Add first-class function literals: function(params) expr (v3.6)

[particlesector]

Summary

Closes the largest gap explicitly deferred by the v3.5 completeness audit (docs/roadmap.md): first-class function literals, OpenSCAD 2019.05+.

• f = function(x) x*2; now evaluates to a real closure Value (AST pointer + captured defining scope) that can be assigned to a variable, stored in a list, passed as an argument to (or returned from) another function, and invoked later via ordinary f(...) call syntax wherever f names a variable holding one.
• Lexical scoping: a closure sees the variables visible where function(...) ... was written, not the scope it's called from.
• Direct self-recursion: fact = function(n) n<=1 ? 1 : n*fact(n-1); recurses by name without needing a named function def — implemented narrowly (only when the literal is directly on the assignment's right-hand side) so a plain copy like g = f; can't leak g into f's own captured scope.
• is_function() now recognizes actual function values instead of always returning false.
• echo()/assert() formatting for a function value prints function(params).

Implementation

• Value gains a Function tag holding a closure via a new ClosureEnv struct (declared right after Value to avoid a self-referential-type problem, since Value only ever touches it through shared_ptr indirection).
• New FunctionLit AST node (src/lang/Expr.h) and parser support for function(params) expr as a primary expression (src/lang/Parser.cpp), without disturbing the existing statement-level function name(...) = expr; grammar.
• FunctionCall dispatch now checks whether the callee name is a variable holding a closure before falling back to named function defs / builtins (src/lang/Interpreter.cpp).
• A new Interpreter::assignVar helper centralizes the "real assignment" call sites (global assignments, local block assignments, let(...) bindings) so only those get the self-recursion seeding — parameter/loop-variable binding still uses plain setVar to avoid mutating a closure that arrived as an argument.

Test plan

• New Catch2 unit tests in tests/test_parser.cpp (literal parsing, params/defaults, passing a literal as a call argument, named-def parsing unaffected) and tests/test_interpreter.cpp (basic call, is_function, defaults, lexical capture, higher-order args, self-recursion, copy-aliasing safety).
• Verified end-to-end against the real source files with a standalone harness (the language subsystem has no external deps, so it compiles/runs without the Vulkan/vcpkg toolchain): closures, higher-order args, lexical capture, recursion, aliasing safety, defaults, list storage, and is_function all pass.
• CI green on the branch.

🤖 Generated with Claude Code

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Generated by Claude Code

[particlesector]

Solid implementation overall — closures, lexical capture, and the self-recursion aliasing-safety guard are all handled correctly and well-tested. One real bug found (inline): the self-recursion seeding creates a shared_ptr reference cycle that leaks the closure's environment.

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Generated by Claude Code