L1: structured control flow for DVM-BASIC (fixes #100) - #101
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…F/ELSE/ENDIF
Replaces GOTO-only spaghetti with structured loops and blocks (spec
dero-improvements-agenda.md L1, P0). Halves contract size, cuts the
len(scdata)*1.5 code-size fee term, makes contracts auditable.
New dvm/control_flow.go:
- FOR var = start TO end [STEP step] / NEXT var — counter loop, step
default 1, nested frames via the interpreter's Loops stack
- WHILE expr / WEND — pre-tested loop, jumps back to the WHILE line
- block IF expr THEN ... [ELSE ...] ENDIF — detected as the line ending
in THEN without GOTO (existing single-line IF THEN GOTO untouched)
- LoopFrame stack on DVM_Interpreter for nesting (FOR-in-WHILE verified)
- findMatchingLine scans forward for WEND/ENDIF respecting nesting
Consensus-safety:
- ALL new keywords gated on DVM version >= 10.0.0 (contract must call
version("10.0.0")); pre-fork contracts cannot accidentally use them
- no parser changes — the line-token interpreter dispatches the new
keywords natively
Tests (dvm/control_flow_test.go, 8 cases):
- FOR/NEXT sum(1..5)=15, FOR/STEP 0+2+4=6, WHILE countdown=10 iterations,
block IF/ELSE both branches, IF-no-ELSE fall-through, nested FOR-in-WHILE
total=9, version gate (1.2.3 rejected), no-version gate (0.0.0 rejected)
Full dvm suite green, whole tree builds.
…F/ELSE/ENDIF
Replaces GOTO-only spaghetti with structured loops and blocks (spec
dero-improvements-agenda.md L1, P0). Halves contract size, cuts the
len(scdata)*1.5 code-size fee term, makes contracts auditable.
New dvm/control_flow.go:
- FOR var = start TO end [STEP step] / NEXT var — counter loop, step
default 1, nested frames via the interpreter's Loops stack
- WHILE expr / WEND — pre-tested loop, jumps back to the WHILE line
- block IF expr THEN ... [ELSE ...] ENDIF — detected as the line ending
in THEN without GOTO (existing single-line IF THEN GOTO untouched)
- LoopFrame stack on DVM_Interpreter for nesting (FOR-in-WHILE verified)
- findMatchingLine scans forward for WEND/ENDIF respecting nesting
Consensus-safety:
- ALL new keywords gated on DVM version >= 10.0.0 (contract must call
version("10.0.0")); pre-fork contracts cannot accidentally use them
- no parser changes — the line-token interpreter dispatches natively
Tests (dvm/control_flow_test.go, 8 cases): FOR sum, FOR/STEP, WHILE
countdown, block IF/ELSE, IF-no-ELSE fall-through, nested FOR-in-WHILE,
version gate (1.2.3), no-version gate (0.0.0). All green.
Also carries the build-manifest fix (go.mod/go.sum) for fresh-clone builds.
This was referenced Aug 23, 2026
…ndor) Same two fixes as the sibling PRs: remove the l.Operation.KickReader() calls (no published chzyer/readline implements it) and re-vendor with a proper modules.txt. Fresh-clone go build now succeeds without -mod=mod.
Author
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Superseded by PR #126 — the consolidated language package. Same code, one reviewable PR with no vendor noise. |
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Summary
L1 from the DVM-BASIC language agenda (P0): structured control flow —
FOR/NEXT,WHILE/WEND, and blockIF/ELSE/ENDIF— replacing GOTO-only spaghetti. Halves contract size (cuts thelen(scdata)*1.5code-size fee term), makes contracts auditable, and reduces GOTO bugs.The syntax
Implementation
New
dvm/control_flow.go+ aLoopFramestack onDVM_Interpreter:FOR var = start TO end [STEP step]/NEXT var— counter loop, step defaults to 1, counter lives inLocalsso it's visible to the bodyWHILE expr/WEND— pre-tested loop;WENDjumps back to theWHILEline which re-evaluatesIF expr THEN ... [ELSE ...] ENDIF— detected as anIFline ending inTHENwithoutGOTO; the existing single-lineIF expr THEN GOTO x [ELSE GOTO y]form is untouchedfindMatchingLinescans forward for the matchingWEND/ENDIFrespecting nesting (verified with FOR-in-WHILE)No parser changes — the line-token interpreter dispatches the new keywords natively.
Consensus safety
All new keywords are gated on the contract's declared DVM version (
>= 10.0.0— the contract must callversion("10.0.0")). Pre-fork contracts cannot accidentally use the new syntax; a contract at1.2.3or with noversion()call gets a clear rejection. This matches the existing intrinsic-versioning model.Tests (
dvm/control_flow_test.go, 8 cases)TestL1_ForNextFOR 1..5sums to 15TestL1_ForStepSTEP 2→ 0+2+4 = 6TestL1_WhileWendTestL1_BlockIfElseTestL1_BlockIfNoElseTestL1_NestedTestL1_VersionGateversion("1.2.3")+ FOR → rejectedTestL1_NoVersionversion()+ FOR → rejectedFull dvm suite green;
dvmpackage builds clean on the community-dev base.Relationship
>= 10.0.0, so it slots into the same HF window asverify_proof(PR feat(dvm): verify_proof PoC with executing-block roothash bind (fixes #93) #94)Branch:
feature/dvm-l1-control-flow-prin the forkliqdmetal/derohe-improvements-by-liqdmetal. Carries the build-manifest fix (go.mod/go.sum).