Spec Update: Batch 06 — Functions

Date: 2026-04-16 Plans Referenced: Plan 035 (static methods), Plan 048 (generics), Plan 060 (closures), Plan 088 (param modes), Plan 122 (ownership), Plan 163 (pub/mut) Source Files: ast/fun.rs (Fn, Param, ParamMode, Closure), ast.rsSections Updated: Functions (Section 9) — major rewrite

Old Content

Old Functions section had 4 subsections:

• Function Definition (basic syntax)
• Function Calls
• Lambda Functions (using old |a int, b int| (int) expr syntax)
• Parameter Passing Modes (using ref/mut ref/move prefix syntax)

Issues:

• Used println() instead of print()
• Lambda syntax was wrong (used |...| instead of =>)
• Parameter modes used prefix keywords (ref, mut ref, move)
• No generic functions, no static methods, no pub visibility, no annotations

New Content

Function Definition

• Fixed to use print() instead of println()
• Noted space-separated return type (no ->)

Generic Functions (Plan 048)

• fn identity<T>(x T) T { x }
• Type constraints via has keyword

Parameter Modes (Plan 088)

• Updated to ParamMode enum: View (default), Mut, Move
• Deprecated: Copy, Take
• No more ref/mut ref prefix syntax

Static Methods (Plan 035)

• static fn new() syntax
• self keyword for instance methods

Public Visibility (Plan 163)

• pub fn, pub type, pub enum, pub spec keyword prefix

Closures (Plan 060)

• Updated to (a, b) => expr syntax (was |...|)
• Single-param: x => expr
• Capture semantics documented

Function Annotations

• #[vm], #[c], #[c, vm]

Function Kinds

• 5 kinds: Function, Lambda, Method, CFunction, VmFunction

Default Parameters

• fn greet(name str, greeting str = "Hello") str

Mutable Methods (Plan 163)

• mut fn increment() syntax

Notes

• Old lambda syntax |a, b| expr is NOT used in Auto. Use (a, b) => expr.
• self is implicit in methods (no need to declare as parameter)
• FnKind::VmFunction is for functions implemented via VM registry, not declared by users