xo-reader: + sequence expression (aka beginexpr or block)

src/reader/sequence_xs.cpp

@@ -0,0 +1,78 @@
+/* @file sequence_xs.cpp */
+
+#include "sequence_xs.hpp"
+#include "parserstatemachine.hpp"
+#include "expect_expr_xs.hpp"
+#include "xo/expression/Sequence.hpp"
+
+namespace xo {
+    using xo::ast::Sequence;
+
+    namespace scm {
+        std::unique_ptr<sequence_xs>
+        sequence_xs::make() {
+            return std::make_unique<sequence_xs>(sequence_xs());
+        }
+
+        void
+        sequence_xs::start(parserstatemachine * p_psm) {
+            p_psm->push_exprstate(sequence_xs::make());
+            /* want to accept anything that starts an expression,
+             * except that } ends it
+             */
+            expect_expr_xs::start(true /*allow_defs*/,
+                                  true /*cxl_on_rightbrace*/,
+                                  p_psm);
+        }
+
+        sequence_xs::sequence_xs()
+            : exprstate(exprstatetype::sequenceexpr)
+        {}
+
+        void
+        sequence_xs::on_expr(ref::brw<Expression> expr,
+                             parserstatemachine * p_psm)
+        {
+            /* TODO: if expr is a DefineExpr,
+             *       then need to rewrite...
+             *
+             *   ...prefix
+             *   DefineExpr(lhs_name, rhs)
+             *   rest...
+             *
+             * becomes:
+             *
+             *   Sequence(
+             *     ...prefix,
+             *     Apply(Lambda(gen999, [Variable(lhs_name, type(rhs))], sequencify(rest...)),
+             *           rhs))
+             *
+             * so amongst other things,
+             * helpful to have nested seequence_xs that propagates '}' instead of swallowing it.
+             */
+
+            this->expr_v_.push_back(expr.promote());
+            expect_expr_xs::start(true /*allow_defs*/,
+                                  true /*cxl_on_rightbrace*/,
+                                  p_psm);
+        }
+
+        void
+        sequence_xs::on_rightbrace_token(const token_type & /*tk*/,
+                                         parserstatemachine * p_psm)
+        {
+            auto self = p_psm->pop_exprstate();
+
+            /* make sequence from expressions seen at this level,
+             * and report it to parent
+             */
+            auto expr = Sequence::make(this->expr_v_);
+
+            p_psm->top_exprstate().on_expr(expr, p_psm);
+        }
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+
+/* end sequence_xs.cpp */