https://github.com/akkartik/mu/blob/master/028call_return.cc

      1 //: Calls can also generate products, using 'reply' or 'return'.
      2
      3 :(scenario return)
      4 def main [
      5   1:num, 2:num <- f 34
      6 ]
      7 def f [
      8   12:num <- next-ingredient
      9   13:num <- add 1, 12:num
     10   return 12:num, 13:num
     11 ]
     12 +mem: storing 34 in location 1
     13 +mem: storing 35 in location 2
     14
     15 :(scenario reply)
     16 def main [
     17   1:num, 2:num <- f 34
     18 ]
     19 def f [
     20   12:num <- next-ingredient
     21   13:num <- add 1, 12:num
     22   reply 12:num, 13:num
     23 ]
     24 +mem: storing 34 in location 1
     25 +mem: storing 35 in location 2
     26
     27 :(before "End Primitive Recipe Declarations")
     28 RETURN,
     29 :(before "End Primitive Recipe Numbers")
     30 put(Recipe_ordinal, "return", RETURN);
     31 put(Recipe_ordinal, "reply", RETURN);  // synonym while teaching
     32 put(Recipe_ordinal, "output", RETURN);  // experiment
     33 :(before "End Primitive Recipe Checks")
     34 case RETURN: {
     35   break;  // checks will be performed by a transform below
     36 }
     37 :(before "End Primitive Recipe Implementations")
     38 case RETURN: {
     39   // Begin Return
     40   if (Trace_stream) {
     41     trace("trace") << current_instruction().name << ": decrementing callstack depth from " << Trace_stream->callstack_depth << end();
     42     --Trace_stream->callstack_depth;
     43     if (Trace_stream->callstack_depth < 0) {
     44       Current_routine->calls.clear();
     45       goto stop_running_current_routine;
     46     }
     47   }
     48   Current_routine->calls.pop_front();
     49   // just in case 'main' returns a value, drop it for now
     50   if (Current_routine->calls.empty()) goto stop_running_current_routine;
     51   for (int i = 0;  i < SIZE(ingredients);  ++i)
     52     trace(9998, "run") << "result " << i << " is " << to_string(ingredients.at(i)) << end();
     53   // make return products available to caller
     54   copy(ingredients.begin(), ingredients.end(), inserter(products, products.begin()));
     55   // End Return
     56   break;  // continue to process rest of *caller* instruction
     57 }
     58
     59 //: Types in return instructions are checked ahead of time.
     60
     61 :(before "End Checks")
     62 Transform.push_back(check_types_of_return_instructions);  // idempotent
     63 :(code)
     64 void check_types_of_return_instructions(const recipe_ordinal r) {
     65   const recipe& caller = get(Recipe, r);
     66   trace(9991, "transform") << "--- check types of return instructions in recipe " << caller.name << end();
     67   for (int i = 0;  i < SIZE(caller.steps);  ++i) {
     68     const instruction& caller_instruction = caller.steps.at(i);
     69     if (caller_instruction.is_label) continue;
     70     if (caller_instruction.products.empty()) continue;
     71     if (is_primitive(caller_instruction.operation)) continue;
     72     const recipe& callee = get(Recipe, caller_instruction.operation);
     73     for (int i = 0;  i < SIZE(callee.steps);  ++i) {
     74       const instruction& return_inst = callee.steps.at(i);
     75       if (return_inst.operation != RETURN) continue;
     76       // check types with the caller
     77       if (SIZE(caller_instruction.products) > SIZE(return_inst.ingredients)) {
     78         raise << maybe(caller.name) << "too few values returned from " << callee.name << '\n' << end();
     79         break;
     80       }
     81       for (int i = 0;  i < SIZE(caller_instruction.products);  ++i) {
     82         reagent/*copy*/ lhs = return_inst.ingredients.at(i);
     83         reagent/*copy*/ rhs = caller_instruction.products.at(i);
     84         // End Check RETURN Copy(lhs, rhs)
     85         if (!types_coercible(rhs, lhs)) {
     86           raise << maybe(callee.name) << return_inst.name << " ingredient '" << lhs.original_string << "' can't be saved in '" << rhs.original_string << "'\n" << end();
     87           raise << "  ['" << to_string(lhs.type) << "' vs '" << to_string(rhs.type) << "']\n" << end();
     88           goto finish_return_check;
     89         }
     90       }
     91       // check that any return ingredients with /same-as-ingredient connect up
     92       // the corresponding ingredient and product in the caller.
     93       for (int i = 0;  i < SIZE(caller_instruction.products);  ++i) {
     94         if (has_property(return_inst.ingredients.at(i), "same-as-ingredient")) {
     95           string_tree* tmp = property(return_inst.ingredients.at(i), "same-as-ingredient");
     96           if (!tmp || !tmp->atom) {
     97             raise << maybe(caller.name) << "'same-as-ingredient' metadata should take exactly one value in '" << to_original_string(return_inst) << "'\n" << end();
     98             goto finish_return_check;
     99           }
    100           int ingredient_index = to_integer(tmp->value);
    101           if (ingredient_index >= SIZE(caller_instruction.ingredients)) {
    102             raise << maybe(caller.name) << "too few ingredients in '" << to_original_string(caller_instruction) << "'\n" << end();
    103             goto finish_return_check;
    104           }
    105           if (!is_dummy(caller_instruction.products.at(i)) && !is_literal(caller_instruction.ingredients.at(ingredient_index)) && caller_instruction.products.at(i).name != caller_instruction.ingredients.at(ingredient_index).name) {
    106             raise << maybe(caller.name) << "'" << to_original_string(caller_instruction) << "' should write to '" << caller_instruction.ingredients.at(ingredient_index).original_string << "' rather than '" << caller_instruction.products.at(i).original_string << "'\n" << end();
    107           }
    108         }
    109       }
    110       finish_return_check:;
    111     }
    112   }
    113 }
    114
    115 bool is_primitive(recipe_ordinal r) {
    116   return r < MAX_PRIMITIVE_RECIPES;
    117 }
    118
    119 :(scenario return_type_mismatch)
    120 % Hide_errors = true;
    121 def main [
    122   3:num <- f 2
    123 ]
    124 def f [
    125   12:num <- next-ingredient
    126   13:num <- copy 35
    127   14:point <- copy 12:point/raw
    128   return 14:point
    129 ]
    130 +error: f: return ingredient '14:point' can't be saved in '3:num'
    131
    132 //: In Mu we'd like to assume that any instruction doesn't modify its
    133 //: ingredients unless they're also products. The /same-as-ingredient inside
    134 //: the recipe's 'return' indicates that an ingredient is intended to be
    135 //: modified in place, and will help catch accidental misuse of such
    136 //: 'ingredient-products' (sometimes called in-out parameters in other
    137 //: languages).
    138
    139 :(scenario return_same_as_ingredient)
    140 % Hide_errors = true;
    141 def main [
    142   1:num <- copy 0
    143   2:num <- test1 1:num  # call with different ingredient and product
    144 ]
    145 def test1 [
    146   10:num <- next-ingredient
    147   return 10:num/same-as-ingredient:0
    148 ]
    149 +error: main: '2:num <- test1 1:num' should write to '1:num' rather than '2:num'
    150
    151 :(scenario return_same_as_ingredient_dummy)
    152 def main [
    153   1:num <- copy 0
    154   _ <- test1 1:num  # call with different ingredient and product
    155 ]
    156 def test1 [
    157   10:num <- next-ingredient
    158   return 10:num/same-as-ingredient:0
    159 ]
    160 $error: 0
    161
    162 :(code)
    163 string to_string(const vector<double>& in) {
    164   if (in.empty()) return "[]";
    165   ostringstream out;
    166   if (SIZE(in) == 1) {
    167     out << no_scientific(in.at(0));
    168     return out.str();
    169   }
    170   out << "[";
    171   for (int i = 0;  i < SIZE(in);  ++i) {
    172     if (i > 0) out << ", ";
    173     out << no_scientific(in.at(i));
    174   }
    175   out << "]";
    176   return out.str();
    177 }