masm-file-structure

name	masm-file-structure
description	Enforce file structure and section ordering for Miden Assembly (.masm) files. Use when editing, reviewing, or creating .masm files.

MASM File Structure

MASM files follow a consistent top-level section order. Use section headers with the long separator line:

# SECTION NAME
# =================================================================================================

Section Order

1. Imports – use statements only; no section header
2. Type aliases – pub type / type definitions (use pub type when referenced cross-module)
3. Constants – see the masm-constants skill for organization (errors and non-error constants are grouped into separate subsections; source uses both orderings)
4. Events – const ... = event(...) definitions; appears in kernel/event-emitting modules, after Constants (or after imports when no constants section) and before the procedure sections
5. Procedures – the procedure region. Two main forms ship in v0.15 source (plus a rare variant noted below):
   • A single # PROCEDURES section holding all procedures when a module does not separate API from internals. This is a common form in source (about as many files use a lone # PROCEDURES as use the split below), e.g. standards/notes/p2id.masm, standards/data_structures/double_word_array.masm, standards/data_structures/array.masm, and shared_modules/account_id.masm. (Kernel account.masm is not this form: it uses # PROCEDURES followed by a separate # HELPER PROCEDURES section.)
   • A # PUBLIC INTERFACE section (pub proc that form the module API) followed by a # HELPER PROCEDURES section (procedures used internally, mostly non-pub)—used only when a module explicitly separates its API from its internals. Note that pub proc may still appear under # HELPER PROCEDURES when a helper is re-exported or unit-tested.

Example Structure

The module, constant, type, and procedure names below are illustrative (not a copy of any one source file); the section layout, type shapes, and import namespaces match v0.15 source.

use example::leaf::config
use example::leaf::utils
use miden::core::mem
use miden::core::word

# TYPE ALIASES
# =================================================================================================

pub type DoubleWord = struct { word_lo: word, word_hi: word }
pub type MemoryAddress = u32

# CONSTANTS
# =================================================================================================

const PROOF_DATA_PTR = 0
const CLAIM_PROOF_DATA_WORD_LEN = 134

# ERRORS
# =================================================================================================

const ERR_BRIDGE_NOT_MAINNET = "mainnet flag must be 1 for a mainnet deposit"
const ERR_LEADING_BITS_NON_ZERO = "leading bits of global index must be zero"

# PUBLIC INTERFACE
# =================================================================================================

#! Main entry point. Computes the leaf value and verifies it.
#!
#! Inputs:  [LEAF_DATA_KEY, PROOF_DATA_KEY, pad(8)]
#! Outputs: [pad(16)]
#!
#! Invocation: call
pub proc verify_leaf_root
    exec.get_leaf_value
    exec.verify_leaf
end

# HELPER PROCEDURES
# =================================================================================================

#! Loads leaf data and computes the leaf value.
#!
#! Inputs:  [LEAF_DATA_KEY]
#! Outputs: [LEAF_VALUE[8]]
#!
#! Invocation: exec
proc get_leaf_value(leaf_data_key: word) -> DoubleWord
    ...
end

#! Verifies leaf against Merkle proof.
#!
#! Inputs:  [LEAF_VALUE[8], PROOF_DATA_KEY]
#! Outputs: []
#!
#! Invocation: exec
proc verify_leaf
    ...
end

A module that does not separate its API from its internals collapses the two procedure sections into a single # PROCEDURES header instead—e.g. standards/notes/p2id.masm, whose # PROCEDURES section holds both pub proc main and pub proc new with no public/helper split.

The order of the # CONSTANTS and # ERRORS subsections is not fixed in the v0.15 source: some files place errors first (e.g. the agglayer bridge_in, bridge_config, and eth_address modules), others place non-error constants first (e.g. many miden-standards components such as signature, guardian, multisig). Both orders ship even within the same directory (standards/notes/mint.masm is constants-first while standards/notes/p2id.masm is errors-first). Either order is acceptable—just keep the two grouped separately rather than interleaved.

Type aliases are conventionally defined before constants, and v0.15 source is overwhelmingly type-first (e.g. eth_address.masm, types.masm, kernel api.masm/memory.masm). This is a convention, not an absolute: a component may place local-memory constants before a type alias—e.g. standards/data_structures/double_word_array.masm defines its SLOT_ID_PREFIX_LOC / SLOT_ID_SUFFIX_LOC / INDEX_LOC constants ahead of its in-module type DoubleWord. Prefer type-first; don't treat const-before-type as an error.

Types referenced cross-module must be marked pub type (v0.15 requires pub for any constant, procedure, or type referenced from another module). Every cross-module type alias in v0.15 source is pub type; only the in-module type DoubleWord in double_word_array.masm is non-pub. The # EVENTS subsection holds const NAME = event("...") definitions and appears in kernel/event-emitting modules. Where a constants section is present it sits after constants and before the procedure sections (e.g. the kernel account, output_note, link_map, and prologue modules); in modules with no constants section it follows the imports directly (e.g. the kernel main module and protocol/auth.masm, where # EVENTS is the first content section).

Guidelines

• Imports: One use per line; group by module/namespace. A blank line MAY separate import groups by namespace (as the kernel main/api/note/prologue/epilogue modules do), but keeping the whole block unseparated is equally common and dominant in source (e.g. the agglayer modules); the Example Structure above follows the unseparated form. Do not put a blank line between use statements within the same group. Use the bare top-level namespace, e.g. use agglayer::bridge::bridge_config and use miden::core::word—there is no miden::agglayer:: prefix. Imports normally form a single block at the top; a few source files (e.g. standards/notes/mint.masm, agglayer/bridge/bridge_out.masm) interleave a stray use near the related constants—prefer the single top block, but this is not treated as an error.
• Type aliases: Define shared types (e.g. DoubleWord, MemoryAddress) conventionally before constants. v0.15 source is overwhelmingly type-first, though a component may place local-memory constants ahead of a type alias (e.g. double_word_array.masm)—so prefer type-first but don't treat const-before-type as a violation. Mark a type pub type when it is referenced from another module (v0.15 requires pub for cross-module references); a non-pub type used only within its own module is valid.
• Constants: Defer to the masm-constants skill for organization—group non-error constants by topic and keep ERR_* in a dedicated errors subsection. The order of the errors subsection relative to the non-error constants is not fixed in source; it may come before or after, so don't treat either order as a hard rule. Just don't interleave them.
• Events: Kernel/event-emitting modules collect their const NAME = event("...") definitions in an # EVENTS subsection. It sits after the constants section when one is present, otherwise directly after the imports, and always before the procedure sections.
• Procedures: When a module does not separate its API from its internals, put every procedure under a single # PROCEDURES section (a common form in v0.15 source, e.g. standards/notes/p2id.masm, , , ). Split into and only when the module deliberately separates API from internals. (A module may also keep a header for its main procedures and add a separate section, as kernel does.)

When Sections Are Omitted

• No imports → start with type aliases or constants
• No type aliases → constants follow imports
• No events → procedure sections follow constants directly (most non-kernel modules have no # EVENTS section)
• No public/helper split → use a single # PROCEDURES section for all procedures
• No helpers → public interface is the last section

Validation Checklist

• Imports at top (if any), using the bare namespace (no miden::agglayer:: prefix)
• Type aliases before procedures; conventionally before constants (type-first is the v0.15 norm, but const-before-type is acceptable in some component files)
• Cross-module types marked pub type
• Constants before procedures; errors grouped in their own subsection, separate from non-error constants (either order)
• Events (if any) grouped in an # EVENTS subsection after constants (or after imports if no constants section) and before procedures
• Procedures under a single # PROCEDURES section, OR split into # PUBLIC INTERFACE (pub proc) before # HELPER PROCEDURES when the module separates API from internals
• Section headers use # SECTION NAME and # ===... separator