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ExeDec: Execution Decomposition for Compositional Generalization in Neural Program Synthesis
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Introduces a meta-benchmark of five compositional generalization tasks for program synthesis, instantiates it on RobustFill and DeepCoder, and proposes ExeDec, a subgoal-predicting step-by-step decomposition synthesizer that outperforms Transformer baselines and improves few-shot LLM generalization.
Problem
Neural program synthesizers often fail to compositionally generalize, e.g., to longer programs or to new combinations of API concepts seen separately in training; there is no systematic benchmark for this in programming by example.
Approach
ExeDec decomposes synthesis in the execution space: a SubgoalModel predicts the next intermediate execution state for each I/O example, a SynthesizerModel generates the subprogram achieving that subgoal, and execution updates the specification in a beam search.
Key results
- On RobustFill, ExeDec achieves about +44% higher average compositional generalization than the Transformer baseline, and about +18% on DeepCoder (4.4x higher success rate per the paper's discussion).
- Compared with the no-subgoal ablation, ExeDec averages +7% on RobustFill and +5% on DeepCoder in compositional generalization.
- In few-shot PaLM 2 experiments on DeepCoder-Pythonic, the ExeDec-style prompting solves 40% to 75% more tasks than the next-best approach across settings.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| decompose synthesis into steps and predict execution subgoals before synthesizing each subprogram | Transformer program synthesizers · RobustFill compositional generalization | accuracy: +44% | Helped |
| decompose synthesis into steps and predict execution subgoals before synthesizing each subprogram | Transformer program synthesizers · DeepCoder compositional generalization | accuracy: +18% | Helped |
| add execution subgoal prediction (ablation) | no-subgoal step-by-step synthesis · RobustFill compositional generalization | accuracy: +7% | Helped |
| add execution subgoal prediction (ablation) | no-subgoal step-by-step synthesis · DeepCoder compositional generalization | accuracy: +5% | Helped |
| add execution subgoal prediction (ablation) | no-subgoal step-by-step synthesis · DeepCoder training distribution | accuracy | Hurt |
| add execution subgoal prediction (ablation) | no-subgoal step-by-step synthesis · DeepCoder length generalization | accuracy | Hurt |
| reduce model size to ExeDec-Small (ablation) | ExeDec · RobustFill and DeepCoder generalization tasks | accuracy: 1.4% worse on average and up to 3% worse on any individual generalization task | Hurt |
| increase beam size from 1 to 10 | ExeDec · RobustFill and DeepCoder | accuracy | Helped |
| use ExeDec-style prompting with execution subgoals | PaLM 2 Unicorn · DeepCoder-Pythonic, generalization average | solved tasks | Helped |
| represent DeepCoder programs in Pythonic form | ExeDec-style prompting · DeepCoder to DeepCoder-Pythonic | solved tasks | Helped |
Surprising findings
- The Transformer baseline gets the best no-generalization accuracy on DeepCoder at beam size 1 (50.7%), above ExeDec (39.1%), though ExeDec wins on generalization.
- The no-subgoal ablation is slightly better than ExeDec on DeepCoder's training distribution and on LengthGen.
Limitations
- Requires a training dataset with ground-truth line-by-line decompositions, which may not reflect natural decompositions.
- Line-by-line decomposition may not match how programmers think in larger hierarchical chunks.
- SubgoalModel predicts tokenized object values, which may not scale to complex objects.
Experimental setup
Datasets: RobustFill DeepCoder
Benchmarks: RobustFill compositional generalization splits DeepCoder compositional generalization splits DeepCoder-Pythonic
Metrics: end-to-end test accuracy solved tasks out of 200 single-step accuracy
Baselines: Transformer baseline no-subgoal ablation Latent Programmer PaLM 2 Unicorn baseline prompting Ablation-style prompting
Builds on: Latent Programmer Transformer SCAN COGS Aligned Relative Attention
Closest papers by meaning
- HYSYNTH: Context-Free LLM Approximation for Guiding Program Synthesis (NeurIPS 2024 · similarity 0.88)
- Limits of Transformer Language Models on Learning to Compose Algorithms (NeurIPS 2024 · similarity 0.86)
- Task Generalization with Autoregressive Compositional Structure: Can Learning from $D$ Tasks Generalize to $D^T$ Tasks? (ICML 2025 · similarity 0.86)
- Scaling can lead to compositional generalization (NeurIPS 2025 · similarity 0.86)
- CraftFactory: A Conditioned Control Policy Benchmark for Compositional Generalization (AAAI 2025 · similarity 0.86)
- When does compositional structure yield compositional generalization? A kernel theory. (ICLR 2025 · similarity 0.85)
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