Slop

Standard library modules:

Tooling

SLOP is self-hosted: native compiler binaries are used by default. Use --python on most commands to fall back to the Python toolchain.

# Inspection and documentation
slop parse file.slop              # Parse and inspect AST
slop parse file.slop --holes      # Show holes in file
slop doc file.slop                # Generate documentation from annotations
slop ref                          # Full language reference (for AI)
slop ref types                    # Type system reference
slop ref --list                   # List available topics
slop paths                        # Show resolved SLOP paths

# Verification
slop check file.slop              # Type check
slop verify file.slop             # Verify contracts with Z3
slop verify file.slop --mode warn # Warn instead of error on failures
slop test file.slop               # Run @example and @property tests

# Building
slop transpile file.slop -o out.c # Transpile to C
slop build file.slop -o binary    # Full build (requires cc)
slop build file.slop --library static  # Build as static library
slop build file.slop --skip-check     # Skip type checking

# Code generation and formatting
slop fill file.slop -o filled.slop  # Fill holes with LLM
slop derive schema.json -o types.slop  # Generate types from schema
slop format file.slop               # Format SLOP source code
slop format file.slop --check       # Check formatting (CI)

Philosophy

Humans: Specify WHAT (intent, contracts, types, examples)
Machines: Handle HOW (implementation, verification, compilation)
Type system: Catch errors early (range bounds, exhaustive matching, contract violations)

SLOP PAREDIT MODE

When generating or editing SLOP code, follow these structural editing rules to ensure syntactically correct output.

Rules

1. Balanced parentheses - ALL code must have perfectly balanced ( and ). Count obsessively.

2. Structural editing terminology - Describe changes using structural operations BEFORE showing code:

   • slurp: Expand sexp to include next sibling
   • barf: Expel last child from sexp
   • splice: Remove surrounding parens, keeping children
   • raise: Replace parent with this sexp
   • wrap: Surround expression with new parens
   • unwrap: Remove one level of parens
   • kill-sexp: Delete entire balanced expression

3. <slop-paren-audit> requirement - Before ANY SLOP code block, insert an audit:

   <slop-paren-audit>
   Line 1: ( = 3, ) = 3
   Line 2: ( = 2, ) = 2
   Total: ( = 5, ) = 5 ✓
   </slop-paren-audit>
   

4. BEFORE/AFTER structure - When editing existing code, show markers:

   BEFORE: →( target-sexp )←
   AFTER:  →( new-sexp )←
   

5. Atomic units - Treat these as indivisible:

   • @-forms: (@intent ...), (@spec ...), (@pre ...), etc.
   • (hole ...) expressions
   • (fn ...), (type ...), (module ...), (ffi ...) declarations

6. Infix {} as unit - Treat entire {infix conditions} as one balanced sexp unit:

   (@pre {x > 0 and x < 100})  ; {} is atomic
   

7. Refuse risky edits - If a requested edit risks breaking structure, refuse and suggest the structural equivalent. Never produce unbalanced code.

8. SLOP idioms:

   • Keep @-contracts together at top of function body
   • Indent generously (2 spaces per level)
   • Align let bindings vertically
   • One form per line for readability

Quick Reference

Syntax

; Comment
;; Documentation comment
(module name (export ...) forms...)
(import module-name name*)
(type Name type-expr)
(const NAME Type const-expr)
(fn name ((param Type)...) annotations... body)
(fn name ((param Type)...) annotations... body :c-name "c_name") ; C name override
(fn ((param Type)...) body)           ; Lambda (anonymous function)

Constants

(const NAME Type const-expr)

;; const-expr: literals, other constants, arithmetic/bitwise, sizeof
;; NOT allowed: function calls, variables, runtime expressions

(const MAX_CONN Int 128)
(const BUF_SIZE U64 (* 4 1024))
(const FLAGS Int (| FLAG_A FLAG_B))

C Mapping: integers → #define, others → static const.

Parameter Modes

(fn name ((in x Type)        ; Read-only (default) - pass by value
          (out result Type)  ; Write-only - pointer to uninitialized
          (mut state Type))  ; Mutable - value or pointer depending on Type
  ...)

Variables and Mutability

;; Immutable bindings (default) - set! is NOT allowed
(let ((x 10)
      (y 20))
  (+ x y))

;; Sequential bindings - later bindings can reference earlier ones
(let* ((x 10)
       (y (+ x 5)))    ; y can use x
  (+ x y))             ; → 25

;; Mutable bindings - set! IS allowed
(let ((mut counter 0))
  (set! counter (+ counter 1))
  counter)

;; Mutable with explicit type
(let ((mut total Int 0))
  (for (i 0 10)
    (set! total (+ total i)))
  total)

Important: set! on a variable requires the mut keyword in its binding.

Types with Ranges

(Int)                  ; Any integer (int64_t)
(Int 0 ..)             ; Non-negative
(Int 1 .. 100)         ; Bounded range
(I8) (I16) (I32) (I64) ; Explicit width signed
(U8) (U16) (U32) (U64) ; Explicit width unsigned
(Float)                ; 64-bit float (double)
(F32)                  ; 32-bit float
(Bool)                 ; true or false
(String)               ; Record: { data: (Ptr U8), len: U64 }
(String 1 .. 255)      ; Length-bounded string
(Bytes)                ; Record: { data: (Ptr U8), len: U64, cap: U64 }
(List T 1 ..)          ; Non-empty list
(Array T 10)           ; Fixed-size array (stack allocated)
(Slice T)              ; View into array/list
(Ptr T)                ; Pointer to T
(ScopedPtr T)          ; Scoped pointer (freed when scope ends)
(OptPtr T)             ; Nullable pointer
(Option T)             ; T or none
(Result T E)           ; Success or error
(Map K V)              ; Hash map
(Set T)                ; Hash set
(Chan T)               ; Typed channel (concurrency)
(Thread T)             ; Thread handle returning T
(enum a b c)           ; Enumeration
(record (x T) (y U))   ; Struct
(union (a T) (b U))    ; Tagged union

;; Collection literals - IMMUTABLE values
(list Int 1 2 3)                ; Immutable list with explicit type
(list 1 2 3)                    ; Inferred from first element
(map String Int ("a" 1) ("b" 2)) ; Immutable map with explicit types
(map ("a" 1) ("b" 2))           ; Inferred from first pair

;; For mutable collections, use list-new/map-new with mut binding:
(let ((mut items (list-new arena Int)))
  (list-push items 1)           ; OK: items is mutable
  items)

;; See references/types.md for complete type reference

Generic Functions

(@generic (T))                   ; Single type parameter
(@generic (T U))                 ; Multiple type parameters

;; Type variables appear in @spec param/return types
(fn identity ((in x T))
  (@generic (T))
  (@intent "Return the value unchanged")
  (@spec ((T) -> T))
  (@pure)
  x)

At call sites, the type checker unifies argument types to bind type variables and substitutes into the return type.

Required Annotations

(fn name ((params...))
  (@intent "Human-readable purpose")     ; REQUIRED
  (@spec ((ParamTypes) -> ReturnType))   ; REQUIRED
  body)

Contracts (For Verification)

Contracts enable automated testing and future SMT verification. Always specify when possible - they are essential to SLOP's verification story.

(@pre condition)           ; Precondition - REQUIRED for non-trivial functions
(@post condition)          ; Postcondition ($result = return value)
(@assume condition)        ; Trusted axiom for verification (e.g., FFI behavior)
(@pure)                    ; No side effects, deterministic
(@trusted)                 ; Skip verification entirely (for unverifiable functions)
(@doc "Extended documentation")  ; Detailed docs, emits as C comment
(@example (args) -> result) ; Executable test case - include multiple!
(@example :eq eq-fn (args) -> result) ; Test with custom equality function
(@alloc arena)             ; Function allocates in arena
(@alloc static)            ; Returns static/global data
(@alloc none)              ; Does not allocate

Infix Notation for Contracts (Preferred)

Contracts support infix notation using curly braces. Prefer infix for scaffolds as it's more readable:

;; Infix notation - PREFERRED for scaffolds
(@pre {x > 0})
(@pre {x >= 0 and x <= 100})
(@post {$result == a + b})

;; Prefix notation (also valid)
(@pre (> x 0))
(@post (== $result (+ a b)))

Infix precedence (high to low): *, /, % → +, - → comparisons → and → or

Grouping and function calls:

(@pre {(a + b) * c > 0})           ; Use () for grouping
(@pre {(len arr) > 0})             ; Use prefix for function calls
(@post {$result >= (min a b)})     ; Mix infix operators with prefix calls

Examples are especially important - they serve as:

• Documentation by example
• Test cases for automated testing
• Guidance for hole filling

Advanced Annotations

(@property (forall (x T) expr))   ; Property assertion
(@deprecated "message")           ; Deprecation notice
(@generation-mode mode)           ; deterministic|template|llm
(@derived-from "path")            ; Source tracking
(@generated-by src :version v)    ; Generation metadata
(@requires category :prompt "..." (fn-sigs...))  ; Requirements
(@loop-invariant condition)       ; Loop invariant (verification escape hatch)
(@invariant condition)            ; Type invariant (on type definitions)
(@callback-assume param expr)    ; Property of callback args ($callback-arg for each arg)

Type Invariants

Use @invariant on type definitions to specify relational constraints between fields. Invariant expressions use field names directly (not prefixed):

(type Graph (record (triples (List Triple)) (size GraphSize))
  (@invariant (== size (list-len triples))))

(type Counter (record (count (Int 0 ..)) (max-count (Int 1 ..)))
  (@invariant (<= count max-count)))

Loop Invariants

Use @loop-invariant inside loops for verification:

(let ((mut sum 0))
  (for (i 0 n)
    (@loop-invariant {sum >= 0})
    (set! sum (+ sum i)))
  sum)

Callback Assumptions

Use @callback-assume to declare properties of callback arguments in higher-order functions:

(fn for-each-item ((g Graph) (callback (Fn (Item) Unit)))
  (@intent "Apply callback to each item in graph")
  (@spec ((Graph (Fn (Item) Unit)) -> Unit))
  (@callback-assume callback (graph-contains g $callback-arg))
  ...)
;; $callback-arg refers to each argument passed to the callback

The verifier desugars callback-taking function calls into for-each loops and transforms @callback-assume into (forall (t $result) ...) axioms for Z3 reasoning.

Requirements (Scaffold Dependencies)

The @requires annotation declares dependencies that must be provided before code can be filled:

(@requires storage
  :prompt "Which storage approach?"
  :options (
    ("In-memory Map" map)
    ("Database via FFI" db))
  ;; Required function signatures
  (state-get-pet ((state (Ptr State)) (id PetId)) -> (Option (Ptr Pet)))
  (state-insert-pet ((state (Ptr State)) (pet (Ptr NewPet))) -> Pet))

Memory Model

;; Arena allocation (primary pattern)
(with-arena 4096
  (let ((data (arena-alloc arena (sizeof Data))))
    ...))  ; Arena freed at end

;; Named arenas (binds custom name instead of 'arena')
(with-arena :as scratch 4096
  (arena-alloc scratch 256))  ; Uses 'scratch' instead of 'arena'

;; Nested named arenas for different lifetimes
(with-arena :as output 8192
  (with-arena :as scratch 4096
    (let ((temp (parse scratch input)))
      (build-result output temp))))
;; scratch freed first, then output

;; For allocating functions, pass arena as first param
(fn create-user ((arena Arena) (name String))
  (@alloc arena)
  ...)

;; Mutable pointer for in-place modification
(let ((mut conn (create-connection arena)))
  (set! conn state 'connected)
  conn)

;; Slices (borrowed views)
(fn process ((data (Slice U8)))
  (for-each (byte data) ...))

Holes (For LLM Generation)

Two modes: generation (create new code) and refactoring (improve existing code).

;; Generation mode - create new implementation
(hole Type "prompt")
(hole Type "prompt"
  :complexity tier-2          ; tier-1 to tier-4
  :context (var1 var2 fn1)    ; Whitelist of available identifiers
  :required (var1 fn1)        ; Identifiers that must appear in output
  :examples ((in) -> out))

;; Refactoring mode - improve existing code
;; Pass existing code as the 3rd positional argument (after Type and prompt)
(hole Type "prompt"
  existing-code-expression    ; The code to refactor/improve
  :complexity tier-3)

;; Example: Refactor for performance
(hole Int "optimize this loop"
  (let ((mut sum 0))
    (for (i 0 n)
      (set! sum (+ sum (* i i))))
    sum)
  :complexity tier-3
  :context (n))

Complexity Tiers:

• tier-1: 1-3B models (trivial: simple arithmetic, field access)
• tier-2: 7-8B models (simple conditionals, result construction)
• tier-3: 13-34B models (loops, multiple conditions, state)
• tier-4: 70B+ models (algorithms, complex state machines)

Pattern Syntax

;; In match expressions:
_                           ; Wildcard
identifier                  ; Binding (captures value)
'symbol                     ; Quoted value (enum variant match)
literal                     ; Literal match
(array p1 p2...)           ; Array pattern
(list p1 p2... | rest)     ; List with rest
(record Type (f1 p1)...)   ; Struct destructure
(union Tag pattern)        ; Union variant
(guard pattern when expr)  ; Guarded pattern

Important: Use quoted symbols 'Fizz for enum value matches. Bare identifiers are bindings.

Common Patterns

;; Error handling (Result type)
(match (might-fail x)
  ((ok val) (use val))
  ((error e) (handle e)))

;; Simple enum matching - bare variant names
(match status
  (Active (do-active))
  (Inactive (do-inactive)))

;; Field access (auto -> for pointers)
(. record field)           ; record.field or record->field
(set! record field value)  ; Mutation
(@ array index)            ; Array indexing

;; Loops
(for (i 0 10) body)
(for-each (x collection) body)       ; Iterate List, Set, or Map (keys only)
(for-each ((key value) map) body)    ; Iterate Map key-value pairs
(while cond body)
(break) (continue) (return expr)

;; for-each collection types:
;; - List: elements in order
;; - Set: elements (order undefined)
;; - Map with (var map): iterates keys only
;; - Map with ((k v) map): iterates key-value pairs

;; Data construction
(record-new Type (f1 v1) (f2 v2))  ; Named fields
(TypeName v1 v2 ...)               ; Positional (order matches definition)
(union-new Type Tag value)
(ok val) (error 'variant)  ; QUOTE the error variant!
(some val) (none)

;; Address-of and dereference
(addr expr)                ; &expr
(deref ptr)                ; *ptr

;; Error handling shorthand
(? fallible-expr)          ; Early return on error

FFI (Foreign Function Interface)

;; Declare C functions and constants
(ffi "header.h"
  (func-name ((param Type)...) ReturnType)  ; Function
  (func-name ((param Type)...) ReturnType :variadic) ; Variadic function
  (CONST_NAME Type)                          ; Constant (no params = constant)
  ...)

;; Declare C structs for field access
(ffi-struct "header.h" struct_name
  (field1 Type1)
  (field2 Type2))

;; When SLOP name differs from C name
(ffi-struct "sys/stat.h" stat_buf :c-name "stat"
  (st_size I64)
  (st_mode U32))

;; Type casting
(cast Type expr)

;; C inline escape hatch
(c-inline "SOME_C_CONSTANT")

;; FFI-only type: Char
;; Use Char for C char* parameters (distinct from I8/U8)
(ffi "string.h"
  (strcpy ((dest (Ptr Char)) (src (Ptr Char))) (Ptr Char)))

Example:

(ffi "stdio.h"
  (SEEK_SET Int)                             ; Constant
  (SEEK_CUR Int)
  (EOF Int)
  (printf ((fmt (Ptr Char))) Int :variadic)  ; Variadic C function
  (fclose ((file (Ptr Void))) Int))          ; Function

(ffi "unistd.h"
  (read ((fd Int) (buf (Ptr U8)) (n U64)) I64)
  (write ((fd Int) (buf (Ptr U8)) (n U64)) I64)
  (close ((fd Int)) Int))

(ffi-struct "netinet/in.h" sockaddr_in
  (sin_family U16)
  (sin_port U16)
  (sin_addr U32))

C Mapping

SLOP                    C
────                    ─
(Int 0 .. 255)     →    uint8_t + range check
(Ptr User)         →    User*
(. user name)      →    user->name (auto-detects pointer)
(arena-alloc ...)  →    slop_arena_alloc(...)
(@pre {x > 0})     →    SLOP_PRE(x > 0, "x > 0")
(@post {$result > 0}) → SLOP_POST(result > 0, "result > 0")

Standard Library

;; Arithmetic
(+ a b) (- a b) (* a b) (/ a b) (% a b)
(min a b) (max a b)      ; Minimum/maximum of two values

;; Memory
(arena-new size) (arena-alloc arena size) (arena-free arena)
(with-arena size body)              ; Scoped arena, implicit 'arena' var
(with-arena :as name size body)     ; Named scoped arena, binds 'name'
(sizeof Type) (addr expr) (deref ptr)

;; I/O (String, Int, Bool, or Float - type inferred)
(print val) (println val)

;; Strings (builtins)
(int-to-string arena n)  ; Int -> String
(string-new arena str) (string-len s) (string-concat arena a b)
(string-eq a b) (string-slice s start end) (string-split arena s delim)
(string-push-char arena s c)  ; Append U8 char to string

;; Strings (strlib - requires import)
;; (import strlib (starts-with ends-with contains trim parse-int float-to-string))
;; float-to-string: (float-to-string arena f) ; Float -> String

;; Lists
(list-new arena Type)           ; Create empty mutable list
(list Type e1 e2...)            ; Immutable literal
(list-push list item)           ; Mutates list (requires mut binding)
(list-pop list)                 ; Remove and return last element -> (Option T)
(list-get list idx) (list-len list)

;; Maps
(map-new arena KeyType ValType) ; Create empty mutable map
(map KeyType ValType (k1 v1)...)  ; Immutable literal
(map-put m k v)                 ; Mutates map (requires mut binding)
(map-get m k) (map-has m k)
(map-keys m)                    ; Return list of all keys
(map-remove m k)                ; Remove key from mutable map

;; Sets
(set-new arena ElementType)     ; Create empty mutable set
(set Type e1 e2...)             ; Immutable set literal
(set-put set elem)              ; Add element to set
(set-has set elem)              ; Check if element exists -> Bool
(set-remove set elem)           ; Remove element from set
(set-elements set)              ; Get all elements as list

;; Result
(ok val) (error 'variant) (is-ok r) (unwrap r)

;; Option
(some val) (none) (is-some o) (is-none o)

;; Time
(now-ms) (sleep-ms ms)

;; Concurrency (thread library)
(chan Type arena)            ; Create unbuffered channel → (Ptr (Chan T))
(chan-buffered Type arena cap) ; Create buffered channel → (Ptr (Chan T))
(chan-close ch)             ; Close channel
(send ch value)             ; Send value (blocks if full) → (Result Unit ChanError)
(recv ch)                   ; Receive value (blocks if empty) → (Result T ChanError)
(try-recv ch)               ; Non-blocking receive → (Result T ChanError)
(spawn arena func)          ; Spawn thread running func → (Ptr (Thread T))
(join thread)               ; Wait for thread, get result

Generation Guidelines

1. Always include @intent and @spec
2. Use @pre/@post to specify contracts for all non-trivial functions
3. Prefer infix notation for contracts: (@pre {x > 0}) not (@pre (> x 0))
4. Include @example annotations - at least 2-3 per function
5. Mark pure functions with @pure for optimization and testing
6. Use range types to constrain values
7. Pass Arena as first param for allocating functions
8. Use (Result T E) for fallible operations
9. Mark hole complexity for optimal model routing
10. Quote error variants: (error 'not-found) not (error not-found)
11. Use mut for mutable bindings: (let ((mut x 0)) (set! x 1))
12. Use list-new/map-new with mut binding for mutable collections

Scaffold Generation Guidelines

When generating SLOP scaffolds (files with holes for LLM filling):

Use Named Types Consistently

;; GOOD: Use the named type in signatures
(type PetId (Int 1 ..))
(fn get-pet ((id PetId)) ...)

;; BAD: Inline range (LLM won't connect it to PetId)
(fn get-pet ((id (Int 1 ..))) ...)

Variant Names Must Be Globally Unique

Compile-time requirement: Variant names must be globally unique across all enum and union types in a module. Using the same variant name in different types will result in a compile error.

;; COMPILE ERROR: 'bad-request' and 'not-found' used in multiple types
(type ApiError (enum bad-request not-found))
(type HttpStatus (enum ok bad-request not-found))

;; CORRECT: Unique variant names across all types
(type ApiError (enum api-bad-request api-not-found))
(type HttpStatus (enum http-ok http-bad-request http-not-found))

Quote Enum Variants in Code

;; GOOD
(error 'not-found)

;; BAD - "Undefined variable: not-found"
(error not-found)

Match Constant Types to Usage

;; If function expects (Int 0 ..):
(const HANDLER_ID Int 0)        ;; BAD - type mismatch
(const HANDLER_ID (Int 0 ..) 0) ;; GOOD

Use :context for Available Scope, :required for Mandates

;; :context = whitelist of what CAN be used
;; :required = what MUST appear in output

(hole Unit "delete"
  :context (state id)          ; Can use these
  :required (state-delete-pet)) ; Must call this

Module Names Must Match Filenames

;; File: petstore.slop
(module petstore ...)  ;; GOOD

;; File: petstore-api.slop
(module petstore ...)  ;; BAD - resolver won't find it

Verification Levels

SLOP provides multiple levels of verification:

1. Parse-time: S-expression well-formed
2. Generation-time: LLM self-check against constraints
3. Compile-time: Type checking, range analysis, contract consistency, exhaustiveness
4. Test-time: @example execution, @property testing
5. Runtime (debug): Assertion checks, bounds checking

Validation

After generating SLOP files, run the type checker:

slop check path/to/file.slop

Expected behavior with holes:

• Files with unfilled holes will show UnfilledHoleError - expected for scaffolds
• All other errors (type errors, syntax errors, undefined references) should be fixed

CLI Commands

Installation

pip install -e .

Parsing and Inspection

slop parse file.slop              # Parse and inspect
slop parse file.slop --holes      # Show holes in file

Type Checking

slop check file.slop              # Type check a file

Contract Verification

slop verify file.slop             # Verify contracts with Z3 (requires z3-solver)
slop verify file.slop --mode warn # Warn instead of error
slop verify file.slop --timeout 10 # Set Z3 timeout (seconds)

The verifier checks:

• @pre and @post contract consistency (path-sensitive)
• Range type bounds propagation through arithmetic
• Type invariants (@invariant)
• Record field axioms and union tag axioms
• Imported function postcondition propagation
• Six automatic loop patterns (filter, map/transform, count, fold, find-first, nested/join)
• @property auto-propagation as loop invariants
• @callback-assume for higher-order function reasoning
• list-contains verifier-only predicate (usable in annotations, no runtime representation)

Verifier-only predicates:

• (list-contains lst elem) — membership test for @post, @property, @loop-invariant, @assume annotations only (no C codegen)

See $SLOP_HOME/spec/VERIFICATION.md for the full verification guide.

Hole Validation

# Validate a hole implementation against expected type
slop check-hole '(+ x 1)' -t Int -p '((x Int))'

# With context from a file
slop check-hole '(helper 42)' -t Int -c myfile.slop

# From stdin
echo '(ok value)' | slop check-hole -t '(Result T E)'

Transpilation and Building

slop transpile file.slop -o output.c   # Transpile to C
slop build file.slop -o binary         # Full build (requires cc)
slop build file.slop --library static  # Build as static library
slop build file.slop --library shared  # Build as shared library
slop build file.slop --skip-check      # Skip type checking (bootstrapping)

Build Modes:

• Debug: -g -DSLOP_DEBUG - runtime contract checks enabled
• Release: -O3 -DNDEBUG - contract checks removed for speed
• Safe: -O2 -DSLOP_SAFE - contract checks with optimization

Most commands accept --python to use the Python toolchain instead of native binaries.

Other Commands

slop derive schema.json -o types.slop  # Generate types from schema
slop fill file.slop -o filled.slop     # Fill holes with LLM
slop test file.slop                    # Run @example and @property tests
slop test file.slop --rebuild          # Rebuild before testing
slop format file.slop                  # Format SLOP source code
slop format file.slop --check          # Check formatting (exit 1 if not)
slop paths                             # Show resolved SLOP paths
slop paths -v                          # Verbose (show examples list)

Documentation Generation

slop doc file.slop                     # Generate markdown docs to stdout
slop doc file.slop -o docs.md          # Write to file
slop doc file.slop -f json             # Output as JSON

Extracts @intent, @spec, @pre, @post, @example annotations into readable documentation.

Language Reference (for AI)

slop ref                  # Full language reference
slop ref types            # Type system reference
slop ref --list           # List available topics

Use slop ref for quick lookups of syntax, built-ins, and patterns.

Common Mistakes

These functions/patterns do NOT exist in SLOP - use the alternatives:

Module Structure

All definitions must be INSIDE the module form:

;; CORRECT:
(module my-module
  (export public-fn)

  (type MyType (Int 0 ..))

  (fn public-fn (...)
    ...))  ; <-- closing paren wraps entire module

;; WRONG:
(module my-module
  (export public-fn))

(fn public-fn ...)  ; ERROR: outside module form

Error Returns

Quote error variants:

(error 'not-found)     ; CORRECT: quoted
(error not-found)      ; WRONG: undefined variable

See Also

• references/types.md - Full type system
• references/patterns.md - Common patterns
• references/common-mistakes.md - What NOT to do