add trailing closures

+ Useful for guard statements, not entirely sure about the final syntax
  but at least they're possible

6 files changed, 94 insertions, 18 deletions

diff --git a/examples/fib.fwd b/examples/fib.fwd
index 44ced4a..be2b63f 100644
--- a/examples/fib.fwd
+++ b/examples/fib.fwd
@@ -14,6 +14,9 @@ fib(int n, (int) res)
 	}
 }
 
+/* 'extern' println */
+fwd_println(int n);
+
 main()
 {
 	fib(6) => int n;
diff --git a/examples/guard.fwd b/examples/guard.fwd
new file mode 100644
index 0000000..6af570d
--- /dev/null
+++ b/examples/guard.fwd
@@ -0,0 +1,33 @@
+/* 'any' doesn't actually exist but at the moment I'm not checking types so as
+ * long as there's some type identifier here the compiler will not complain,
+ * will eventually have to fix */
+fwd_println(any a);
+
+guard(bool cond, () err, () ok)
+{
+	if cond {
+		err();
+	} else {
+		ok();
+	}
+}
+
+try_print_one(int a)
+{
+	guard(a < 1) => {
+		fwd_println("smaller than 1");
+	} => ;
+
+	guard(a > 1) => {
+		fwd_println("larger than 1");
+	} => ;
+
+	fwd_println(a);
+}
+
+main()
+{
+	try_print_one(0);
+	try_print_one(1);
+	try_print_one(2);
+}
diff --git a/examples/uniq.fwd b/examples/uniq.fwd
index fa7504a..5945d65 100644
--- a/examples/uniq.fwd
+++ b/examples/uniq.fwd
@@ -1,5 +1,15 @@
 /* not entirely sure about the final syntax just yet but something like this */
 
+/* 'extern' functions (though some should probably be generic?) */
+fwd_getline(
+	(optional![string]) next);
+
+fwd_some(optional![string] o,
+	(string) next);
+
+fwd_insert(unordered_set![string] set, string line,
+	(unordered_set![string]) next);
+
 /* at some point I'll probably add in a type system as well, but for now let's
  * pretend we're static-dynamic (or dynamic at compiletime? dunno) */
 readlines(unordered_set![string] set, (unordered_set![string]) next)
@@ -19,6 +29,11 @@ readlines(unordered_set![string] set, (unordered_set![string]) next)
 	}
 }
 
+fwd_foreach(unordered_set![string] set,
+	(string) callback);
+
+fwd_println(string s);
+
 main()
 {
 	/* fwdlib.hpp uses namespace std, not good practice but allows us to do
diff --git a/lib/fwdlib.hpp b/lib/fwdlib.hpp
index 3efac61..5c52f65 100644
--- a/lib/fwdlib.hpp
+++ b/lib/fwdlib.hpp
@@ -10,23 +10,15 @@
 
 using namespace std;
 
-static void fwd_if(auto cond, auto ok, auto fail)
-{
-	if (cond)
-		ok();
-	else
-		fail();
-}
-
 static void fwd_getline(auto next)
 {
 	if (cin.eof())
-		next(optional<string>{});
+		return next(optional<string>{});
 
 	if (string line; getline(cin, line))
-		next(optional<string>{line});
+		return next(optional<string>{line});
 	else
-		next(optional<string>{});
+		return next(optional<string>{});
 }
 
 static void fwd_foreach(auto container, auto next)
@@ -38,15 +30,15 @@ static void fwd_foreach(auto container, auto next)
 static void fwd_some(auto option, auto ok, auto fail)
 {
 	if (option)
-		ok(std::move(option.value()));
+		return ok(std::move(option.value()));
 	else
-		fail();
+		return fail();
 }
 
 static void fwd_insert(auto container, auto elem, auto next)
 {
 	container.insert(std::move(elem));
-	next(std::move(container));
+	return next(std::move(container));
 }
 
 static void fwd_println(auto elem)
diff --git a/src/lower.c b/src/lower.c
index 35d16fe..4b9fae9 100644
--- a/src/lower.c
+++ b/src/lower.c
@@ -123,6 +123,11 @@ static int lower_type_construct(struct type *type)
 
 static int lower_type_callable(struct type *type)
 {
+	/* std::function has a slight overhead compared to just using auto here,
+	 * but auto doesn't play well with recursive templates like with our
+	 * fib.fwd example, so use std::function for now. Eventually I might
+	 * instead write a C backend or something to have more control over the
+	 * exact semantics, but for now this is good enough. */
 	printf("std::function<void(");
 
 	if (lower_types(tcallable_args(type)))
@@ -317,8 +322,10 @@ static int lower_if(struct state *state, struct ast *stmt)
 	if (lower_block(state, if_body(stmt)))
 		return -1;
 
-	if (!if_else(stmt))
+	if (!if_else(stmt)) {
+		printf("\n");
 		return 0;
+	}
 
 	printf(" else ");
 	if (lower_block(state, if_else(stmt)))
@@ -403,6 +410,11 @@ static int lower_closure(struct state *state, struct ast *closure)
 
 static int lower_proto(struct ast *proc)
 {
+	/* 'extern' functions should be provided to us by whatever framework the
+	 * user is using */
+	if (!proc_body(proc))
+		return 0;
+
 	if (strcmp("main", proc_id(proc)) == 0)
 		printf("int ");
 	else
@@ -419,6 +431,9 @@ static int lower_proto(struct ast *proc)
 
 static int lower_proc(struct ast *proc)
 {
+	if (!proc_body(proc))
+		return 0;
+
 	if (strcmp("main", proc_id(proc)) == 0)
 		printf("int ");
 	else
diff --git a/src/parser.y b/src/parser.y
index 97a700e..9f532b9 100644
--- a/src/parser.y
+++ b/src/parser.y
@@ -93,8 +93,8 @@
 %left "::"
 
 %nterm <node> top unit proc call closure var expr statement body
-%nterm <node> vars exprs statements closures
-%nterm <node> opt_vars opt_exprs opt_statements
+%nterm <node> vars exprs statements closures trailing_closure
+%nterm <node> opt_vars opt_exprs opt_statements opt_trailing_closure
 %nterm <node> rev_vars rev_exprs rev_closures rev_statements
 %nterm <node> let if unop binop construct
 
@@ -197,6 +197,9 @@ proc
 	: ID "(" opt_vars ")" body {
 		$$ = gen_proc($[ID], $[opt_vars], NULL, $[body], src_loc(@$));
 	}
+	| ID "(" opt_vars ")" ";" {
+		$$ = gen_proc($[ID], $[opt_vars], NULL, NULL, src_loc(@$));
+	}
 
 binop
 	: expr "+"  expr { $$ = gen_binop(AST_ADD, $1, $3, src_loc(@$));  }
@@ -276,8 +279,22 @@ rev_closures
 	: rev_closures closure { $$ = $2; $2->n = $1; }
 	| closure
 
+trailing_closure
+	: "=>" opt_vars ";" { $$ = gen_closure($[opt_vars], NULL, src_loc(@$));}
+
+opt_trailing_closure
+	: trailing_closure
+	| { $$ = NULL; }
+
 closures
-	: rev_closures { $$ = reverse_ast_list($1); }
+	: rev_closures opt_trailing_closure {
+		if ($[opt_trailing_closure]) {
+			$[opt_trailing_closure]->n = $[rev_closures];
+			$$ = reverse_ast_list($[opt_trailing_closure]);
+		} else {
+			$$ = reverse_ast_list($[rev_closures]);
+		}
+	}
 
 call
 	: expr "(" opt_exprs ")" ";" {
@@ -307,6 +324,7 @@ statement
 	: call
 	| let
 	| if
+	| body
 	| ";" { $$ = gen_empty(src_loc(@$)); }
 
 rev_statements