JUMP_IF;
     91     }
     92     else if (inst.name.find("-unless") != string::npos) {
     93       inst.name = "jump-unless";
     94       inst.operation = JUMP_UNLESS;
     95     }
     96     else {
     97       inst.name = "jump";
     98       inst.operation = JUMP;
     99     }
    100     // check for explicitly provided targets
    101     if (inst.name.find("-if") != string::npos || inst.name.find("-unless") != string::npos) {
    102       // conditional branches check arg 1
    103       if (SIZE(inst.ingredients) > 1 && is_literal(inst.ingredients.at(1))) {
    104         trace(9992, "transform") << inst.name << ' ' << inst.ingredients.at(1).name << ":offset" << end();
    105         continue;
    106       }
    107     }
    108     else {
    109       // unconditional branches check arg 0
    110       if (!inst.ingredients.empty() && is_literal(inst.ingredients.at(0))) {
    111         trace(9992, "transform") << "jump " << inst.ingredients.at(0).name << ":offset" << end();
    112         continue;
    113       }
    114     }
    115     // if implicit, compute target
    116     reagent target(new type_tree("offset"));
    117     target.set_value(0);
    118     if (open_braces.empty())
    119       raise << maybe(get(Recipe, r).name) << "'" << old_name << "' needs a '{' before\n" << end();
    120     else if (old_name.find("loop") != string::npos)
    121       target.set_value(open_braces.top()-index);
    122     else  // break instruction
    123       target.set_value(matching_brace(open_braces.top(), braces, r) - index - 1);
    124     inst.ingredients.push_back(target);
    125     // log computed target
    126     if (inst.name == "jump")
    127       trace(9992, "transform") << "jump " << no_scientific(target.value) << ":offset" << end();
    128     else
    129       trace(9992, "transform") << inst.name << ' ' << inst.ingredients.at(0).name << ", " << no_scientific(target.value) << ":offset" << end();
    130   }
    131 }
    132
    133 // returns a signed integer not just so that we can return -1 but also to
    134 // enable future signed arithmetic
    135 int matching_brace(int index, const list<pair<bool, int> >& braces, recipe_ordinal r) {
    136   int stacksize = 0;
    137   for (list<pair<bool, int> >::const_iterator p = braces.begin();  p != braces.end();  ++p) {
    138     if (p->second < index) continue;
    139     stacksize += (p->first ? 1 : -1);
    140     if (stacksize == 0) return p->second;
    141   }
    142   raise << maybe(get(Recipe, r).name) << "unbalanced '{'\n" << end();
    143   return SIZE(get(Recipe, r).steps);  // exit current routine
    144 }
    145
    146 :(scenario loop)
    147 def main [
    148   1:num <- copy 0
    149   2:num <- copy 0
    150   {
    151     3:num <- copy 0
    152     loop
    153   }
    154 ]
    155 +transform: --- transform braces for recipe main
    156 +transform: copy ...
    157 +transform: copy ...
    158 +transform: copy ...
    159 +transform: jump -2:offset
    160
    161 :(scenario break_empty_block)
    162 def main [
    163   1:num <- copy 0
    164   {
    165     break
    166   }
    167 ]
    168 +transform: --- transform braces for recipe main
    169 +transform: copy ...
    170 +transform: jump 0:offset
    171
    172 :(scenario break_cascading)
    173 def main [
    174   1:num <- copy 0
    175   {
    176     break
    177   }
    178   {
    179     break
    180   }
    181 ]
    182 +transform: --- transform braces for recipe main
    183 +transform: copy ...
    184 +transform: jump 0:offset
    185 +transform: jump 0:offset
    186
    187 :(scenario break_cascading_2)
    188 def main [
    189   1:num <- copy 0
    190   2:num <- copy 0
    191   {
    192     break
    193     3:num <- copy 0
    194   }
    195   {
    196     break
    197   }
    198 ]
    199 +transform: --- transform braces for recipe main
    200 +transform: copy ...
    201 +transform: copy ...
    202 +transform: jump 1:offset
    203 +transform: copy ...
    204 +transform: jump 0:offset
    205
    206 :(scenario break_if)
    207 def main [
    208   1:num <- copy 0
    209   2:num <- copy 0
    210   {
    211     break-if 2:num
    212     3:num <- copy 0
    213   }
    214   {
    215     break
    216   }
    217 ]
    218 +transform: --- transform braces for recipe main
    219 +transform: copy ...
    220 +transform: copy ...
    221 +transform: jump-if 2, 1:offset
    222 +transform: copy ...
    223 +transform: jump 0:offset
    224
    225 :(scenario break_nested)
    226 def main [
    227   1:num <- copy 0
    228   {
    229     2:num <- copy 0
    230     break
    231     {
    232       3:num <- copy 0
    233     }
    234     4:num <- copy 0
    235   }
    236 ]
    237 +transform: jump 4:offset
    238
    239 :(scenario break_nested_degenerate)
    240 def main [
    241   1:num <- copy 0
    242   {
    243     2:num <- copy 0
    244     break
    245     {
    246     }
    247     4:num <- copy 0
    248   }
    249 ]
    250 +transform: jump 3:offset
    251
    252 :(scenario break_nested_degenerate_2)
    253 def main [
    254   1:num <- copy 0
    255   {
    256     2:num <- copy 0
    257     break
    258     {
    259     }
    260   }
    261 ]
    262 +transform: jump 2:offset
    263
    264 :(scenario break_label)
    265 % Hide_errors = true;
    266 def main [
    267   1:num <- copy 0
    268   {
    269     break +foo:offset
    270   }
    271 ]
    272 +transform: jump +foo:offset
    273
    274 :(scenario break_unless)
    275 def main [
    276   1:num <- copy 0
    277   2:num <- copy 0
    278   {
    279     break-unless 2:num
    280     3:num <- copy 0
    281   }
    282 ]
    283 +transform: --- transform braces for recipe main
    284 +transform: copy ...
    285 +transform: copy ...
    286 +transform: jump-unless 2, 1:offset
    287 +transform: copy ...
    288
    289 :(scenario loop_unless)
    290 def main [
    291   1:num <- copy 0
    292   2:num <- copy 0
    293   {
    294     loop-unless 2:num
    295     3:num <- copy 0
    296   }
    297 ]
    298 +transform: --- transform braces for recipe main
    299 +transform: copy ...
    300 +transform: copy ...
    301 +transform: jump-unless 2, -1:offset
    302 +transform: copy ...
    303
    304 :(scenario loop_nested)
    305 def main [
    306   1:num <- copy 0
    307   {
    308     2:num <- copy 0
    309     {
    310       3:num <- copy 0
    311     }
    312     loop-if 4:bool
    313     5:num <- copy 0
    314   }
    315 ]
    316 +transform: --- transform braces for recipe main
    317 +transform: jump-if 4, -5:offset
    318
    319 :(scenario loop_label)
    320 def main [
    321   1:num <- copy 0
    322   +foo
    323   2:num <- copy 0
    324 ]
    325 +transform: --- transform braces for recipe main
    326 +transform: copy ...
    327 +transform: copy ...
    328
    329 //: test how things actually run
    330 :(scenarios run)
    331 :(scenario brace_conversion_and_run)
    332 def test-factorial [
    333   1:num <- copy 5
    334   2:num <- copy 1
    335   {
    336     3:bool <- equal 1:num, 1
    337     break-if 3:bool
    338 #    $print 1:num
    339     2:num <- multiply 2:num, 1:num
    340     1:num <- subtract 1:num, 1
    341     loop
    342   }
    343   4:num <- copy 2:num  # trigger a read
    344 ]
    345 +mem: location 2 is 120
    346
    347 :(scenario break_outside_braces_fails)
    348 % Hide_errors = true;
    349 def main [
    350   break
    351 ]
    352 +error: main: 'break' needs a '{' before
    353
    354 :(scenario break_conditional_without_ingredient_fails)
    355 % Hide_errors = true;
    356 def main [
    357   {
    358     break-if
    359   }
    360 ]
    361 +error: main: 'break-if' expects 1 or 2 ingredients, but got none
    362
    363 //: Using break we can now implement conditional returns.
    364
    365 :(scenario return_if)
    366 def main [
    367   1:num <- test1
    368 ]
    369 def test1 [
    370   return-if 0, 34
    371   return 35
    372 ]
    373 +mem: storing 35 in location 1
    374
    375 :(scenario return_if_2)
    376 def main [
    377   1:num <- test1
    378 ]
    379 def test1 [
    380   return-if 1, 34
    381   return 35
    382 ]
    383 +mem: storing 34 in location 1
    384
    385 :(before "End Rewrite Instruction(curr, recipe result)")
    386 // rewrite 'return-if a, b, c, ...' to
    387 //   ```
    388 //   {
    389 //     break-unless a
    390 //     return b, c, ...
    391 //   }
    392 //   ```
    393 if (curr.name == "return-if" || curr.name == "reply-if") {
    394   if (curr.products.empty()) {
    395     emit_return_block(result, "break-unless", curr);
    396     curr.clear();
    397   }
    398   else {
    399     raise << "'" << curr.name << "' never yields any products\n" << end();
    400   }
    401 }
    402 // rewrite 'return-unless a, b, c, ...' to
    403 //   ```
    404 //   {
    405 //     break-if a
    406 //     return b, c, ...
    407 //   }
    408 //   ```
    409 if (curr.name == "return-unless" || curr.name == "reply-unless") {
    410   if (curr.products.empty()) {
    411     emit_return_block(result, "break-if", curr);
    412     curr.clear();
    413   }
    414   else {
    415     raise << "'" << curr.name << "' never yields any products\n" << end();
    416   }
    417 }
    418
    419 :(code)
    420 void emit_return_block(recipe& out, const string& break_command, const instruction& inst) {
    421   const vector<reagent>& ingredients = inst.ingredients;
    422   reagent/*copy*/ condition = ingredients.at(0);
    423   vector<reagent> return_ingredients;
    424   copy(++ingredients.begin(), ingredients.end(), inserter(return_ingredients, return_ingredients.end()));
    425
    426   // {
    427   instruction open_label;  open_label.is_label=true;  open_label.label = "{";
    428   out.steps.push_back(open_label);
    429
    430   // <break command> <condition>
    431   instruction break_inst;
    432   break_inst.operation = get(Recipe_ordinal, break_command);
    433   break_inst.name = break_command;
    434   break_inst.ingredients.push_back(condition);
    435   out.steps.push_back(break_inst);
    436
    437   // return <return ingredients>
    438   instruction return_inst;
    439   return_inst.operation = get(Recipe_ordinal, "return");
    440   return_inst.name = "return";
    441   return_inst.ingredients.swap(return_ingredients);
    442   return_inst.original_string = inst.original_string;
    443   out.steps.push_back(return_inst);
    444
    445   // }
    446   instruction close_label;  close_label.is_label=true;  close_label.label = "}";
    447   out.steps.push_back(close_label);
    448 }
    449
    450 //: Make sure these pseudo recipes get consistent numbers in all tests, even
    451 //: though they aren't implemented. Allows greater flexibility in ordering
    452 //: transforms.
    453
    454 :(before "End Primitive Recipe Declarations")
    455 BREAK,
    456 BREAK_IF,
    457 BREAK_UNLESS,
    458 LOOP,
    459 LOOP_IF,
    460 LOOP_UNLESS,
    461 :(before "End Primitive Recipe Numbers")
    462 put(Recipe_ordinal, "break", BREAK);
    463 put(Recipe_ordinal, "break-if", BREAK_IF);
    464 put(Recipe_ordinal, "break-unless", BREAK_UNLESS);
    465 put(Recipe_ordinal, "loop", LOOP);
    466 put(Recipe_ordinal, "loop-if", LOOP_IF);
    467 put(Recipe_ordinal, "loop-unless", LOOP_UNLESS);
    468 :(before "End Primitive Recipe Checks")
    469 case BREAK: break;
    470 case BREAK_IF: break;
    471 case BREAK_UNLESS: break;
    472 case LOOP: break;
    473 case LOOP_IF: break;
    474 case LOOP_UNLESS: break;