Implement function named arguments, ret, and multiple return values

- Add FuncDef struct to symbol.h/symbol.c: holds body token list,
  strdup'd param names, and param count; replaces the bare List* that
  SYM_FUNCTION used to store; funcdef_delete frees param strings and
  body list (tokens are GC-managed)
- Add CONTROL_RET to ControlType so ret can propagate cleanly through
  the interpreter's control-flow stack
- Update _func_decl to parse optional (p1, p2, ...) param list and store
  a FuncDef* instead of a raw List*
- Implement case TT_RET in _control: clears intermediate stack values,
  evaluates comma-separated return expressions, sets CONTROL_RET
- Propagate CONTROL_RET in all loop bodies (while/until, loop, do)
  without clearing it; while/until rescues return values from the
  temporary condition stack before it is destroyed
- Update _term call site to support parenthesised func(arg1, arg2)
  syntax alongside the existing no-parens style for backward compat
- Modify interpret_subprocess to merge the sub's stack into the parent
  when CONTROL_RET is active so return values survive teardown
- Update function_process_self_defined SYM_FUNCTION case to pop and
  bind named args, run the body, then clear CONTROL_RET
- Add -D_POSIX_C_SOURCE=200809L to Makefile CFLAGS for strdup under
  -std=c99 -pedantic
- Add examples/func_args_ret.fy covering zero-arg, single-arg,
  two-arg, conditional ret, multiple return values, and old-style
  no-parens backward compat

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/tags b/tags
index 2ed6274..d29941d 100644
--- a/tags
+++ b/tags
@@ -160,6 +160,8 @@ datiter_new	./src/data/dat.c	/^datiter_new(Dat *p_dat) {$/;"	f	typeref:typename:
 datiter_next	./src/data/dat.c	/^datiter_next(DatIter *p_iter) {$/;"	f	typeref:typename:void *
 datiter_next_t	./src/data/dat.c	/^datiter_next_t(DatIter *p_iter, TYPE *p_type) {$/;"	f	typeref:typename:void *
 datiter_skip	./src/data/dat.c	/^datiter_skip(DatIter *p_iter, unsigned i_num) {$/;"	f	typeref:typename:void
+funcdef_delete	./src/core/symbol.c	/^funcdef_delete(FuncDef *p_funcdef) {$/;"	f	typeref:typename:void
+funcdef_new	./src/core/symbol.c	/^funcdef_new(List *p_body, List *p_params, int i_nparams) {$/;"	f	typeref:typename:FuncDef *
 function_delete	./src/core/function.c	/^function_delete(Function *p_function) {$/;"	f	typeref:typename:void
 function_is_buildin	./src/core/functions.c	/^function_is_buildin(Token *p_token_ident) {$/;"	f	typeref:typename:_Bool
 function_is_self_defined	./src/core/functions.c	/^function_is_self_defined(Interpret *p_interpret) {$/;"	f	typeref:typename:_Bool