/*
  Copyright (C) 2019, 2020 Leo Tenenbaum.
  This file is part of toc. toc is distributed under version 3 of the GNU General Public License, without any warranty whatsoever.
  You should have received a copy of the GNU General Public License along with toc. If not, see <https://www.gnu.org/licenses/>.
*/
static void cgen_create(CGenerator *g, FILE *out, Identifiers *ids, Allocator *allocr) {
	g->outc = out;
	g->ident_counter = 0;
	g->main_ident = ident_get(ids, "main");
	g->will_indent = true;
	g->indent_lvl = 0;
	g->globals = ids;
	g->allocr = allocr;
	g->nms_prefixes = NULL;
}

static void cgen_stmt(CGenerator *g, Statement *s);
enum {
	  CGEN_BLOCK_NOBRACES = 0x01 /* should it use braces? */
};
static void cgen_block(CGenerator *g, Block *b, const char *ret_name, uint16_t flags);
static void cgen_expr_pre(CGenerator *g, Expression *e);
static void cgen_expr(CGenerator *g, Expression *e);
static void cgen_set(CGenerator *g, Expression *set_expr, const char *set_str, Expression *to_expr,
					 const char *to_str);
static void cgen_set_tuple(CGenerator *g, Expression *exprs, Identifier *idents, const char *prefix, Expression *to);
static void cgen_type_pre(CGenerator *g, Type *t);
static void cgen_type_post(CGenerator *g, Type *t);
static void cgen_decl(CGenerator *g, Declaration *d);
static void cgen_ret(CGenerator *g, Expression *ret);
static void cgen_val(CGenerator *g, Value v, Type *t);
static void cgen_val_pre(CGenerator *g, Value v, Type *t);
static void cgen_val_ptr(CGenerator *g, void *v, Type *t);
static void cgen_defs_block(CGenerator *g, Block *b);
static void cgen_defs_decl(CGenerator *g, Declaration *d);

#define cgen_recurse_subexprs_fn_simple(fn, decl_f, block_f)	\
	if (!(fn->flags & FN_EXPR_FOREIGN)) {						\
		FnExpr *prev_fn = g->f##n;								\
		g->f##n = fn;											\
		arr_foreach(fn->params, Declaration, param)				\
			decl_f(g, param);									\
		arr_foreach(fn->ret_decls, Declaration, r)				\
			decl_f(g, r);										\
		block_f(g, &fn->body);									\
		g->f##n = prev_fn;										\
	}

/* calls f on every sub-expression of e, block_f on every sub-block, and decl_f on every sub-declaration. */
#define cgen_recurse_subexprs(g, e, f, block_f, decl_f)					\
	switch (e->kind) {													\
	case EXPR_TYPE:														\
	case EXPR_VAL:														\
	case EXPR_C:														\
	case EXPR_BUILTIN:													\
	case EXPR_IDENT:													\
	case EXPR_LITERAL_BOOL:												\
	case EXPR_LITERAL_INT:												\
	case EXPR_LITERAL_STR:												\
	case EXPR_LITERAL_CHAR:												\
	case EXPR_LITERAL_FLOAT:											\
		break;															\
	case EXPR_UNARY_OP:													\
		f(g, e->unary.of);												\
		break;															\
	case EXPR_BINARY_OP:												\
		f(g, e->binary.lhs);											\
		if (e->binary.op != BINARY_DOT)									\
			f(g, e->binary.rhs);										\
		break;															\
	case EXPR_CAST:														\
		f(g, e->cast.expr);												\
		break;															\
	case EXPR_CALL:														\
		f(g, e->call.fn);												\
		arr_foreach(e->call.arg_exprs, Expression, arg)					\
			f(g, arg);													\
		break;															\
	case EXPR_BLOCK:													\
		block_f(g, e->block);											\
		break;															\
	case EXPR_NMS: {													\
		Namespace *prev = g->nms;										\
		g->nms = e->nms;												\
		block_f(g, &e->nms->body);										\
		g->nms = prev;													\
	} break;															\
	case EXPR_IF: {														\
		IfExpr *i = e->if_;												\
		if (i->cond)													\
			f(g, i->cond);												\
		block_f(g, &i->body);											\
		if (i->next_elif)												\
			f(g, i->next_elif);											\
	} break;															\
	case EXPR_WHILE: {													\
		WhileExpr *w = e->while_;										\
		if (w->cond)													\
			f(g, w->cond);												\
		block_f(g, &w->body);											\
	} break;															\
	case EXPR_FOR: {													\
		ForExpr *fo = e->for_;											\
		if (fo->flags & FOR_IS_RANGE) {									\
			f(g, fo->range.from);										\
			if (fo->range.to) f(g, fo->range.to);						\
			/* step is a value, not an expression */					\
		} else {														\
			f(g, fo->of);												\
		}																\
		block_f(g, &fo->body);											\
	} break;															\
	case EXPR_TUPLE:													\
		arr_foreach(e->tuple, Expression, x)							\
			f(g, x);													\
		break;															\
	case EXPR_SLICE:													\
		f(g, e->slice.of);												\
		if (e->slice.from) f(g, e->slice.from);							\
		if (e->slice.to) f(g, e->slice.to);								\
		break;															\
	case EXPR_FN: {														\
		FnExpr *fn = e->fn;												\
		if (fn_has_instances(fn)) {										\
			Instance **data = fn->instances->data;						\
			for (U64 i = 0; i < fn->instances->cap; ++i) {				\
				if (fn->instances->occupied[i]) {						\
					cgen_recurse_subexprs_fn_simple(((*data)->fn), decl_f, block_f); \
				}														\
				++data;													\
			}															\
	 	} else {														\
			cgen_recurse_subexprs_fn_simple(fn, decl_f, block_f);		\
		}																\
	} break;															\
	case EXPR_NEW:														\
		if (e->new.n) f(g, e->new.n);									\
		break;															\
	}


#define cgen_recurse_subtypes(f, g, type)			\
	switch (type->kind) {							\
	case TYPE_STRUCT:								\
		/* don't descend into fields */				\
		break;										\
	case TYPE_FN:									\
		arr_foreach(type->fn.types, Type, sub) {	\
			f(g, sub);								\
		}											\
		break;										\
	case TYPE_TUPLE:								\
		arr_foreach(type->tuple, Type, sub)			\
			f(g, sub);								\
		break;										\
	case TYPE_ARR:									\
		f(g, type->arr.of);							\
		break;										\
	case TYPE_SLICE:								\
		f(g, type->slice);							\
		break;										\
	case TYPE_PTR:									\
		f(g, type->ptr);							\
		break;										\
	case TYPE_VOID:									\
	case TYPE_BUILTIN:								\
	case TYPE_UNKNOWN:								\
		break;										\
	case TYPE_EXPR: assert(0);						\
	}



static inline FILE *cgen_writing_to(CGenerator *g) {
	return g->outc;	/* for now */
}

static inline void *cgen_malloc(CGenerator *g, size_t sz) {
	return allocr_malloc(g->allocr, sz);
}

/* indent iff needed */
static inline void cgen_indent(CGenerator *g) {
	if (g->will_indent) {
		for (int i = 0; i < g->indent_lvl; ++i)
			fprintf(cgen_writing_to(g), "\t");
		g->will_indent = false;
	}
}

static inline void cgen_write(CGenerator *g, const char *fmt, ...) {
	va_list args;
	cgen_indent(g);
	va_start(args, fmt);
	vfprintf(cgen_writing_to(g), fmt, args);
	va_end(args);
#ifdef TOC_DEBUG
	fflush(cgen_writing_to(g));
#endif
}

static inline void cgen_nl(CGenerator *g) {
	fprintf(cgen_writing_to(g), "\n");
	g->will_indent = true;
}

static inline char *cgen_ident_to_str(Identifier i) {
	return ident_to_str_reduced_charset(i);
}

static inline void cgen_ident_id(CGenerator *g, IdentID id) {
	cgen_write(g, "a%lu_", (unsigned long)id);
}
/* used for fields */
static inline void cgen_ident_simple(CGenerator *g, Identifier i) {
	cgen_indent(g);
	fprint_ident_reduced_charset(cgen_writing_to(g), i);
}

static void cgen_ident(CGenerator *g, Identifier i) {
	if (i->nms) {
		cgen_write(g, "%s", i->nms->c.prefix);
	}
	if (i == g->main_ident && i->decl_kind == IDECL_DECL && ident_scope(i) == NULL) {
		/* don't conflict with C's main! */
		cgen_write(g, "main_");
	} else {
	    cgen_ident_simple(g, i);
	}
}


#define CGEN_IDENT_ID_STR_SIZE 32
/* buffer should be at least CGEN_IDENT_ID_STR_SIZE bytes */
static inline void cgen_ident_id_to_str(char *buffer, IdentID id) {
	snprintf(buffer, CGEN_IDENT_ID_STR_SIZE, "a%lu_", (unsigned long)id);
}

static inline void cgen_writeln(CGenerator *g, const char *fmt, ...) {
	va_list args;
	cgen_indent(g);
	va_start(args, fmt);
	vfprintf(cgen_writing_to(g), fmt, args);
	va_end(args);
	cgen_nl(g);
}

/* should this declaration be a direct function declaration C? (as opposed to using a function pointer or not being a function) */
static bool cgen_fn_is_direct(CGenerator *g, Declaration *d) {
	return (g->block == NULL || (g->block->flags & BLOCK_IS_NMS)) && (d->flags & DECL_HAS_EXPR) && d->expr.kind == EXPR_FN && arr_len(d->idents) == 1;
}

static bool fn_has_instances(FnExpr *f) {
	if (fn_has_any_const_params(f)) return true;
	if (!arr_len(f->params)) return false;
	return type_is_builtin(&((Declaration *)arr_last(f->params))->type, BUILTIN_VARARGS);
}

static bool cgen_uses_ptr(Type *t) {
	assert(t->flags & TYPE_IS_RESOLVED);
	switch (t->kind) {
	case TYPE_TUPLE:
	case TYPE_STRUCT:
	case TYPE_ARR:
		return true;
	case TYPE_BUILTIN:
	case TYPE_PTR:
	case TYPE_FN:
	case TYPE_SLICE:
	case TYPE_VOID:
	case TYPE_UNKNOWN:
		return false;
	case TYPE_EXPR:
		break;
	}
	assert(0);
	return false;
}

static void cgen_struct_name(CGenerator *g, StructDef *sdef) {
	if (sdef->name) {
		cgen_ident(g, sdef->name);
	} else {
		assert(sdef->c.id);
		cgen_ident_id(g, sdef->c.id);
	}
	if (sdef->instance_id) {
		possibly_static_assert(sizeof sdef->instance_id == 8);
		cgen_write(g, U64_FMT, sdef->instance_id);
	}
}

static void cgen_type_pre(CGenerator *g, Type *t) {
	assert(t->flags & TYPE_IS_RESOLVED);
	switch (t->kind) {
	case TYPE_BUILTIN:
		switch (t->builtin) {
		case BUILTIN_I8: cgen_write(g, "i8"); break;
		case BUILTIN_I16: cgen_write(g, "i16"); break;
		case BUILTIN_I32: cgen_write(g, "i32"); break;
		case BUILTIN_I64: cgen_write(g, "i64"); break;
		case BUILTIN_U8: cgen_write(g, "u8"); break;
		case BUILTIN_U16: cgen_write(g, "u16"); break;
		case BUILTIN_U32: cgen_write(g, "u32"); break;
		case BUILTIN_U64: cgen_write(g, "u64"); break;
		case BUILTIN_CHAR: cgen_write(g, "char"); break;
		case BUILTIN_BOOL: cgen_write(g, "bool"); break;
		case BUILTIN_F32: cgen_write(g, "f32"); break;
		case BUILTIN_F64: cgen_write(g, "f64"); break;
		case BUILTIN_NMS:
		case BUILTIN_TYPE:
		case BUILTIN_VARARGS:
			assert(0); break;
		} break;
	case TYPE_PTR:
		cgen_type_pre(g, t->ptr);
		cgen_write(g, "(*");
		break;
	case TYPE_ARR:
		cgen_type_pre(g, t->arr.of);
		cgen_write(g, "(");
		break;
	case TYPE_FN:
		if (cgen_uses_ptr(&t->fn.types[0])) {
			cgen_write(g, "void");
		} else {
			cgen_type_pre(g, &t->fn.types[0]);
		}
		cgen_write(g, " (*");
		break;
	case TYPE_SLICE:
		cgen_write(g, "slice_");
		break;
	case TYPE_VOID: cgen_write(g, "void"); break;
	case TYPE_STRUCT:
		cgen_write(g, "struct ");
		cgen_struct_name(g, t->struc);
		break;
	case TYPE_TUPLE:
	case TYPE_EXPR:
	case TYPE_UNKNOWN:
		/* We should never try to generate this type */
		assert(0);
		break;
	}
}

static void cgen_type_post(CGenerator *g, Type *t) {
	assert(t->flags & TYPE_IS_RESOLVED);
	switch (t->kind) {
	case TYPE_PTR:
		cgen_write(g, ")");
	    cgen_type_post(g, t->ptr);
		break;
	case TYPE_ARR:
		assert(t->flags & TYPE_IS_RESOLVED);
		cgen_write(g, "[%lu])", (unsigned long)t->arr.n);
		cgen_type_post(g, t->arr.of);
		break;
	case TYPE_FN: {
		bool out_param = cgen_uses_ptr(&t->fn.types[0]);
		cgen_write(g, ")(");
		for (size_t i = 1; i < arr_len(t->fn.types); ++i) {
			if (i != 1)
				cgen_write(g, ", ");
			cgen_type_pre(g, &t->fn.types[i]);
			if (cgen_uses_ptr(&t->fn.types[i]))
				cgen_write(g, "(*)");
			cgen_type_post(g, &t->fn.types[i]);
		}
		if (out_param) {
			Type *ret_type = &t->fn.types[0];
			if (arr_len(t->fn.types) > 1)
				cgen_write(g, ", ");
			if (ret_type->kind == TYPE_TUPLE) {
				arr_foreach(ret_type->tuple, Type, x) {
					cgen_type_pre(g, x);
					cgen_write(g, "(*)");
					cgen_type_post(g, x);
					if (x != arr_last(ret_type->tuple)) {
						cgen_write(g, ", ");
					}
				}
			} else {
				cgen_type_pre(g, ret_type);
				cgen_write(g, "(*)");
				cgen_type_post(g, ret_type);
			}
		}
		if (arr_len(t->fn.types) == 1 && !out_param)
			cgen_write(g, "void");
		cgen_write(g, ")");
		if (!out_param)
			cgen_type_post(g, &t->fn.types[0]);
	} break;
	case TYPE_BUILTIN:
	case TYPE_VOID:
	case TYPE_UNKNOWN:
	case TYPE_TUPLE:
	case TYPE_SLICE:
	case TYPE_STRUCT:
		break;
	case TYPE_EXPR:
		assert(0);
		break;
	}
}

static inline void cgen_fn_name(CGenerator *g, FnExpr *f) {
	if (f->c.name) {
		cgen_ident(g, f->c.name);
	} else {
		cgen_ident_id(g, f->c.id);
	}
}

static inline void cgen_fn_instance_number(CGenerator *g, U64 instance) {
	cgen_write(g, U64_FMT "_", instance);
}

/* should we generate this function? (or is it just meant for compile time) */
static bool cgen_should_gen_fn(FnExpr *f) {
	if (f->flags & FN_EXPR_FOREIGN)
		return true;
	else if (f->ret_decls) {
		arr_foreach(f->ret_decls, Declaration, decl)
			if (type_is_compileonly(&decl->type))
				return false;
		return true;
	} else {
		return !type_is_compileonly(&f->ret_type);
	}
}

static void cgen_full_fn_name(CGenerator *g, FnExpr *f) {
	cgen_fn_name(g, f);
	if (f->instance_id) {
		cgen_fn_instance_number(g, f->instance_id);
	}
}

static void cgen_val_ptr_pre(CGenerator *g, void *v, Type *t) {
	assert(t->flags & TYPE_IS_RESOLVED);
	switch (t->kind) {
	case TYPE_SLICE: {
		Slice *s = (Slice *)v;
		for (I64 i = 0; i < s->n; ++i) {
			cgen_val_ptr_pre(g, (char *)s->data + (U64)i * compiler_sizeof(t->slice), t->slice);
		}
	    cgen_type_pre(g, t->slice);
		cgen_write(g, "(d%p_[])", v); /* TODO: improve this somehow? */
		cgen_type_post(g, t->slice);
		cgen_write(g, " = {");
		for (I64 i = 0; i < s->n; ++i) {
			if (i) cgen_write(g, ", ");
			cgen_val_ptr(g, (char *)s->data + (U64)i * compiler_sizeof(t->slice), t->slice);
		}
		cgen_write(g, "};");
		cgen_nl(g);
	} break;
	case TYPE_ARR:
		for (size_t i = 0; i < t->arr.n; ++i) {
			cgen_val_ptr_pre(g, (char *)*(void **)v + i * compiler_sizeof(t->arr.of), t->arr.of);
		}
		break;
	case TYPE_FN:
	case TYPE_UNKNOWN:
	case TYPE_TUPLE:
	case TYPE_VOID:
	case TYPE_BUILTIN:
	case TYPE_PTR:
	case TYPE_STRUCT:
		break;
	case TYPE_EXPR:
		assert(0);
		break;
	}
}

/* generate a value from a pointer */
static void cgen_val_ptr(CGenerator *g, void *v, Type *t) {
	assert(t->flags & TYPE_IS_RESOLVED);
	switch (t->kind) {
	case TYPE_TUPLE:
	case TYPE_VOID:
	case TYPE_EXPR:
	case TYPE_UNKNOWN:
		assert(0);
		return;
	case TYPE_ARR:
		cgen_write(g, "{");
		for (size_t i = 0; i < t->arr.n; ++i) {
			if (i) cgen_write(g, ", ");
			cgen_val_ptr(g, (char *)v + i * compiler_sizeof(t->arr.of), t->arr.of);
		}
		cgen_write(g, "}");
		break;
	case TYPE_SLICE:
		cgen_write(g, "{d%p_, %lu}", v, ((Slice *)v)->n);
		break;
	case TYPE_STRUCT:
		cgen_write(g, "{");
		arr_foreach(t->struc->fields, Field, f) {
			if (f != t->struc->fields)
				cgen_write(g, ", ");
			cgen_val_ptr(g, (char *)v + f->offset, &f->type);
		}
		cgen_write(g, "}");
		break;
	case TYPE_FN:
		cgen_fn_name(g, *(FnExpr **)v);
		break;
	case TYPE_PTR:
		/* You can't have a constant pointer. */
		assert(0);
		break;
	case TYPE_BUILTIN:
		switch (t->builtin) {
		case BUILTIN_I8: cgen_write(g, I8_FMT, *(I8 *)v); break;
		case BUILTIN_U8: cgen_write(g, U8_FMT, *(U8 *)v); break;
		case BUILTIN_I16: cgen_write(g, I16_FMT, *(I16 *)v); break;
		case BUILTIN_U16: cgen_write(g, U16_FMT, *(U16 *)v); break;
		case BUILTIN_I32: cgen_write(g, I32_FMT, *(I32 *)v); break;
		case BUILTIN_U32: cgen_write(g, U32_FMT, *(U32 *)v); break;
		case BUILTIN_I64: cgen_write(g, I64_FMT, *(I64 *)v); break;
		case BUILTIN_U64: cgen_write(g, U64_FMT, *(U64 *)v); break;
		case BUILTIN_F32: cgen_write(g, F32_FMT "f", *(F32 *)v); break;
		case BUILTIN_F64: cgen_write(g, F64_FMT, *(F64 *)v); break;
		case BUILTIN_CHAR: cgen_write(g, "'\\x%02x'", *(char *)v); break;
		case BUILTIN_BOOL: cgen_write(g, "%s", *(bool *)v ? "true" : "false"); break;
		case BUILTIN_TYPE:
		case BUILTIN_NMS:
		case BUILTIN_VARARGS:
			assert(0);
			break;
		}
		break;
	}
}

static void cgen_val_pre(CGenerator *g, Value v, Type *t) {
	cgen_val_ptr_pre(g, val_get_ptr(&v, t), t);
}

/* generates a value fit for use as an initializer */
static void cgen_val(CGenerator *g, Value v, Type *t) {
	cgen_val_ptr(g, val_get_ptr(&v, t), t);
}

/* can the value generated by cgen_val for this type be used directly (as opposed to being stored in a variable)? */
static inline bool cgen_is_type_simple(Type *t) {
	return t->kind == TYPE_BUILTIN || t->kind == TYPE_FN;
}

static void cgen_fn_params(CGenerator *g, FnExpr *f, U64 which_are_const) {
	bool out_param = cgen_uses_ptr(&f->ret_type);
	cgen_write(g, "(");
	int semi_const_idx = 0;
	bool any_params = false;
	arr_foreach(f->params, Declaration, d) {
		if (d->flags & DECL_IS_CONST) continue;
		if (type_is_builtin(&d->type, BUILTIN_VARARGS)) {
			int idx = 0;
			arr_foreach(d->val.varargs, VarArg, varg) {
				if (any_params) 
					cgen_write(g, ", ");
				any_params = true;
				cgen_type_pre(g, varg->type);
				cgen_write(g, " ");
				cgen_ident_simple(g, d->idents[0]);
				cgen_write(g, "%d_", idx);
				cgen_type_post(g, varg->type);
				++idx;
			}
		} else if ((d->flags & DECL_SEMI_CONST)
				   && (which_are_const & (((U64)1) << semi_const_idx++))) {
			/* semi constant argument is constant */
		} else {
		    int idx = 0;
			arr_foreach(d->idents, Identifier, i) {
				if (any_params) 
					cgen_write(g, ", ");
				any_params = true;
				Type *type = d->type.kind == TYPE_TUPLE ? &d->type.tuple[idx++] : &d->type;
				cgen_type_pre(g, type);
				cgen_write(g, " ");
				cgen_ident_simple(g, *i);
				cgen_type_post(g, type);
			}
		}
	}
	if (out_param) {
		if (f->ret_type.kind == TYPE_TUPLE) {
			/* multiple return variables */
			for (size_t i = 0; i < arr_len(f->ret_type.tuple); ++i) {
				Type *x = &f->ret_type.tuple[i];
				if (any_params || i > 0)
					cgen_write(g, ", ");
				cgen_type_pre(g, x);
				cgen_write(g, "(*ret__%lu)", (unsigned long)i);
				cgen_type_post(g, x);
			}
		} else {
			if (any_params)
				cgen_write(g, ", ");
			cgen_type_pre(g, &f->ret_type);
			cgen_write(g, " (*ret__)");
			cgen_type_post(g, &f->ret_type);
		}
		any_params = true;
	}
	if (!any_params)
		cgen_write(g, "void");
	cgen_write(g, ")");
}

static inline void cgen_arg_pre(CGenerator *g, Expression *arg) {
	cgen_expr_pre(g, arg);
	if (arg->type.kind == TYPE_ARR) {
		/* create copy of array */
		IdentID copy = ++g->ident_counter;
		cgen_type_pre(g, &arg->type);
		char s[CGEN_IDENT_ID_STR_SIZE];
		cgen_ident_id_to_str(s, copy);

		cgen_write(g, " %s", s);
		cgen_type_post(g, &arg->type);
		cgen_write(g, "; ");
		cgen_set(g, NULL, s, arg, NULL);
		arg->cgen.id = copy;
	}
}

static inline void cgen_arg(CGenerator *g, Expression *arg) {
	if (arg->type.kind == TYPE_ARR) {
		cgen_ident_id(g, arg->cgen.id);
	} else {
		cgen_expr(g, arg);
	}
}

/* unless f has const/semi-const args, which_are_const can be set to 0 */
static void cgen_fn_header(CGenerator *g, FnExpr *f, U64 which_are_const) {
	assert(!(f->flags & FN_EXPR_FOREIGN));
	
	bool out_param = cgen_uses_ptr(&f->ret_type);
	assert(cgen_should_gen_fn(f));
	if (!(f->flags & FN_EXPR_EXPORT))
		cgen_write(g, "static ");
	if (out_param) {
		cgen_write(g, "void ");
	} else {
		cgen_type_pre(g, &f->ret_type);
		cgen_write(g, " ");
	}
	cgen_full_fn_name(g, f);	
    cgen_fn_params(g, f, which_are_const);
	if (!out_param) {
		cgen_type_post(g, &f->ret_type);
	}
}


/* 
   Either set_expr or set_str should be NULL and either to_expr or to_str should be NULL 
   Also, set_str and/or to_str should be NULL
   this DOES NOT call cgen_expr_pre for set_expr or to_expr
*/
static void cgen_set(CGenerator *g, Expression *set_expr, const char *set_str, Expression *to_expr,
					 const char *to_str) {
	Type *type;
	if (set_expr) {
		type = &set_expr->type;
	} else {
		assert(to_expr);
		type = &to_expr->type;
	}
	switch (type->kind) {
	case TYPE_BUILTIN:
	case TYPE_FN:
	case TYPE_PTR:
	case TYPE_SLICE:
	case TYPE_STRUCT:
	case TYPE_UNKNOWN:
		if (set_expr) {
			cgen_expr(g, set_expr);
		} else {
			cgen_write(g, set_str);
		}
		cgen_write(g, " = ");
		if (to_expr) {
			cgen_expr(g, to_expr);
		} else {
			cgen_write(g, to_str);
		}
		cgen_write(g, ";");
		break;
	case TYPE_ARR:
		cgen_write(g, "{");
		cgen_nl(g);
		cgen_write(g, "size_t i;");
		cgen_type_pre(g, type->arr.of);
		cgen_write(g, "(*arr__in)");
		cgen_type_post(g, type->arr.of);
		cgen_write(g, " = ");
		if (to_expr) {
			cgen_expr(g, to_expr);
		} else {
			cgen_write(g, to_str);
		}
		cgen_write(g, "; ");
		cgen_type_pre(g, type->arr.of);
		cgen_write(g, "(*arr__out)");
		cgen_type_post(g, type->arr.of);
		cgen_write(g, " = ");
		if (set_expr) {
			cgen_expr(g, set_expr);
		} else {
			cgen_write(g, set_str);
		}
		cgen_write(g, ";");
		cgen_nl(g);
		cgen_write(g, "for (i = 0; i < %lu; ++i) arr__out[i] = arr__in[i];", (unsigned long)type->arr.n);
		cgen_nl(g);
		cgen_write(g, "}");
		break;
	case TYPE_TUPLE:
		assert(set_expr);
		assert(to_expr);
		assert(set_expr->kind == EXPR_TUPLE);
		cgen_set_tuple(g, set_expr->tuple, NULL, NULL, to_expr);
		break;
	case TYPE_VOID:
	case TYPE_EXPR:
		assert(0);
		break;
	}
}

/* one of exprs, idents, and prefix should be NULL. does NOT call cgen_expr_pre for to/exprs */
static void cgen_set_tuple(CGenerator *g, Expression *exprs, Identifier *idents, const char *prefix, Expression *to) {
	switch (to->kind) {
	case EXPR_VAL:
		assert(0); /* never needed at the moment */
		break;
	case EXPR_TUPLE:
		/* e.g. a, b = 3, 5; */
		if (exprs) {
			for (size_t i = 0; i < arr_len(to->tuple); ++i) {
				cgen_expr_pre(g, &exprs[i]);
			}
		}
		for (size_t i = 0; i < arr_len(to->tuple); ++i) {
			char *s = NULL, buf[64];
			Expression *e = NULL;
			if (idents)
				s = cgen_ident_to_str(idents[i]);
			else if (exprs)
				e = &exprs[i];
			else {
				snprintf(buf, sizeof buf, "(%s%lu)", prefix, (unsigned long)i);
				s = buf;
			}
			cgen_set(g, e, s, &to->tuple[i], NULL);
			if (s != buf) free(s);
		}
		break;
	case EXPR_CALL: {
		FnType *fn_type = &to->call.fn->type.fn;
		Type *ret_type = &fn_type->types[0];
		Constness *constness = fn_type->constness;
		int i = 0;

		IdentID *underscore_ids = NULL;

		
		int nout_params = (int)(exprs ? arr_len(exprs) : arr_len(idents));
		
		if (idents) {
			for (i = 0; i < nout_params; ++i) {
				if (ident_eq_str(idents[i], "_")) {
					Type *type = &ret_type->tuple[i];
					IdentID id = ++g->ident_counter;
					cgen_type_pre(g, type);
					cgen_write(g, " ");
					cgen_ident_id(g, id);
					cgen_type_post(g, type);
					cgen_write(g, "; ");
					*(IdentID *)arr_add(&underscore_ids) = id;
				}
			}
		}
		
		/* e.g. a, b = fn_which_returns_tuple(); */
		arr_foreach(to->call.arg_exprs, Expression, arg) {
			if (!constness || !arg_is_const(arg, constness[i])) {
				cgen_arg_pre(g, arg);
			}
		}

		cgen_expr_pre(g, to->call.fn);
		cgen_expr(g, to->call.fn);
		
		if (to->call.instance)
			cgen_fn_instance_number(g, to->call.instance->fn->instance_id);
		cgen_write(g, "(");
		bool any_args = false;
		i = 0;
		arr_foreach(to->call.arg_exprs, Expression, arg) {
			if (!constness || !arg_is_const(arg, constness[i])) {
				if (any_args)
					cgen_write(g, ", ");
				any_args = true;
				cgen_arg(g, arg);
			}
			++i;
		}
		/* out params */
		IdentID *u = underscore_ids;
		for (i = 0; i < (int)nout_params; ++i) {
			if (any_args || i > 0)
				cgen_write(g, ", ");
			if (exprs) {
				cgen_write(g, "&");
				cgen_expr(g, &exprs[i]);
			} else if (idents) {
				cgen_write(g, "&");
				if (ident_eq_str(idents[i], "_"))
					cgen_ident_id(g, *u++);
				else
					cgen_ident(g, idents[i]);
			} else {
				cgen_write(g, "&(%s%d_)", prefix, i);
			}
		}
		arr_clear(&underscore_ids);
		cgen_writeln(g, "); ");
	} break;
	case EXPR_IF:
	case EXPR_BLOCK:
	case EXPR_WHILE:
	case EXPR_FOR: {
		IdentID prefix_id = to->cgen.id = ++g->ident_counter;
		if (exprs) {
			for (size_t i = 0; i < arr_len(to->type.tuple); ++i) {
				cgen_expr_pre(g, &exprs[i]);
			}
		}
		for (unsigned long i = 0; i < (unsigned long)arr_len(to->type.tuple); ++i) {
			cgen_write(g, "(");
			if (exprs) {
				cgen_expr(g, &exprs[i]);
			} else if (idents) {
				cgen_ident(g, idents[i]);
			} else {
				cgen_write(g, "%s%lu", prefix, i);
			}
			cgen_write(g, ") = ");
			cgen_ident_id(g, prefix_id);
			cgen_write(g, "%lu", i);
			cgen_write(g, "; ");
		}
	} break;
		/* things which can never be tuples */
	case EXPR_SLICE:
	case EXPR_IDENT:
	case EXPR_LITERAL_INT:
	case EXPR_LITERAL_CHAR:
	case EXPR_LITERAL_BOOL:
	case EXPR_LITERAL_STR:
	case EXPR_LITERAL_FLOAT:
	case EXPR_UNARY_OP:
	case EXPR_BINARY_OP:
	case EXPR_FN:
	case EXPR_CAST:
	case EXPR_NEW:
	case EXPR_C:
	case EXPR_BUILTIN:
	case EXPR_TYPE:
	case EXPR_NMS:
		assert(0);
		break;
	}
}

static void cgen_expr_pre(CGenerator *g, Expression *e) {
	IdentID id = 0;
	char ret_name[CGEN_IDENT_ID_STR_SIZE+20];
	switch (e->kind) {
	case EXPR_IF:
	case EXPR_WHILE:
	case EXPR_FOR:
	case EXPR_BLOCK: {
		id = ++g->ident_counter;
		
		cgen_ident_id_to_str(ret_name, id);
		char *p = ret_name + strlen(ret_name);
		if (e->type.kind != TYPE_VOID) {
			if (e->type.kind == TYPE_TUPLE) {
				for (unsigned long i = 0; i < arr_len(e->type.tuple); ++i) {
					sprintf(p, "%lu", i);
					cgen_type_pre(g, &e->type.tuple[i]);
					cgen_write(g, " %s", ret_name);
					cgen_type_post(g, &e->type.tuple[i]);
					cgen_write(g, "; ");
				}
			
			} else {
				cgen_type_pre(g, &e->type);
				cgen_write(g, " %s", ret_name);
				cgen_type_post(g, &e->type);
				cgen_write(g, ";");
				cgen_nl(g);
			}
		}
		*p = 0; /* clear tuple suffixes */
		
	} break;
	default: break;
	}
	
	switch (e->kind) {
	case EXPR_IF: {
		IfExpr *curr = e->if_;
		e->cgen.id = id;
		while (1) {
			if (curr->cond) {
				cgen_write(g, "if (");
				cgen_expr(g, curr->cond);
				cgen_write(g, ") ");
			}
			cgen_block(g, &curr->body, ret_name, 0);
			if (curr->next_elif) {
				cgen_write(g, " else ");
				curr = curr->next_elif->if_;
			} else break;
		}
	} break;
	case EXPR_WHILE: {
		WhileExpr *w = e->while_;
		e->cgen.id = id;
		cgen_write(g, "while (");
		if (w->cond) {
			cgen_expr(g, w->cond);
		} else {
			cgen_write(g, "true");
		}
		cgen_write(g, ") ");
		cgen_block(g, &w->body, ret_name, 0);
	} break;
	case EXPR_FOR: {
		ForExpr *fo = e->for_;
		int is_range = fo->flags & FOR_IS_RANGE;
		if (is_range) {
			cgen_expr_pre(g, fo->range.from);
			if (fo->range.to)
				cgen_expr_pre(g, fo->range.to);
		} else {
			cgen_expr_pre(g, fo->of);
		}
		e->cgen.id = id;
		cgen_write(g, "{");
		if (is_range) {
			if (fo->range.to) {
				/* pre generate to */
				cgen_type_pre(g, &fo->type);
				cgen_write(g, " to_");
				cgen_type_post(g, &fo->type);
				cgen_write(g, " = ");
				cgen_expr(g, fo->range.to);
				cgen_write(g, "; ");
			}
			
			/* set value to from */
			if (fo->value) {
				cgen_type_pre(g, &fo->type);
				cgen_write(g, " ");
				cgen_ident(g, fo->value);
				cgen_type_post(g, &fo->type);
				cgen_write(g, "; ");
				Expression val_expr;
				val_expr.flags = EXPR_FOUND_TYPE;
				val_expr.kind = EXPR_IDENT;
				val_expr.ident = fo->value;
				val_expr.type = fo->type;
				cgen_set(g, &val_expr, NULL, fo->range.from, NULL);
			} else {
				cgen_type_pre(g, &fo->type);
				cgen_write(g, " val_");
				cgen_type_post(g, &fo->type);
				cgen_write(g, "; ");
				cgen_set(g, NULL, "val_", fo->range.from, NULL);
			}
		} else {
			/* pre-generate of */
			cgen_type_pre(g, &fo->of->type);
			cgen_write(g, " of_");
			cgen_type_post(g, &fo->of->type);
			cgen_write(g, "; ");
			
			cgen_set(g, NULL, "of_", fo->of, NULL);
		}
		cgen_write(g, "for (");
		if (fo->index || !is_range) {
			cgen_write(g, "i64 ");
			if (fo->index)
				cgen_ident(g, fo->index);
			else
				cgen_write(g, "i_");
			cgen_write(g, " = 0");
		}
		cgen_write(g, "; ");
		bool uses_ptr = false;
		Type *of_type = NULL;
		if (!(is_range && !fo->range.to)) { /* if it's finite */
			if (is_range) {
				if (fo->value)
					cgen_ident(g, fo->value);
				else
					cgen_write(g, "val_");
				bool positive_step
					= fo->range.stepval == NULL || val_is_nonnegative(*fo->range.stepval, &fo->type);
				cgen_write(g, " %c= to_", positive_step ? '<' : '>');
			} else {
				if (fo->index)
					cgen_ident(g, fo->index);
				else
					cgen_write(g, "i_");
				cgen_write(g, " < ");
				of_type = &fo->of->type;
				uses_ptr = of_type->kind == TYPE_PTR;
				if (uses_ptr) {
					of_type = of_type->ptr;
				}
				switch (of_type->kind) {
				case TYPE_ARR:
					cgen_write(g, "%lu", (unsigned long)of_type->arr.n);
					break;
				case TYPE_SLICE:
					cgen_write(g, "of_%sn", uses_ptr ? "->" : ".");
					break;
				default: assert(0); break;
				}
			}
		}
		cgen_write(g, "; ");
		if (is_range) {
			if (fo->range.stepval) {
				cgen_val_pre(g, *fo->range.stepval, &fo->type);
			}
			if (fo->value)
				cgen_ident(g, fo->value);
			else
				cgen_write(g, "val_");
			cgen_write(g, " += ");
			if (fo->range.stepval) {
				cgen_val(g, *fo->range.stepval, &fo->type);
			} else {
				cgen_write(g, "1");
			}
			if (fo->index) cgen_write(g, ", ");
		}
		if (fo->index || !is_range) {
			if (fo->index)
				cgen_ident(g, fo->index);
			else
				cgen_write(g, "i_");
			cgen_write(g, "++");
		}
		cgen_write(g, ") {");
		cgen_nl(g);
		if (fo->value) {
			if (!is_range) {
				/* necessary for iterating over, e.g., an array of arrays */
				cgen_type_pre(g, &fo->type);
				if (uses_ptr)
					cgen_write(g, " p_");
				else
					cgen_write(g, "(*p_)");
				cgen_type_post(g, &fo->type);
				cgen_write(g, " = ");
				if (of_type->kind == TYPE_SLICE) {
					cgen_write(g, "((");
					cgen_type_pre(g, &fo->type);
					if (!uses_ptr) cgen_write(g, "(*)");
					cgen_type_post(g, &fo->type);
					cgen_write(g, ")of_%sdata) + ", uses_ptr ? "->" : ".");
					if (fo->index)
						cgen_ident(g, fo->index);
					else
						cgen_write(g, "i_");
				} else {
					cgen_write(g, "&%sof_%s[", uses_ptr ? "(*" : "", uses_ptr ? ")" : "");
					if (fo->index)
						cgen_ident(g, fo->index);
					else
						cgen_write(g, "i_");
					cgen_write(g, "]");
				}
				cgen_write(g, "; ");
				cgen_type_pre(g, &fo->type);
				cgen_write(g, " ");
				cgen_ident(g, fo->value);
				cgen_type_post(g, &fo->type);
				cgen_write(g, "; ");
				if (uses_ptr) {
					cgen_ident(g, fo->value);
					cgen_write(g, " = p_;");
					cgen_nl(g);
				} else {
					Expression set_expr;
					set_expr.kind = EXPR_IDENT;
					set_expr.ident = fo->value;
					set_expr.type = fo->type;
					set_expr.flags = EXPR_FOUND_TYPE;
				
					cgen_set(g, &set_expr, NULL, NULL, "(*p_)");
				}
			}
		}
		cgen_block(g, &fo->body, ret_name, CGEN_BLOCK_NOBRACES);
		cgen_write(g, "}}");
	} break;
	case EXPR_BLOCK:
		e->cgen.id = id;
		cgen_block(g, e->block, ret_name, 0);
		break;
	case EXPR_CALL: {
		cgen_expr_pre(g, e->call.fn);
	    size_t i = 0;
		Constness *constness = e->call.fn->type.fn.constness;
		size_t nparams = arr_len(e->call.fn->type.fn.types)-1;
		arr_foreach(e->call.arg_exprs, Expression, arg) {
			if (!constness || !arg_is_const(arg, constness[i])) {
				cgen_arg_pre(g, arg);
			}
			if (i < nparams-1) /* necessary for varargs */
				++i;
		}
		if (e->type.kind == TYPE_TUPLE) {
			Type *t = &e->type;
			size_t ntypes = arr_len(t->tuple);
			IdentID *ids = err_malloc(ntypes * sizeof *ids);
			for (i = 0; i < ntypes; ++i) {
				ids[i] = ++g->ident_counter;
				cgen_type_pre(g, &t->tuple[i]);
				cgen_write(g, " ");
				cgen_ident_id(g, ids[i]);
				cgen_type_post(g, &t->tuple[i]);
				cgen_write(g, "; ");
			}
		    cgen_expr(g, e->call.fn);
			if (e->call.instance) {
				cgen_fn_instance_number(g, e->call.instance->fn->instance_id);
			}
			cgen_write(g, "(");
			bool any_args = false;
			i = 0;
			arr_foreach(e->call.arg_exprs, Expression, arg) {
				if (!constness || !arg_is_const(arg, constness[i])) {
					if (any_args) cgen_write(g, ", ");
					any_args = true;
					cgen_arg(g, arg);
				}
				++i;
			}
			for (i = 0; i < ntypes; ++i) {
				if (any_args) cgen_write(g, ", ");
				any_args = true;
				cgen_write(g, "&");
				cgen_ident_id(g, ids[i]);
			}
			cgen_write(g, ");");
		} else if (cgen_uses_ptr(&e->type)) {
			e->cgen.id = id = ++g->ident_counter;
			cgen_type_pre(g, &e->type);
			cgen_write(g, " ");
			cgen_ident_id(g, id);
			cgen_type_post(g, &e->type);
			cgen_write(g, ";"); cgen_nl(g);
			cgen_expr(g, e->call.fn);
			if (e->call.instance) {
				cgen_fn_instance_number(g, e->call.instance->fn->instance_id);
			}
			cgen_write(g, "(");
			bool any_args = false;
			i = 0;
			arr_foreach(e->call.arg_exprs, Expression, arg) {
				if (!constness || !arg_is_const(arg, constness[i])) {
					if (any_args) cgen_write(g, ", ");
					any_args = true;
					cgen_arg(g, arg);
				}
				++i;
			}
			if (any_args) {
				cgen_write(g, ", ");
			}
			cgen_write(g, "&");
			cgen_ident_id(g, e->cgen.id);
			cgen_write(g, ");");
			cgen_nl(g);
		}
	} break;
	case EXPR_UNARY_OP:
		cgen_expr_pre(g, e->unary.of);
		break;
	case EXPR_BINARY_OP:
		cgen_expr_pre(g, e->binary.lhs);
		if (e->binary.op != BINARY_DOT)
			cgen_expr_pre(g, e->binary.rhs);
		break;
	case EXPR_CAST:
		cgen_expr_pre(g, e->cast.expr);
		break;
	case EXPR_SLICE: {
		SliceExpr *s = &e->slice;
		IdentID s_id = e->slice.c.id = ++g->ident_counter;
		IdentID from_id = ++g->ident_counter;
		cgen_expr_pre(g, s->of);
		if (s->from) cgen_expr_pre(g, s->from);
		if (s->to) cgen_expr_pre(g, s->to);
		cgen_write(g, "slice_ ");
		cgen_ident_id(g, s_id);
		cgen_write(g, "; { slice_ of__ = ");
		if (s->of->type.kind == TYPE_SLICE) {
			cgen_expr(g, s->of);
		} else {
			assert(s->of->type.kind == TYPE_ARR);
			cgen_write(g, "mkslice_(");
			cgen_expr(g, s->of);
			cgen_write(g, ", " U64_FMT, s->of->type.arr.n);
			cgen_write(g, ")");
		}
		cgen_write(g, "; i64 ");
		cgen_ident_id(g, from_id);
		cgen_write(g, " = ");
		if (s->from) {
			cgen_expr(g, s->from);
		} else {
			cgen_write(g, "0");
		}
		cgen_write(g, "; ");
		cgen_ident_id(g, s_id);
		cgen_write(g, ".data = (");
		cgen_type_pre(g, e->type.slice);
		cgen_write(g, "(*)");
		cgen_type_post(g, e->type.slice);
		cgen_write(g, ")(of__");
		cgen_write(g, ".data");
		cgen_write(g, ") + ");
		cgen_ident_id(g, from_id);
		cgen_write(g, "; ");
		cgen_ident_id(g, s_id);
		cgen_write(g, ".n = ");
		if (s->to) {
			cgen_expr(g, s->to);
		} else {
			cgen_write(g, "of__.n");
		}
		cgen_write(g, " - ");
		cgen_ident_id(g, from_id);
		cgen_write(g, "; }");
		cgen_nl(g);
	} break;
	case EXPR_NEW:
		if (e->new.n) cgen_expr_pre(g, e->new.n);
		break;
	case EXPR_VAL:
		/* TODO: don't make a variable for this if it's not needed */
		if (type_is_compileonly(&e->type))
			break;
		if (!cgen_is_type_simple(&e->type)) {
			cgen_val_pre(g, e->val, &e->type);
			cgen_type_pre(g, &e->type);
			e->cgen.id = ++g->ident_counter;
			cgen_write(g, " ");
			cgen_ident_id(g, e->cgen.id);
			cgen_type_post(g, &e->type);
			cgen_write(g, " = ");
			cgen_val(g, e->val, &e->type);
			cgen_writeln(g, ";");
		}
		break;
	case EXPR_TUPLE:
		arr_foreach(e->tuple, Expression, x)
			cgen_expr_pre(g, x);
		break;
	case EXPR_BUILTIN:
		switch (e->builtin.which.val) {
		case BUILTIN_STDOUT:
			cgen_write(g, "extern void *stdout;");
			cgen_nl(g);
			break;
		case BUILTIN_STDERR:
			cgen_write(g, "extern void *stderr;");
			cgen_nl(g);
			break;
		case BUILTIN_STDIN:
			cgen_write(g, "extern void *stdin;");
			cgen_nl(g);
			break;
	    default:
			break;
		}
		break;
	case EXPR_LITERAL_INT:
	case EXPR_LITERAL_FLOAT:
	case EXPR_LITERAL_BOOL:
	case EXPR_LITERAL_CHAR:
	case EXPR_LITERAL_STR:
	case EXPR_IDENT:
	case EXPR_FN:
	case EXPR_C:
	case EXPR_TYPE:
	case EXPR_NMS:
		break;
	}
}

static void cgen_expr(CGenerator *g, Expression *e) {
	assert(e->flags & EXPR_FOUND_TYPE);
	switch (e->kind) {
	case EXPR_LITERAL_FLOAT:
		cgen_write(g, "%.16Lf", (long double)e->floatl);
		break;
	case EXPR_LITERAL_INT:
		cgen_write(g, U64_FMT, e->intl);
		break;
	case EXPR_LITERAL_STR: {
		char *p = e->strl.str;
		cgen_write(g, "mkslice_(\"");
		for (size_t i = 0; i < e->strl.len; ++i, ++p) {
			if (isprint(*p) && *p != '"')
				cgen_write(g, "%c", *p);
			else
				cgen_write(g, "\\x%02x", *p);
		}
		cgen_write(g, "\", %lu)", (unsigned long)e->strl.len);
	} break;
	case EXPR_LITERAL_BOOL:
		cgen_write(g, e->booll ? "true" : "false");
		break;
	case EXPR_LITERAL_CHAR:
		cgen_write(g, "((char)%d)", e->charl);
		break;
	case EXPR_IDENT: {
		bool handled = false;
		if (e->type.kind == TYPE_FN) {
			/* generate the right function name, because it might be anonymous */
		    Identifier i = e->ident;
			if (i->decl_kind == IDECL_DECL) {
				Declaration *d = i->decl;
				if (d->flags & DECL_IS_CONST) {
					int index = decl_ident_index(d, i);
					Value fn_val = *decl_val_at_index(d, index);
					FnExpr *fn = fn_val.fn;
					Expression fn_expr;
					/* TODO: is this all really necessary? */
					
					fn_expr.kind = EXPR_FN;
					fn_expr.fn = allocr_malloc(g->allocr, sizeof *fn_expr.fn);
					*fn_expr.fn = *fn;
					fn_expr.flags = EXPR_FOUND_TYPE;
					fn_expr.type = *decl_type_at_index(d, index);
					
					cgen_expr(g, &fn_expr);
					handled = true;
				}
			}
		}
		if (!handled) {
			cgen_ident(g, e->ident);
		}
	} break;
	case EXPR_BINARY_OP: {
		const char *s = "";
		Expression *lhs = e->binary.lhs, *rhs = e->binary.rhs;
		bool handled = false;
		switch (e->binary.op) {
		case BINARY_SUB:
			s = "-"; break;
		case BINARY_ADD:
			s = "+"; break;
		case BINARY_MUL:
			s = "*"; break;
		case BINARY_DIV:
			s = "/"; break;
		case BINARY_MOD:
			s = "%"; break;
		case BINARY_SET: 
			cgen_set(g, lhs, NULL, rhs, NULL);
			handled = true;
			break;
		case BINARY_GT:
			s = ">"; break;
		case BINARY_LT:
			s = "<"; break;
		case BINARY_GE:
			s = ">="; break;
		case BINARY_LE:
			s = "<="; break;
		case BINARY_EQ:
			s = "=="; break;
		case BINARY_NE:
			s = "!="; break;
		case BINARY_SET_ADD:
			s = "+="; break;
		case BINARY_SET_SUB:
			s = "-="; break;
		case BINARY_SET_MUL:
			s = "*="; break;
		case BINARY_SET_DIV:
			s = "/="; break;
		case BINARY_SET_MOD:
			s = "%="; break;
		case BINARY_AT_INDEX: {
			Type *lhs_type = &lhs->type;
			cgen_write(g, "(");
			switch (lhs_type->kind) {
			case TYPE_ARR:
				cgen_expr(g, lhs);
				cgen_write(g, "[");
				cgen_expr(g, rhs);
				cgen_write(g, "]");
				break;
			case TYPE_SLICE:
				cgen_write(g, "((");
				cgen_type_pre(g, &e->type);
				cgen_write(g, "(*)");
				cgen_type_post(g, &e->type);
				cgen_write(g, ")(");
				cgen_expr(g, lhs);
				cgen_write(g, ".data))[");
				cgen_expr(g, rhs);
				cgen_write(g, "]");
				break;
			case TYPE_BUILTIN:
			    if (lhs_type->builtin == BUILTIN_VARARGS) {
					assert(lhs->kind == EXPR_IDENT);
					assert(rhs->kind == EXPR_VAL);
					assert(type_is_builtin(&rhs->type, BUILTIN_I64));
					I64 i = rhs->val.i64;
					cgen_ident(g, lhs->ident);
					cgen_write(g, I64_FMT "_", i);
				} else assert(0);
				break;
			default:
				assert(0);
				break;
			}
			cgen_write(g, ")");
			handled = true;
		} break;
		case BINARY_DOT: {
			Type *struct_type = &lhs->type;
			if (struct_type->kind == TYPE_PTR) struct_type = struct_type->ptr;
			if (struct_type->kind == TYPE_STRUCT) {
				cgen_write(g, "(");
				cgen_expr(g, lhs);
				bool is_ptr = lhs->type.kind == TYPE_PTR;
				cgen_write(g, is_ptr ? "->" :".");
				cgen_ident_simple(g, e->binary.dot.field->name);
				cgen_write(g, ")");
			} else {
				assert(type_is_builtin(struct_type, BUILTIN_NMS));
				char *prefix = lhs->val.nms->c.prefix;
				cgen_write(g, "%s", prefix);
				cgen_ident_simple(g, rhs->ident);
			}
			handled = true;
		} break;
		}
		if (handled) break;
		cgen_write(g, "(");
		cgen_expr(g, lhs);
		cgen_write(g, "%s", s);
		cgen_expr(g, rhs);
		cgen_write(g, ")");
	} break;
	case EXPR_UNARY_OP: {
		const char *s = "";
		bool handled = false;
		Type *of_type = &e->unary.of->type;
		switch (e->unary.op) {
		case UNARY_MINUS:
			s = "-"; break;
		case UNARY_DEREF:
			s = "*"; break;
		case UNARY_ADDRESS:
			s = "&"; break;
		case UNARY_NOT:
			s = "!"; break;
		case UNARY_DEL:
			cgen_write(g, "free_(");
			cgen_expr(g, e->unary.of);
			if (of_type->kind == TYPE_SLICE)
				cgen_write(g, ".data");
			cgen_write(g, ")");
			handled = true;
			break;
		case UNARY_LEN: {
			bool is_ptr = of_type->kind == TYPE_PTR;
			if (is_ptr) {
				of_type = of_type->ptr;
			}
			switch (of_type->kind) {
			case TYPE_SLICE:
				cgen_expr(g, e->unary.of);
				cgen_write(g, "%sn", is_ptr ? "->" : ".");
				break;
			case TYPE_ARR:
				cgen_write(g, "%lu", (unsigned long)of_type->arr.n);
				break;
			default: assert(0); break;
			}
			handled = true;
		} break;
		case UNARY_TYPEOF:
		case UNARY_DSIZEOF:
		case UNARY_DALIGNOF:
			assert(0);
			return;
		}
		if (handled) break;
		cgen_write(g, "(");
		cgen_write(g, "%s", s);
		cgen_expr(g, e->unary.of);
		cgen_write(g, ")");
	} break;
	case EXPR_NEW: {
		if (e->new.n) {
			cgen_write(g, "mkslice_(ecalloc_(");
			cgen_expr(g, e->new.n);
			cgen_write(g, ", (i64)sizeof(");
			cgen_type_pre(g, &e->new.type);
			cgen_type_post(g, &e->new.type);
			cgen_write(g, ")), ");
			cgen_expr(g, e->new.n);
			cgen_write(g, ")");
		} else {
			Type *t = &e->new.type;
			cgen_write(g, "((");
			cgen_type_pre(g, &e->type);
			cgen_type_post(g, &e->type);
			cgen_write(g, ")ecalloc_(1, sizeof(");
			cgen_type_pre(g, t);
			cgen_type_post(g, t);
			cgen_write(g, ")))");
		}
	} break;
	case EXPR_IF:
	case EXPR_WHILE:
	case EXPR_BLOCK:
	case EXPR_FOR:
		if (e->type.kind != TYPE_VOID)
			cgen_ident_id(g, e->cgen.id);
		break;
	case EXPR_CALL:
		if (e->type.kind == TYPE_TUPLE) {
			/* the only situation in which this could happen is if the return value doesn't matter */
		} else if (cgen_uses_ptr(&e->type)) {
			cgen_ident_id(g, e->cgen.id);
		} else {
			FnType *fn_type = &e->call.fn->type.fn;
			cgen_write(g, "(");
			cgen_expr(g, e->call.fn);
			if (e->call.instance) {
				cgen_fn_instance_number(g, e->call.instance->fn->instance_id);
			}
			cgen_write(g, "(");
			bool first_arg = true;
		    size_t i = 0;
			size_t nparams = arr_len(fn_type->types)-1;
			arr_foreach(e->call.arg_exprs, Expression, arg) {
				if (!fn_type->constness || !arg_is_const(arg, fn_type->constness[i])) {
					if (!first_arg)
						cgen_write(g, ", ");
					first_arg = false;
					cgen_arg(g, arg);
				}
				if (i < nparams-1)
					++i;
			}
			cgen_write(g, "))");
		}
		break;
	case EXPR_C: {
		Expression *code = e->c.code;
		assert(code->kind == EXPR_VAL);
		cgen_indent(g);
		fwrite(code->val.slice.data, 1, (size_t)code->val.slice.n, cgen_writing_to(g));
	} break;
	case EXPR_BUILTIN:
		switch (e->builtin.which.val) {
		case BUILTIN_STDOUT:
			cgen_write(g, "stdout");
			break;
		case BUILTIN_STDERR:
			cgen_write(g, "stderr");
			break;
		case BUILTIN_STDIN:
			cgen_write(g, "stdin");
			break;
		case BUILTIN_COMPILING:
			cgen_write(g, "false");
			break;
		case BUILTIN_SIZEOF_SHORT:
		case BUILTIN_SIZEOF_INT:
		case BUILTIN_SIZEOF_LONG:
		case BUILTIN_SIZEOF_LONG_LONG:
		case BUILTIN_SIZEOF_FLOAT:
		case BUILTIN_SIZEOF_DOUBLE:
		case BUILTIN_SIZEOF_LONG_DOUBLE:
		case BUILTIN_TSIZEOF_SHORT:
		case BUILTIN_TSIZEOF_INT:
		case BUILTIN_TSIZEOF_LONG:
		case BUILTIN_TSIZEOF_LONG_LONG:
		case BUILTIN_TSIZEOF_FLOAT:
		case BUILTIN_TSIZEOF_DOUBLE:
		case BUILTIN_TSIZEOF_LONG_DOUBLE:
		case BUILTIN_SIZEOF_SIZE_T:
		case BUILTIN_TSIZEOF_SIZE_T: {
			Value val = get_builtin_val(e->builtin.which.val);
			cgen_write(g, I64_FMT, val.i64);
		} break;
		}
		break;
	case EXPR_CAST: {
		Type *from = &e->cast.expr->type;
		Type *to = &e->cast.type;
		if (to->kind == TYPE_ARR) {
			/* can't cast to array type */
			cgen_expr(g, e->cast.expr);
		} else {
			cgen_write(g, "((");
			cgen_type_pre(g, to);
			cgen_type_post(g, to);
			cgen_write(g, ")(");
			cgen_expr(g, e->cast.expr);
			cgen_write(g, ")");
			if (from->kind == TYPE_SLICE /* casting from a slice to a non-slice */
				&& to->kind != TYPE_SLICE) 
				cgen_write(g, ".data");
			cgen_write(g, ")");
		}
	} break;
	case EXPR_TUPLE:
		/* the only time this should happen is if you're stating
		   a tuple, e.g. 3, 5;, but we've errored about that before
		*/
	case EXPR_TYPE:
		assert(0);
		break;
	case EXPR_FN: {
		FnExpr *f = e->fn;
		cgen_fn_name(g, f);
	} break;
	case EXPR_SLICE:
		cgen_ident_id(g, e->slice.c.id);
		break;
	case EXPR_VAL: {
		Type *t = &e->type;
		if (cgen_is_type_simple(t)) {
			cgen_val(g, e->val, t);
		} else {
			cgen_ident_id(g, e->cgen.id);
		}
	} break;
	case EXPR_NMS:
		break;
	}
}

/*
  ret_name = variable to store block return value in; NULL for none. NOTE:
  functions always call with NULL as ret_name, even if they use out params, for now
  at least. 
*/
static void cgen_block(CGenerator *g, Block *b, const char *ret_name, U16 flags) {
	Block *prev_block = g->block;
	g->block = b;
	
	if (!(flags & CGEN_BLOCK_NOBRACES)) {
		cgen_write(g, "{");
		cgen_nl(g);
	}
	arr_foreach(b->stmts, Statement, s)
		cgen_stmt(g, s);
	if (b->ret_expr && ret_name) {
		cgen_expr_pre(g, b->ret_expr);
		if (b->ret_expr->type.kind == TYPE_TUPLE) {
			cgen_set_tuple(g, NULL, NULL, ret_name, b->ret_expr);
		} else {
			cgen_set(g, NULL, ret_name, b->ret_expr, NULL);
		}
		cgen_nl(g);
	}
	if (!(flags & CGEN_BLOCK_NOBRACES))
		cgen_write(g, "}");
	g->block = prev_block;
}

static void cgen_zero_value(CGenerator *g, Type *t) {
	assert(t->flags & TYPE_IS_RESOLVED);
	switch (t->kind) {
	case TYPE_BUILTIN:
		cgen_write(g, "0");
		break;
	case TYPE_PTR:
	case TYPE_FN:
		cgen_write(g, "NULL");
		break;
	case TYPE_SLICE:
		cgen_write(g, "{NULL, 0}");
		break;
	case TYPE_ARR:
	case TYPE_STRUCT:
		cgen_write(g, "{0}");
		break;
	case TYPE_VOID:
	case TYPE_UNKNOWN:
	case TYPE_TUPLE:
	case TYPE_EXPR:
		assert(0);
		break;
	}
}

/* pass NULL for compile_time_args if there are no compile time arguments.
compile_time_args is needed because we can't determine which_are_const
from just f.
 */
static void cgen_fn(CGenerator *g, FnExpr *f, Value *compile_time_args) {
	if (f->flags & FN_EXPR_FOREIGN)
		return; /* handled by decls_cgen */
	/* see also cgen_defs_expr */
	FnExpr *prev_fn = g->fn;
	U64 which_are_const = compile_time_args ? compile_time_args->u64 : 0;
	if (!cgen_should_gen_fn(f))
		return;
	cgen_fn_header(g, f, which_are_const);
	g->fn = f;
	cgen_write(g, " {");
	cgen_nl(g);
	if (compile_time_args) {
		++compile_time_args; /* move past which_are_const */
		int semi_const_idx = 0;
		arr_foreach(f->params, Declaration, param) {
			if ((param->flags & DECL_IS_CONST)
				|| ((param->flags & DECL_SEMI_CONST)
					&& (which_are_const & (((U64)1) << semi_const_idx++)))) {
				int i = 0;
				if (type_is_builtin(&param->type, BUILTIN_VARARGS)) {
					VarArg *vararg = param->val.varargs;
					size_t nvarargs = arr_len(vararg);
					for (size_t v = 0; v < nvarargs; ++v, ++vararg) {
						Type *type = vararg->type;
						Value arg = vararg->val;
						if (!type_is_compileonly(type)) {
							cgen_val_pre(g, arg, type);
							cgen_type_pre(g, type);
							cgen_write(g, " const ");
							assert(arr_len(param->idents) == 1);
							cgen_ident(g, param->idents[0]);
							cgen_write(g, "%lu_", (unsigned long)v);
							cgen_type_post(g, type);
							cgen_write(g, " = ");
							cgen_val(g, arg, type);
							cgen_writeln(g, ";");
						}
					}
				} else {
					arr_foreach(param->idents, Identifier, ident) {
						Type *type = decl_type_at_index(param, i);
						Value arg = *decl_val_at_index(param, i);
						if (!type_is_compileonly(type)) {
							cgen_val_pre(g, arg, type);
							cgen_type_pre(g, type);
							cgen_write(g, " const ");
							cgen_ident(g, *ident);
							cgen_type_post(g, type);
							cgen_write(g, " = ");
							cgen_val(g, arg, type);
							cgen_writeln(g, ";");
						}
						++i;
					}
				}
			}
		}
					
	}
	/* retdecls need to be after compile time arguments to allow fn(x::int) y := x */
	arr_foreach(f->ret_decls, Declaration, d) {
		cgen_decl(g, d);
	}
	
	cgen_block(g, &f->body, NULL, CGEN_BLOCK_NOBRACES);
	if (f->ret_decls) {
		cgen_ret(g, NULL);
	} else if (f->body.ret_expr) {
		cgen_ret(g, f->body.ret_expr);
	}
	
	cgen_write(g, "}");
	cgen_nl(g);
	g->fn = prev_fn;
	cgen_nl(g);
	cgen_nl(g);
}

static void cgen_decl(CGenerator *g, Declaration *d) {
	if (g->block == NULL && g->fn == NULL)
		return; /* already dealt with */
	int has_expr = d->flags & DECL_HAS_EXPR;
	if (cgen_fn_is_direct(g, d))
		return; /* dealt with in cgen_defs_ */
	if (d->flags & DECL_FOUND_VAL) {
		/* declarations where we use a value */
		for (int idx = 0, nidents = (int)arr_len(d->idents); idx < nidents; ++idx) {
			Identifier i = d->idents[idx];
			Type *type = decl_type_at_index(d, idx);
			if (type_is_compileonly(&d->type)) {
			    continue;
			}
			Value *val = decl_val_at_index(d, idx);
			if (has_expr) {
				cgen_val_pre(g, *val, type);
			}
		    cgen_type_pre(g, type);
			cgen_write(g, " ");
			cgen_ident(g, i);
		    cgen_type_post(g, type);
			if (has_expr) {
				cgen_write(g, " = ");
				cgen_val(g, *val, type);
			} else {
				cgen_write(g, " = ");
				cgen_zero_value(g, type);
			}
			cgen_write(g, ";");
			cgen_nl(g);
		}
	} else {
		/* declarations where we use an expression */
		int nidents = (int)arr_len(d->idents);
		for (int idx = 0; idx < nidents; ++idx) {
			Identifier i = d->idents[idx];
			if (ident_eq_str(i, "_")) continue;
			Type *type = decl_type_at_index(d, idx);
		    cgen_type_pre(g, type);
			cgen_write(g, " ");
			cgen_ident(g, i);
		    cgen_type_post(g, type);
			if (!has_expr) {
				cgen_write(g, " = ");
				cgen_zero_value(g, type);
			}
				
			cgen_write(g, "; ");
		}
		if (has_expr) {
			assert((g->block || g->fn) && !(d->flags & DECL_IS_CONST));
			if (d->expr.type.kind == TYPE_TUPLE) {
				cgen_set_tuple(g, NULL, d->idents, NULL, &d->expr);
			} else {
				cgen_expr_pre(g, &d->expr);
				if (nidents > 1) {
					/* set expr__ first to make sure side effects don't happen twice */
					cgen_write(g, "{");
					cgen_nl(g);
					cgen_type_pre(g, &d->type);
					cgen_write(g, " expr_");
				    cgen_type_post(g, &d->type);
					cgen_write(g, "; ");
					cgen_set(g, NULL, "expr_", &d->expr, NULL);
				
					arr_foreach(d->idents, Identifier, i) {
						Expression e;
						e.flags = EXPR_FOUND_TYPE;
						e.kind = EXPR_IDENT;
						e.type = d->type;
						e.ident = *i;
						cgen_set(g, &e, NULL, NULL, "expr_");
					}
					cgen_write(g, "}");
				} else {
					/* set it directly */
					Expression e = {0};
					e.kind = EXPR_IDENT;
					e.type = d->type;
					e.flags = EXPR_FOUND_TYPE;
					e.ident = d->idents[0];
					cgen_set(g, &e, NULL, &d->expr, NULL);
				}
			}
		}
		cgen_nl(g);
	}
}

static void cgen_ret(CGenerator *g, Expression *ret) {
	FnExpr *f = g->fn;
	if (f->ret_decls) {
		assert(!ret);
		if (f->ret_type.kind == TYPE_TUPLE) {
			Expression ret_expr = {0};
			ret_expr.flags = EXPR_FOUND_TYPE;
			ret_expr.type = f->ret_type;
			ret_expr.kind = EXPR_TUPLE;
			ret_expr.tuple = NULL;
			arr_set_len(&ret_expr.tuple, arr_len(f->ret_type.tuple));
			int idx = 0;
			arr_foreach(f->ret_decls, Declaration, d) {
				arr_foreach(d->idents, Identifier, ident) {
					Expression *e = &ret_expr.tuple[idx];
					e->flags = EXPR_FOUND_TYPE;
					e->type = f->ret_type.tuple[idx];
					e->kind = EXPR_IDENT;
					e->ident = *ident;
					++idx;
				}
			}
		    cgen_set_tuple(g, NULL, NULL, "*ret__", &ret_expr);
			arr_clear(&ret_expr.tuple);
		} else if (cgen_uses_ptr(&f->ret_type)) {
			Expression ret_expr = {0};
			ret_expr.flags = EXPR_FOUND_TYPE;
			ret_expr.type = f->ret_type;
			ret_expr.kind = EXPR_IDENT;
			ret_expr.ident = f->ret_decls[0].idents[0];
			cgen_set(g, NULL, "*ret__", &ret_expr, NULL);
			cgen_writeln(g, ";");
			cgen_writeln(g, "return;");
		} else {
			cgen_write(g, "return ");
			cgen_ident(g, f->ret_decls[0].idents[0]);
			cgen_writeln(g, ";");
		}
		return;
	}
	if (ret) {
		assert(type_eq(&f->ret_type, &ret->type));
		cgen_expr_pre(g, ret);
	}
	if (!ret) {
		cgen_write(g, "return");
	} else if (cgen_uses_ptr(&f->ret_type)) {
		if (f->ret_type.kind == TYPE_TUPLE) {
			cgen_set_tuple(g, NULL, NULL, "*ret__", ret);
		} else {
		    cgen_set(g, NULL, "*ret__", ret, NULL);
		}
		cgen_write(g, " return");
	} else {
		cgen_write(g, "return ");
	    cgen_expr(g, ret);
	}
	cgen_writeln(g, ";");
}

static void cgen_stmt(CGenerator *g, Statement *s) {

#ifdef CGEN_EMIT_LINE_NUMBER_COMMENTS
	/* TODO: add compiler option for this */
	cgen_write(g, "/* %s:%d */", s->where.ctx->filename, s->where.line);
#endif
	switch (s->kind) {
	case STMT_DECL:
		cgen_decl(g, s->decl);
		break;
	case STMT_EXPR:
		if ((g->block != NULL || s->expr.kind == EXPR_C) && !type_is_compileonly(&s->expr.type)) {
		    cgen_expr_pre(g, &s->expr);
			cgen_expr(g, &s->expr);
			if (s->expr.kind != EXPR_C)
				cgen_writeln(g, ";");
		}
		break;
	case STMT_RET: {
		unsigned has_expr = s->ret.flags & RET_HAS_EXPR;
		cgen_ret(g, has_expr ? &s->ret.expr : NULL);
	} break;
	case STMT_INCLUDE:
		if (s->inc.inc_file && (s->inc.inc_file->flags & INC_FILE_CGEND)){
			/* already generated */
		} else {
			if (s->inc.inc_file) s->inc.inc_file->flags |= INC_FILE_CGEND;
			arr_foreach(s->inc.stmts, Statement, sub)
				cgen_stmt(g, sub);
	    }
	    break;
	}
}

static void cgen_defs_fn(CGenerator *g, FnExpr *f) {
	if (fn_has_instances(f)) {
		HashTable *instances = f->instances;
		/* generate each instance */
		Instance **is = instances->data;
		for (U64 i = 0; i < instances->cap; ++i) {
			if (instances->occupied[i]) {
				/* generate this instance */
				cgen_fn(g, is[i]->fn, is[i]->val.tuple);
			}
		}
	} else {
		cgen_fn(g, f, NULL);
	}
}

static void cgen_defs_expr(CGenerator *g, Expression *e) {
	if (e->kind == EXPR_FN) {
	    cgen_defs_fn(g, e->fn);
	}
	cgen_recurse_subexprs(g, e, cgen_defs_expr, cgen_defs_block, cgen_defs_decl);
}

static void cgen_defs_decl(CGenerator *g, Declaration *d) {
	if (d->flags & DECL_HAS_EXPR) {
		cgen_defs_expr(g, &d->expr);
	}
}


static void cgen_defs_stmt(CGenerator *g, Statement *s) {
	switch (s->kind) {
	case STMT_DECL:
		cgen_defs_decl(g, s->decl);
		break;
	case STMT_EXPR:
		cgen_defs_expr(g, &s->expr);
		break;
	case STMT_RET:
		if (s->ret.flags & RET_HAS_EXPR)
			cgen_defs_expr(g, &s->ret.expr);
		break;
	case STMT_INCLUDE:
		if (s->inc.inc_file && (s->inc.inc_file->flags & INC_FILE_CGEND_DEFS)) {
			/* already generated */
		} else {
		    if (s->inc.inc_file) s->inc.inc_file->flags |= INC_FILE_CGEND_DEFS;
			arr_foreach(s->inc.stmts, Statement, sub)
				cgen_defs_stmt(g, sub);
		}
		break;
	}
}

static void cgen_defs_block(CGenerator *g, Block *b) {
	/* 
	   NOTE: since we exit as soon as there's an error for cgen, we don't need to make sure we
	   set g->block to the previous block if there's an error
	*/
	Block *prev_block = g->block;
	g->block = b;
	arr_foreach(b->stmts, Statement, s) {
		cgen_defs_stmt(g, s);
	}
	if (b->ret_expr) cgen_defs_expr(g, b->ret_expr);
	g->block = prev_block;
}

static void cgen_file(CGenerator *g, ParsedFile *f) {
	g->block = NULL;
	g->nms = NULL;
	g->fn = NULL;
	g->file = f;

	cgen_write(g, "#include <stdint.h>\n"
			   "#include <stddef.h>\n"
			   "typedef int8_t i8;\n"
			   "typedef int16_t i16;\n"
			   "typedef int32_t i32;\n"
			   "typedef int64_t i64;\n"
			   "typedef uint8_t u8;\n"
			   "typedef uint16_t u16;\n"
			   "typedef uint32_t u32;\n"
			   "typedef uint64_t u64;\n"
			   "typedef float f32;\n"
			   "typedef double f64;\n"
			   "typedef u8 bool;\n"
			   "typedef struct { void *data; i64 n; } slice_;\n"
			   "#define false ((bool)0)\n"
			   "#define true ((bool)1)\n"
			   "static slice_ mkslice_(void *data, i64 n) { slice_ ret; ret.data = data; ret.n = n; return ret; }\n"
			   "static void free_(void *data) { extern void free(void *data); free(data); }\n" /* don't introduce free to global namespace */
			   "static void *ecalloc_(size_t n, size_t sz) { extern void *calloc(size_t n, size_t size); extern void abort(void); extern int printf(const char *fmt, ...); void *ret = calloc(n, sz); if (n && sz && !ret) { printf(\"Out of memory.\\n\"); abort(); } return ret; }\n\n\n");

	cgen_sdecls_file(g, f);
	cgen_decls_file(g, f);
	cgen_write(g, "/* code */\n");
	cgen_write(g, "int main() {\n\tmain_();\n\treturn 0;\n}\n\n");
	arr_foreach(f->stmts, Statement, s) {
		cgen_defs_stmt(g, s);
	}

	arr_foreach(f->stmts, Statement, s) {
		cgen_stmt(g, s);
	}
}