From dd52ccd9319aa847cddc486519075b806c9e9092 Mon Sep 17 00:00:00 2001
From: hachem <im@hachem.wtf>
Date: Sat, 19 Sep 2026 11:35:28 +0200
Subject: feat: emmit a decltype of a difference

---
 Makefile | 13 ++++++------
 eval.c   | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 eval.h   | 23 ++++++++++++++++++++
 main.c   |  7 +++++--
 4 files changed, 108 insertions(+), 8 deletions(-)
 create mode 100644 eval.c
 create mode 100644 eval.h

diff --git a/Makefile b/Makefile
index c107cb3..48363ba 100644
--- a/Makefile
+++ b/Makefile
@@ -1,9 +1,9 @@
-CC      = cc
+CC      = clang
 LEX     = flex
 YACC    = bison
 CFLAGS  = -std=c17 -Wall -Wextra -Werror -Wpedantic -O2 -Ibin
-SOURCES = ast.c ast.h lexer.h main.c
-OBJECTS = bin/lexer.o bin/parser.o bin/ast.o bin/main.o
+SOURCES = ast.c ast.h eval.c eval.h lexer.h main.c
+OBJECTS = bin/lexer.o bin/parser.o bin/ast.o bin/eval.o bin/main.o
 SANITIZE = -g -O0 -fsanitize=address,undefined
 
 .PHONY: all debug check format lint clean
@@ -31,8 +31,9 @@ bin/parser.o: bin/parser.c
 bin/%.o: %.c | bin
 	$(CC) $(CFLAGS) -c -o $@ $<
 
-bin/main.o: ast.h lexer.h
-bin/ast.o: ast.h lexer.h
+bin/main.o: ast.h eval.h lexer.h
+bin/ast.o:  ast.h lexer.h
+bin/eval.o: eval.h ast.h
 
 debug: CFLAGS += $(SANITIZE)
 debug: clean sfinae
@@ -47,7 +48,7 @@ format:
 	clang-format -i $(SOURCES)
 
 lint:
-	clang-tidy ast.c main.c -- -std=c17 -Ibin
+	clang-tidy ast.c eval.c main.c -- -std=c17 -Ibin
 
 clean:
 	rm -rf bin sfinae
diff --git a/eval.c b/eval.c
new file mode 100644
index 0000000..5841566
--- /dev/null
+++ b/eval.c
@@ -0,0 +1,73 @@
+#include <assert.h>
+#include <stdio.h>
+
+#include "eval.h"
+
+static int evaluate_value(const struct Node* node, long* out)
+{
+    switch (node->kind)
+    {
+        case VALUE_DIFFERENCE:
+            *out = (long)node->first->character - (long)node->second->character;
+            return 0;
+        default: break;
+    }
+
+    assert(!"the parser handed a non-value where a value goes");
+    return 1;
+}
+
+static int evaluate_type(const struct Node* node, struct Type* out)
+{
+    out->kind = KIND_VOID;
+    out->number = 0;
+    switch (node->kind)
+    {
+        case TYPE_DECLTYPE:
+            if (evaluate_value(node->first, &out->number))
+                return 1;
+            out->kind = KIND_VALUE;
+            return 0;
+        default: break;
+    }
+
+    assert(!"the parser handed a non-type where a type goes");
+    return 1;
+}
+
+static enum RunStatus emit(const struct Node* node)
+{
+    struct Type type;
+    if (evaluate_type(node->first, &type))
+        return RUN_FAILED;
+
+    if (type.kind == KIND_VALUE)
+        (void)printf("%ld\n", type.number);
+    return RUN_DONE;
+}
+
+static enum RunStatus execute_one(const struct Node* node)
+{
+    switch (node->kind)
+    {
+        case STMT_EMIT: return emit(node);
+        default: break;
+    }
+
+    assert(!"the parser handed a non-statement where a statement goes");
+    return RUN_FAILED;
+}
+
+enum RunStatus execute(const struct Node* statement)
+{
+    while (statement != NULL)
+    {
+        enum RunStatus status = execute_one(statement);
+        if (status != RUN_DONE)
+            return status;
+
+        statement = statement->next;
+    }
+
+    return RUN_DONE;
+}
diff --git a/eval.h b/eval.h
new file mode 100644
index 0000000..8b4a5f6
--- /dev/null
+++ b/eval.h
@@ -0,0 +1,23 @@
+#pragma once
+
+#include "ast.h"
+
+enum TypeKind
+{
+    KIND_VOID,
+    KIND_VALUE
+};
+
+struct Type
+{
+    enum TypeKind kind;
+    long number;
+};
+
+enum RunStatus
+{
+    RUN_DONE,
+    RUN_FAILED
+};
+
+enum RunStatus execute(const struct Node* statement);
diff --git a/main.c b/main.c
index 2d358d8..682b9db 100644
--- a/main.c
+++ b/main.c
@@ -1,16 +1,19 @@
 #include <stdio.h>
 
 #include "ast.h"
+#include "eval.h"
 #include "lexer.h"
 
 extern struct Node* program_root;
 int yyparse(void);
 
-static int parse_program(void)
+static int run_program(void)
 {
     int status = yyparse();
     if (status != 0 || lexer_failed())
         status = 1;
+    else
+        status = execute(program_root) == RUN_FAILED;
 
     node_free(program_root);
     program_root = NULL;
@@ -32,7 +35,7 @@ int main(int argc, char** argv)
         return 1;
     }
 
-    int status = parse_program();
+    int status = run_program();
     (void)fclose(yyin);
     return status;
 }
-- 
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