add M7 semantic foundation

fec/src/m7.h

@@ -0,0 +1,31 @@
+#ifndef FE_M7_H
+#define FE_M7_H
+
+#include "types.h"
+
+typedef enum FeM7ContextKind {
+    FE_M7_CONTEXT_NONE = 0,
+    FE_M7_CONTEXT_SUCCESS,
+    FE_M7_CONTEXT_FAILURE
+} FeM7ContextKind;
+
+typedef enum FeM7LazyKind {
+    FE_M7_LAZY_NONE = 0,
+    FE_M7_LAZY_ORELSE,
+    FE_M7_LAZY_CATCH
+} FeM7LazyKind;
+
+FeType *fe_m7_optional_type(FeTypeCtx *ctx, FeType *payload);
+int fe_m7_optional_uses_niche(const FeType *payload);
+int fe_m7_can_contextual_null(const FeType *expected);
+
+FeType *fe_m7_error_union_type(FeTypeCtx *ctx, FeType *error_type,
+                               FeType *value_type);
+FeType *fe_m7_error_type(FeTypeCtx *ctx, const FeType *error_union);
+FeM7ContextKind fe_m7_error_context(FeTypeCtx *ctx, const FeType *expected,
+                                    const FeType *actual);
+
+FeM7LazyKind fe_m7_lazy_kind(const FeNode *node);
+int fe_m7_is_try(const FeNode *node);
+
+#endif