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#ifndef ML99_LANG_CLOSURE_H
#define ML99_LANG_CLOSURE_H
#include <metalang99/priv/bool.h>
#include <metalang99/priv/util.h>
#include <metalang99/nat/dec.h>
#include <metalang99/nat/eq.h>
/*
* A closure has the form `(arity, f, ...)`, where `arity` is how many times `ML99_appl` can
* be called for this closure, and `...` denotes the closure's environment.
*
* `ML99_appl` is described by the following algorithm:
* - If `f` is an identifier (like `FOO`):
* - If `f##_ARITY` is 1, then just call this function with provided arguments.
* - Otherwise, return `(f##_ARITY - 1, f, provided args...)`.
* - Otherwise (`f` is a closure):
* - If `arity` is 1, then just call `f` with its environment and provided arguments.
* - Otherwise, return `(arity - 1, f, env..., provided args...)`.
*
* Thus, each time except the last, `ML99_appl` extends a closure's environment with new
* arguments; the last time, it calls `f` with its environment.
*/
#define ML99_appl_IMPL(f, ...) \
ML99_PRIV_IF(ML99_PRIV_IS_UNTUPLE_FAST(f), ML99_PRIV_APPL_F, ML99_PRIV_APPL_CLOSURE) \
(f, __VA_ARGS__)
#define ML99_PRIV_APPL_F(f, ...) \
ML99_PRIV_IF( \
ML99_PRIV_NAT_EQ(f##_ARITY, 1), \
ML99_callUneval(f, __VA_ARGS__), \
v((ML99_PRIV_DEC(f##_ARITY), f, __VA_ARGS__)))
#define ML99_PRIV_APPL_CLOSURE(closure, ...) \
ML99_PRIV_APPL_CLOSURE_AUX(ML99_PRIV_EXPAND closure, __VA_ARGS__)
#define ML99_PRIV_APPL_CLOSURE_AUX(...) ML99_PRIV_APPL_CLOSURE_AUX_AUX(__VA_ARGS__)
#define ML99_PRIV_APPL_CLOSURE_AUX_AUX(arity, f, ...) \
ML99_PRIV_IF( \
ML99_PRIV_NAT_EQ(arity, 1), \
ML99_callUneval(f, __VA_ARGS__), \
v((ML99_PRIV_DEC(arity), f, __VA_ARGS__)))
#define ML99_appl2_IMPL(f, a, b) ML99_appl(ML99_appl_IMPL(f, a), v(b))
#define ML99_appl3_IMPL(f, a, b, c) ML99_appl(ML99_appl2_IMPL(f, a, b), v(c))
#define ML99_appl4_IMPL(f, a, b, c, d) ML99_appl(ML99_appl3_IMPL(f, a, b, c), v(d))
#endif // ML99_LANG_CLOSURE_H
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