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#618 alternative to dupn #2059

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#618 alternative to dupn #2059

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a6370e5
#618 simplify foreach - get rid of the FORK and DUPN
leonid-s-usov Feb 10, 2020
145848f
#618 POC refactor reduce - get rid of DUPN by emulating a FORK1
leonid-s-usov Feb 11, 2020
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38 changes: 15 additions & 23 deletions src/compile.c
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Original file line number Diff line number Diff line change
Expand Up @@ -830,8 +830,9 @@ static block bind_alternation_matchers(block matchers, block body) {
}

block gen_reduce(block source, block matcher, block init, block body) {
block res_var = gen_op_var_fresh(STOREV, "reduce");
block loop = BLOCK(gen_op_simple(DUPN),
block res_var = gen_op_var_fresh(STOREV, "*reduce");
block dot_var = gen_op_var_fresh(STOREV, "*dot");
block loop = BLOCK(gen_op_simple(DUP),
source,
bind_alternation_matchers(matcher,
BLOCK(gen_op_bound(LOADVN, res_var),
Expand All @@ -841,15 +842,23 @@ block gen_reduce(block source, block matcher, block init, block body) {
return BLOCK(gen_op_simple(DUP),
init,
res_var,
BLOCK(
// dummy null
gen_op_pushk_under(jv_null()),
// stores the actual input
dot_var
),
gen_op_target(FORK, loop),
//consumes dummy null and null-restores the actual input
gen_op_bound(LOADVN, dot_var),
loop,
//consumes dummy null and null-restores the result
gen_op_bound(LOADVN, res_var));
}

block gen_foreach(block source, block matcher, block init, block update, block extract) {
block output = gen_op_targetlater(JUMP);
block state_var = gen_op_var_fresh(STOREV, "foreach");
block loop = BLOCK(gen_op_simple(DUPN),
block loop = BLOCK(gen_op_simple(DUP),
// get a value from the source expression:
source,
// destructure the value into variable(s) for all the code
Expand All @@ -864,28 +873,11 @@ block gen_foreach(block source, block matcher, block init, block update, block e
// save new state
gen_op_bound(STOREV, state_var),
// extract an output...
extract,
// ...and output it by jumping
// past the BACKTRACK that comes
// right after the loop body,
// which in turn is there
// because...
//
// (Incidentally, extract can also
// backtrack, e.g., if it calls
// empty, in which case we don't
// get here.)
output)));
extract)));
block foreach = BLOCK(gen_op_simple(DUP),
init,
state_var,
gen_op_target(FORK, loop),
loop,
// ...at this point `foreach`'s original input
// will be on top of the stack, and we don't
// want to output it, so we backtrack.
gen_op_simple(BACKTRACK));
inst_set_target(output, foreach); // make that JUMP go bast the BACKTRACK at the end of the loop
loop);
return foreach;
}

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