4 files changed, 101 insertions, 5 deletions

diff --git a/src/core/config.h b/src/core/config.h
index 389a146..63b131b 100644
--- a/src/core/config.h
+++ b/src/core/config.h
@@ -5,11 +5,26 @@
 // not opaque) type which the consumer of the core library is supposed to
 // assemble themselves. It contains hooks which the State will use for all effects.
 
+#include "location.h"
+
+#include <stddef.h>
+
 // This handler is used for output from the user-supplied actual program.
 typedef void (* SandPrintHandler)(const char *message, size_t length);
 
+typedef enum {
+	SAND_DIAGNOSTIC_INFO,
+	SAND_DIAGNOSTIC_WARNING,
+	SAND_DIAGNOSTIC_ERROR,
+} SandDiagnosticLevel;
+
+// This handler is used when the implementation has a report to make.
+// These could for example be displayed in tan editor's interface.
+typedef void (* SandDiagnosticHandler)(const SandLocation *, SandDiagnosticLevel, const char *message, size_t message_length);
+
 typedef struct {
 	SandPrintHandler print_handler;
+	SandDiagnosticHandler diagnostic_handler;
 } SandConfig;
 
 #endif
diff --git a/src/core/state.c b/src/core/state.c
index 91bd9e4..18448eb 100644
--- a/src/core/state.c
+++ b/src/core/state.c
@@ -1,9 +1,72 @@
 #include "state.h"
+#include "std_allocator.h"
+
+#include <assert.h>
+#include <stdarg.h>
 
 SandState sand_create_state(SandConfig config) {
-	return (SandState) {
-		.config = config,
-	};
+	SandState S;
+
+	S.config = config;
+	S.gpa = sand_get_std_allocator();
+
+	return S;
+}
+
+char *sand_vasprintf(SandAllocator *a, size_t *length_out, const char *fmt, va_list ap) {
+	va_list ap_clone;
+
+	va_copy(ap_clone, ap);
+	int length = vsnprintf(NULL, 0, fmt, ap_clone);
+	va_end(ap_clone);
+	if (length < 0) {
+		goto fail;
+	}
+
+	char *buffer = sand_allocate(a, length + 1); // Include NUL character.
+	if (buffer == NULL) {
+		goto fail;
+	}
+
+	va_copy(ap_clone, ap);
+	int final_length = vsnprintf(buffer, length + 1, fmt, ap_clone);
+	va_end(ap_clone);
+	assert(final_length == length);
+
+	if (length_out != NULL) {
+		*length_out = length;
+	}
+	return buffer;
+
+fail:
+	if (length_out != NULL) {
+		*length_out = 0;
+	}
+	return NULL;
+}
+
+_SAND_FORMAT_ATTR(printf, 3, 4)
+char *sand_asprintf(SandAllocator *a, size_t *length_out, const char *fmt, ...) {
+	va_list ap;
+	va_start(ap, fmt);
+	char *result = sand_vasprintf(a, length_out, fmt, ap);
+	va_end(ap);
+	return result;
+}
+
+void sand_print_diagnostic(SandState *S, const SandLocation *location, SandDiagnosticLevel level, const char *fmt, ...) {
+	va_list ap;
+	va_start(ap, fmt);
+	size_t message_length;
+	char *message = sand_vasprintf(&S->gpa, &message_length, fmt, ap);
+	va_end(ap);
+
+	if (message == NULL) {
+		return; // FIXME: What do we do here?
+	}
+
+	S->config.diagnostic_handler(location ,level, message, message_length);
+	sand_deallocate(&S->gpa, message, message_length + 1);
 }
 
 void sand_destroy_state(SandState *S) {
diff --git a/src/core/state.h b/src/core/state.h
index 85c604b..6f4d174 100644
--- a/src/core/state.h
+++ b/src/core/state.h
@@ -4,17 +4,22 @@
 // This module defines the evaluator state. This is the "world" in Sand.
 // Multiple evaluator states can coexist as they are totally separate.
 
+#include "utils.h"
+#include "allocator.h"
 #include "config.h"
 
-#include <stddef.h>
-
 // This data structure should be treated as entirely opaque by consuming code.
 typedef struct {
 	SandConfig config;
+
+	SandAllocator gpa;
 } SandState;
 
 SandState sand_create_state(SandConfig config);
 
+_SAND_FORMAT_ATTR(printf, 4, 5)
+void sand_print_diagnostic(SandState *, const SandLocation *, SandDiagnosticLevel, const char *fmt, ...);
+
 void sand_destroy_state(SandState *);
 
 #endif
diff --git a/src/core/utils.h b/src/core/utils.h
new file mode 100644
index 0000000..abb1665
--- /dev/null
+++ b/src/core/utils.h
@@ -0,0 +1,13 @@
+#ifndef SAND_COMPILER_ATTRIBUTES_H
+#define SAND_COMPILER_ATTRIBUTES_H
+
+// This is a helper module which defines various small helpers. It should only
+// be used internally, hence the underscore prefix.
+
+#ifdef __GNUC__
+#define _SAND_FORMAT_ATTR(archetype, string_index, first_to_check) __attribute__((format(archetype, string_index, first_to_check)))
+#else
+#define _SAND_FORMAT_ATTR(archetype, string_index, first_to_check)
+#endif
+
+#endif