diff --git a/vlib/v/builder/builder.v b/vlib/v/builder/builder.v
index 9a40401486..05ca558926 100644
--- a/vlib/v/builder/builder.v
+++ b/vlib/v/builder/builder.v
@@ -9,6 +9,7 @@ import v.vmod
 import v.checker
 import v.parser
 import v.depgraph
+import v.markused
 
 pub struct Builder {
 pub:
@@ -65,6 +66,34 @@ pub fn new_builder(pref &pref.Preferences) Builder {
 	// max_nr_errors: pref.error_limit ?? 100 TODO potential syntax?
 }
 
+pub fn (mut b Builder) front_stages(v_files []string) ? {
+	util.timing_start('PARSE')
+	b.parsed_files = parser.parse_files(v_files, b.table, b.pref, b.global_scope)
+	b.parse_imports()
+	util.get_timers().show('SCAN')
+	util.get_timers().show('PARSE')
+	util.get_timers().show_if_exists('PARSE stmt')
+	if b.pref.only_check_syntax {
+		return error('stop_after_parser')
+	}
+}
+
+pub fn (mut b Builder) middle_stages() ? {
+	util.timing_start('CHECK')
+	b.table.generic_struct_insts_to_concrete()
+	b.checker.check_files(b.parsed_files)
+	util.timing_measure('CHECK')
+	b.print_warnings_and_errors()
+	if b.pref.skip_unused {
+		markused.mark_used(mut b.table, b.pref, b.parsed_files)
+	}
+}
+
+pub fn (mut b Builder) front_and_middle_stages(v_files []string) ? {
+	b.front_stages(v_files) ?
+	b.middle_stages() ?
+}
+
 // parse all deps from already parsed files
 pub fn (mut b Builder) parse_imports() {
 	mut done_imports := []string{}
diff --git a/vlib/v/builder/c.v b/vlib/v/builder/c.v
index 3f41365ebb..e39fd14c28 100644
--- a/vlib/v/builder/c.v
+++ b/vlib/v/builder/c.v
@@ -1,33 +1,12 @@
 module builder
 
 import os
-import v.parser
 import v.pref
 import v.util
 import v.gen.c
-import v.markused
 
 pub fn (mut b Builder) gen_c(v_files []string) string {
-	util.timing_start('PARSE')
-	b.parsed_files = parser.parse_files(v_files, b.table, b.pref, b.global_scope)
-	b.parse_imports()
-	util.get_timers().show('SCAN')
-	util.get_timers().show('PARSE')
-	util.get_timers().show_if_exists('PARSE stmt')
-	if b.pref.only_check_syntax {
-		return ''
-	}
-
-	util.timing_start('CHECK')
-	b.table.generic_struct_insts_to_concrete()
-	b.checker.check_files(b.parsed_files)
-	util.timing_measure('CHECK')
-
-	if b.pref.skip_unused {
-		markused.mark_used(mut b.table, b.pref, b.parsed_files)
-	}
-
-	b.print_warnings_and_errors()
+	b.front_and_middle_stages(v_files) or { return '' }
 	// TODO: move gen.cgen() to c.gen()
 	util.timing_start('C GEN')
 	res := c.gen(b.parsed_files, b.table, b.pref)
diff --git a/vlib/v/builder/js.v b/vlib/v/builder/js.v
index f92345fb6d..f136ac0ceb 100644
--- a/vlib/v/builder/js.v
+++ b/vlib/v/builder/js.v
@@ -1,29 +1,12 @@
 module builder
 
 import os
-import v.parser
 import v.pref
 import v.util
 import v.gen.js
-import v.markused
 
 pub fn (mut b Builder) gen_js(v_files []string) string {
-	util.timing_start('PARSE')
-	b.parsed_files = parser.parse_files(v_files, b.table, b.pref, b.global_scope)
-	b.parse_imports()
-	util.get_timers().show('SCAN')
-	util.get_timers().show('PARSE')
-	util.get_timers().show_if_exists('PARSE stmt')
-	//
-	util.timing_start('CHECK')
-	b.checker.check_files(b.parsed_files)
-	util.timing_measure('CHECK')
-	//
-	if b.pref.skip_unused {
-		markused.mark_used(mut b.table, b.pref, b.parsed_files)
-	}
-	b.print_warnings_and_errors()
-	//
+	b.front_and_middle_stages(v_files) or { return '' }
 	util.timing_start('JS GEN')
 	res := js.gen(b.parsed_files, b.table, b.pref)
 	util.timing_measure('JS GEN')
diff --git a/vlib/v/builder/native.v b/vlib/v/builder/native.v
index fdbdd47a00..73508a133f 100644
--- a/vlib/v/builder/native.v
+++ b/vlib/v/builder/native.v
@@ -1,29 +1,14 @@
 module builder
 
-import v.parser
 import v.pref
 import v.util
 import v.gen.native
-import v.markused
 
 pub fn (mut b Builder) build_native(v_files []string, out_file string) {
-	$if !linux && !macos {
+	if b.pref.os != .linux || b.pref.os != .macos {
 		eprintln('Warning: v -native can only generate macOS and Linux binaries for now')
 	}
-	util.timing_start('PARSE')
-	b.parsed_files = parser.parse_files(v_files, b.table, b.pref, b.global_scope)
-	b.parse_imports()
-	util.get_timers().show('SCAN')
-	util.get_timers().show('PARSE')
-	util.get_timers().show_if_exists('PARSE stmt')
-	//
-	util.timing_start('CHECK')
-	b.checker.check_files(b.parsed_files)
-	util.timing_measure('CHECK')
-	//
-	if b.pref.skip_unused {
-		markused.mark_used(mut b.table, b.pref, b.parsed_files)
-	}
+	b.front_and_middle_stages(v_files) or { return }
 	util.timing_start('Native GEN')
 	b.stats_lines, b.stats_bytes = native.gen(b.parsed_files, b.table, out_file, b.pref)
 	util.timing_measure('Native GEN')
diff --git a/vlib/v/markused/markused.v b/vlib/v/markused/markused.v
index f6c65615f6..abf8c79e04 100644
--- a/vlib/v/markused/markused.v
+++ b/vlib/v/markused/markused.v
@@ -9,12 +9,10 @@ import v.pref
 // mark_used walks the AST, starting at main() and marks all used fns transitively
 pub fn mark_used(mut table ast.Table, pref &pref.Preferences, ast_files []ast.File) {
 	mut all_fns, all_consts := all_fn_and_const(ast_files)
-
 	util.timing_start(@METHOD)
 	defer {
 		util.timing_measure(@METHOD)
 	}
-
 	mut all_fn_root_names := [
 		'main.main',
 		'__new_array',