From 47e8b1bf518d89a1b6c742e2e90f57a2a2dbb1d5 Mon Sep 17 00:00:00 2001
From: CHatingPython <chatingpython@kpgpmc.org>
Date: Sun, 9 Aug 2026 17:17:47 +0200
Subject: [PATCH] feat(furc/parser): add pre- and post- conditions

---
 furc/include/furc/front/ast.hpp   | 14 ++++++++++----
 furc/include/furc/front/token.hpp |  4 ++++
 furc/src/front/lexer.cpp          |  2 ++
 furc/src/front/parser.cpp         | 22 +++++++++++++++++++++-
 furc/src/main.cpp                 |  2 +-
 5 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/furc/include/furc/front/ast.hpp b/furc/include/furc/front/ast.hpp
index 429f629..96b522b 100644
--- a/furc/include/furc/front/ast.hpp
+++ b/furc/include/furc/front/ast.hpp
@@ -116,10 +116,16 @@ struct var_decl_node final : public decl_node {
 struct func_decl_node final : public decl_node {
     decl_type_e decl_type() const override { return Function; }
 
-    std::string                   name;
-    ast_type                      type;
-    std::vector<var_decl_node>    params;
-    std::optional<comp_stmt_node> body;
+    struct def_s {
+        comp_stmt_node          body;
+        std::vector<expr_node*> preConds;
+        std::vector<expr_node*> postConds;
+    };
+
+    std::string                name;
+    ast_type                   type;
+    std::vector<var_decl_node> params;
+    std::optional<def_s>       def;
 };
 
 class expr_node : public stmt_node {
diff --git a/furc/include/furc/front/token.hpp b/furc/include/furc/front/token.hpp
index 39382db..7b7921b 100644
--- a/furc/include/furc/front/token.hpp
+++ b/furc/include/furc/front/token.hpp
@@ -76,6 +76,8 @@ struct token {
         While,   /**< `while` */
         Public,  /**< `public` */
         Private, /**< `private` */
+        Pre,     /**< `pre` */
+        Post,    /**< `post` */
 
         Pointerof, /**< `pointerof` */
         Sizeof,    /**< `sizeof` */
@@ -186,6 +188,8 @@ struct token {
         case token::While: return os << "while";
         case token::Public: return os << "public";
         case token::Private: return os << "private";
+        case token::Pre: return os << "pre";
+        case token::Post: return os << "post";
         case token::Pointerof: return os << "pointerof";
         case token::Sizeof: return os << "sizeof";
         case token::Lengthof: return os << "lengthof";
diff --git a/furc/src/front/lexer.cpp b/furc/src/front/lexer.cpp
index 0b11fbb..92c4b0c 100644
--- a/furc/src/front/lexer.cpp
+++ b/furc/src/front/lexer.cpp
@@ -52,6 +52,8 @@ token lexer::next_token() {
             { "while", token::While },
             { "public", token::Public },
             { "private", token::Private },
+            { "pre", token::Pre },
+            { "post", token::Post },
             { "pointerof", token::Pointerof },
             { "sizeof", token::Sizeof },
             { "lengthof", token::Lengthof },
diff --git a/furc/src/front/parser.cpp b/furc/src/front/parser.cpp
index 3bb27c6..6422a3d 100644
--- a/furc/src/front/parser.cpp
+++ b/furc/src/front/parser.cpp
@@ -99,7 +99,27 @@ decl_node* parser::parse_decl() {
             return m_arena->allocate<func_decl_node>(std::move(func));
         }
 
-        func.body = parse_comp();
+        func_decl_node::def_s def;
+
+        while (m_lexer.peek_token().type == token::Pre || m_lexer.peek_token().type == token::Post) {
+            auto token = m_lexer.next_token();
+            eat_token(token::LParen);
+            auto* expr = parse_expr();
+            eat_token(token::RParen);
+
+            switch (token.type) {
+            case token::Pre: {
+                def.preConds.push_back(expr);
+            } break;
+            case token::Post: {
+                def.postConds.push_back(expr);
+            } break;
+            default: throw std::runtime_error("unreachable");
+            }
+        }
+
+        def.body = parse_comp();
+        func.def = std::move(def);
 
         return m_arena->allocate<func_decl_node>(std::move(func));
     }
diff --git a/furc/src/main.cpp b/furc/src/main.cpp
index de7bc4e..8f12bf6 100644
--- a/furc/src/main.cpp
+++ b/furc/src/main.cpp
@@ -6,7 +6,7 @@ int main(void) {
     furlang::arena arena;
 
     std::string_view content = R"(
-        func main(argc: u64) -> s32 {
+        func main(argc: u64) -> s32 pre(arc > 1) {
             x: s32 = 1 + 2 * 3;
             if (x == 9) return 1;
             else return 0;