Add support for PREPARE block in stim#3409
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| mod pair_measurements; | ||
| mod pair_measurements_broadcasting; | ||
| mod preselect; | ||
| // mod prepare_block; |
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Seems like a typo comment?
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yep! Thanks for noticing, let me undo it
| self.comment(); | ||
| return self.next(); | ||
| } | ||
| self.comment(); |
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Are we getting rid of our special handling for #!... directives altogether? I thought it was a useful feature, but without the preselect, I guess we don't have any such directives we support anymore.
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We are. We decided that we'd rather bite the bullet and extend the language where needed (for example with these PREPARE blocks), but try to use the language as much as possible
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Add support for
PREPAREblocks in StimSummary
Adds a
PREPARE { ... }block to the Stim front end: a repeat-until-success region used to deterministically prepare a state that otherwise only occurs probabilistically. This replaces the previous#!preselect_*comment-annotation mechanism.How it works
PREPAREblock runs its body, then re-runs the entire block until everyREQUIREinside it is satisfied.REQUIRE rec[-1] rec[-2] ...reads measurement records (indexed backwards from the most recent measurement) and combines them by XOR (parity). If the parity is1the block restarts; if0execution continues.REQUIRE !rec[-1]), which flips that record's contribution to the parity — i.e. it requires the record to be1instead of0.prepare_N) plus a conditional branch back to it.REQUIREmay only reference records produced inside its own enclosing block; nested blocks are supported.Modifications
qir.rs— lowering forPREPARE/REQUIRE: prepare/continue labels, measurement-record resolution with scope tracking, XOR parity fold, negation (xor … , true), and new diagnostics (RequireOutsidePrepareBlock,MeasurementRecordOutOfBounds,MeasurementRecordOutOfScope).parser.rs— parsePREPAREblocks andREQUIRE; allow negation on measurement-record targets.lex.rs— drop the old#!preselect-annotation lexing.qir/tests/prepare_block.rsand parser target tests; removed the obsoleteqir/tests/preselect.rs.samples/notebooks/stim_prepare.ipynbdemonstrating preselection, negated requirements, multiple/parity requirements, and nested blocks.