feat: enable_if

6 files changed, 69 insertions, 1 deletions

diff --git a/ast.c b/ast.c
index ed694f9..58cbaf5 100644
--- a/ast.c
+++ b/ast.c
@@ -79,6 +79,14 @@ struct Node* node_named(enum NodeKind kind, const struct Name* name, struct Node
     return node;
 }
 
+struct Node* node_block(enum NodeKind kind, struct Node* first, struct Node* body)
+{
+    struct Node* node = node_new(kind);
+    node->first = first;
+    node->body = body;
+    return node;
+}
+
 struct Node* node_append(struct Node* list, struct Node* node)
 {
     struct Node* last = list;
@@ -98,6 +106,7 @@ void node_free(struct Node* node)
     node_free(node->first);
     node_free(node->second);
     node_free(node->third);
+    node_free(node->body);
     node_free(node->next);
     free(node);
 }
diff --git a/ast.h b/ast.h
index aaa5f7a..4a5db15 100644
--- a/ast.h
+++ b/ast.h
@@ -33,6 +33,7 @@ enum NodeKind
     COND_LESS,
     STMT_DECLARE,
     STMT_UNDECLARE,
+    STMT_ENABLE_IF,
     STMT_EMIT,
     STMT_STATIC_ASSERT
 };
@@ -52,6 +53,7 @@ struct Node
     struct Node* first;
     struct Node* second;
     struct Node* third;
+    struct Node* body;
     struct Node* next;
 };
 
@@ -65,6 +67,7 @@ struct Node* node_binary(enum NodeKind kind, struct Node* first, struct Node* se
 struct Node* node_ternary(enum NodeKind kind, struct Node* first, struct Node* second,
                           struct Node* third);
 struct Node* node_named(enum NodeKind kind, const struct Name* name, struct Node* first);
+struct Node* node_block(enum NodeKind kind, struct Node* first, struct Node* body);
 
 struct Node* node_append(struct Node* list, struct Node* node);
 void node_free(struct Node* node);
diff --git a/eval.c b/eval.c
index cb967c2..3f27fa2 100644
--- a/eval.c
+++ b/eval.c
@@ -254,6 +254,18 @@ static enum RunStatus emit(struct Machine* machine, const struct Node* node)
     return RUN_DONE;
 }
 
+static enum RunStatus enable_if(struct Machine* machine, const struct Node* node)
+{
+    bool truth = false;
+    if (evaluate_condition(machine, node->first, &truth))
+        return RUN_FAILED;
+
+    if (!truth)
+        return RUN_DONE;
+
+    return execute(machine, node->body);
+}
+
 static enum RunStatus static_assert_statement(struct Machine* machine, const struct Node* node)
 {
     bool truth = false;
@@ -275,6 +287,7 @@ static enum RunStatus execute_one(struct Machine* machine, const struct Node* no
     {
         case STMT_DECLARE: return declare(machine, node);
         case STMT_UNDECLARE: return undeclare(machine, node);
+        case STMT_ENABLE_IF: return enable_if(machine, node);
         case STMT_EMIT: return emit(machine, node);
         case STMT_STATIC_ASSERT: return static_assert_statement(machine, node);
         default: break;
diff --git a/examples/enable_if.sfinae b/examples/enable_if.sfinae
new file mode 100644
index 0000000..ff7dacc
--- /dev/null
+++ b/examples/enable_if.sfinae
@@ -0,0 +1,22 @@
+// ::enable_if_t runs a ::sequence of statements when its condition holds
+// the statements inside are separated by commas and each one is still committed
+
+::enable_if_t<
+    ::is_same<::remove_cv_t<::int32_t>, ::int32_t>::value,
+    ::sequence<
+        ::declare<::name<'x'>, ::decltype(::difference<'C', 'A'>)>::commit,
+        ::emit<::decltype(::value_of<::name<'x'>>)>::commit
+    >
+>::commit;
+
+// this one never runs, so nothing is printed and nothing is asserted
+::enable_if_t<
+    ::false_type::value,
+    ::sequence<
+        ::static_assert<::false_type::value>::commit,
+        ::emit<::decltype(::difference<'Z', 'A'>)>::commit
+    >
+>::commit;
+
+// an empty sequence is allowed, for when you have nothing to say
+::enable_if_t<::true_type::value, ::sequence<>>::commit;
diff --git a/sfinae.l b/sfinae.l
index 17bf28e..0ab1eeb 100644
--- a/sfinae.l
+++ b/sfinae.l
@@ -37,6 +37,8 @@ static int fail(const char* message)
 "commit"                return TOK_COMMIT;
 "declare"               return TOK_DECLARE;
 "undeclare"             return TOK_UNDECLARE;
+"enable_if_t"           return TOK_ENABLE_IF;
+"sequence"              return TOK_SEQUENCE;
 "name"                  return TOK_NAME;
 "value_of"              return TOK_VALUE_OF;
 "void"                  return TOK_VOID;
diff --git a/sfinae.y b/sfinae.y
index 1acb4d0..f97147f 100644
--- a/sfinae.y
+++ b/sfinae.y
@@ -23,6 +23,8 @@ void yyerror(const char* message);
 %token TOK_COMMIT
 %token TOK_DECLARE
 %token TOK_UNDECLARE
+%token TOK_ENABLE_IF
+%token TOK_SEQUENCE
 %token TOK_NAME
 %token TOK_VALUE_OF
 %token TOK_VOID
@@ -50,7 +52,7 @@ void yyerror(const char* message);
 %token <character> TOK_CHAR
 
 %type <name> name char_list
-%type <node> statements statement type value condition
+%type <node> statements statement sequence sequence_items type value condition
 
 %%
 
@@ -75,6 +77,23 @@ statement
         { $$ = node_named(STMT_DECLARE, &$4, $6); }
     | TOK_COLONCOLON TOK_UNDECLARE '<' name '>' TOK_COLONCOLON TOK_COMMIT
         { $$ = node_named(STMT_UNDECLARE, &$4, NULL); }
+    | TOK_COLONCOLON TOK_ENABLE_IF '<' condition ',' sequence '>' TOK_COLONCOLON TOK_COMMIT
+        { $$ = node_block(STMT_ENABLE_IF, $4, $6); }
+    ;
+
+// the statements inside are committed one by one, without the semicolons
+sequence
+    : TOK_COLONCOLON TOK_SEQUENCE '<' sequence_items '>'
+        { $$ = $4; }
+    ;
+
+sequence_items
+    : /* nothing */
+        { $$ = NULL; }
+    | statement
+        { $$ = $1; }
+    | sequence_items ',' statement
+        { $$ = node_append($1, $3); }
     ;
 
 name