From c4f3accbb37016b5d880903e76c351736ab6743d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=EC=A0=95=EC=8B=9C=EC=9B=90?= <sebastianrcnt@yonsei.ac.kr>
Date: Sun, 16 Aug 2026 21:16:30 +0900
Subject: [PATCH] implement M7 semantic foundation

---
 fec/src/m7.c | 114 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 114 insertions(+)
 create mode 100644 fec/src/m7.c

diff --git a/fec/src/m7.c b/fec/src/m7.c
new file mode 100644
index 0000000..a314fe3
--- /dev/null
+++ b/fec/src/m7.c
@@ -0,0 +1,114 @@
+#include "m7.h"
+#include <stdio.h>
+#include <string.h>
+
+static char *m7_generated_name(FeTypeCtx *ctx, const char *prefix)
+{
+    char number[24];
+    char *p;
+    unsigned long n;
+    sprintf(number, "%u", ctx->generated_serial++);
+    n = (unsigned long)strlen(prefix) + (unsigned long)strlen(number) + 1UL;
+    p = (char *)fe_arena_alloc(ctx->arena, n);
+    if (!p) return 0;
+    strcpy(p, prefix);
+    strcat(p, number);
+    return p;
+}
+
+int fe_m7_optional_uses_niche(const FeType *payload)
+{
+    if (!payload) return 0;
+    if (payload->kind == FE_TYPE_REF) return 1;
+    if (payload->kind == FE_TYPE_OWNED &&
+        !(payload->elem && payload->elem->kind == FE_TYPE_SLICE))
+        return 1;
+    return 0;
+}
+
+FeType *fe_m7_optional_type(FeTypeCtx *ctx, FeType *payload)
+{
+    char key[128];
+    FeType *t;
+    if (!ctx || !payload) return 0;
+    sprintf(key, "?%s", payload->name);
+    t = fe_type_intern(ctx, key);
+    if (!t) return 0;
+    if (t->kind == FE_TYPE_UNKNOWN) {
+        t->kind = FE_TYPE_OPTIONAL;
+        t->elem = payload;
+        if (!fe_m7_optional_uses_niche(payload)) {
+            t->cname = m7_generated_name(ctx, "struct fe_option_");
+            t->maker = m7_generated_name(ctx, "fe_make_option_");
+        }
+    }
+    return t;
+}
+
+int fe_m7_can_contextual_null(const FeType *expected)
+{
+    return expected && expected->kind == FE_TYPE_OPTIONAL;
+}
+
+FeType *fe_m7_error_union_type(FeTypeCtx *ctx, FeType *error_type,
+                               FeType *value_type)
+{
+    char key[160];
+    FeType *t;
+    if (!ctx || !value_type) return 0;
+    if (!error_type || strcmp(error_type->name, "core.Error") == 0)
+        return fe_type_error_union(ctx, value_type);
+    sprintf(key, "%s!%s", error_type->name, value_type->name);
+    t = fe_type_intern(ctx, key);
+    if (!t) return 0;
+    if (t->kind == FE_TYPE_UNKNOWN) {
+        t->kind = FE_TYPE_ERROR_UNION;
+        /* For FE_TYPE_ERROR_UNION, elem is the nominal error identity.
+           A null elem denotes the built-in core.Error shorthand !T. */
+        t->elem = error_type;
+        t->error_value = value_type;
+        if (value_type->kind != FE_TYPE_VOID) {
+            t->cname = m7_generated_name(ctx, "struct fe_result_");
+            t->maker = m7_generated_name(ctx, "fe_make_result_");
+            t->alloc_cname = m7_generated_name(ctx, "fe_alloc_result_");
+        }
+    }
+    return t;
+}
+
+FeType *fe_m7_error_type(FeTypeCtx *ctx, const FeType *error_union)
+{
+    if (!ctx || !error_union || error_union->kind != FE_TYPE_ERROR_UNION)
+        return 0;
+    if (error_union->elem) return error_union->elem;
+    return fe_type_intern(ctx, "core.Error");
+}
+
+FeM7ContextKind fe_m7_error_context(FeTypeCtx *ctx, const FeType *expected,
+                                    const FeType *actual)
+{
+    FeType *error_type;
+    if (!ctx || !expected || !actual ||
+        expected->kind != FE_TYPE_ERROR_UNION)
+        return FE_M7_CONTEXT_NONE;
+    if (expected->error_value && fe_type_equal(expected->error_value, actual))
+        return FE_M7_CONTEXT_SUCCESS;
+    error_type = fe_m7_error_type(ctx, expected);
+    if (error_type && fe_type_equal(error_type, actual))
+        return FE_M7_CONTEXT_FAILURE;
+    return FE_M7_CONTEXT_NONE;
+}
+
+FeM7LazyKind fe_m7_lazy_kind(const FeNode *node)
+{
+    if (!node || !node->text) return FE_M7_LAZY_NONE;
+    if (strcmp(node->text, "orelse") == 0) return FE_M7_LAZY_ORELSE;
+    if (strcmp(node->text, "catch") == 0) return FE_M7_LAZY_CATCH;
+    return FE_M7_LAZY_NONE;
+}
+
+int fe_m7_is_try(const FeNode *node)
+{
+    return node && node->kind == FE_N_UNARY && node->text &&
+           strcmp(node->text, "try") == 0;
+}