From 8a31ee4b53c3869b649e6a8fa072731796efaf45 Mon Sep 17 00:00:00 2001
From: Simon Heuser <39399016+shsr04@users.noreply.github.com>
Date: Sun, 20 Oct 2019 09:19:37 +0200
Subject: [PATCH]  generic functions

---
 examples/hot_reload/bounce.v               |   8 +-
 vlib/compiler/comptime.v                   |  19 +-
 vlib/compiler/fn.v                         | 465 ++++++++++++++++-----
 vlib/compiler/main.v                       |  42 +-
 vlib/compiler/parser.v                     | 414 +++++++++---------
 vlib/compiler/table.v                      |  60 +--
 vlib/compiler/tests/generic_test.v         |  58 +++
 vlib/compiler/tests/print_test.v           |   3 +
 vlib/compiler/tests/repl/error.repl        |   2 +-
 vlib/compiler/tests/repl/error_nosave.repl |   2 +-
 10 files changed, 705 insertions(+), 368 deletions(-)
 create mode 100644 vlib/compiler/tests/generic_test.v
 create mode 100644 vlib/compiler/tests/print_test.v

diff --git a/examples/hot_reload/bounce.v b/examples/hot_reload/bounce.v
index 6e74cdf3ed..a2017b08e8 100644
--- a/examples/hot_reload/bounce.v
+++ b/examples/hot_reload/bounce.v
@@ -62,22 +62,22 @@ fn main() {
 }
 
 const (
-	W = 50
+	width = 50
 )
 
 [live]
 fn (game &Game) draw() {
-	game.gg.draw_rect(game.x, game.y, W, W, gx.rgb(255, 0, 0)) 
+	game.gg.draw_rect(game.x, game.y, width, width, gx.rgb(255, 0, 0)) 
 }
 
 fn (game mut Game) run() {
 	for {
 		game.x += game.dx
 		game.y += game.dy
-		if game.y >= game.height - W || game.y <= 0 {
+		if game.y >= game.height - width || game.y <= 0 {
 			game.dy = - game.dy
 		}
-		if game.x >= game.width - W || game.x <= 0 {
+		if game.x >= game.width - width || game.x <= 0 {
 			game.dx = - game.dx
 		}
 		// Refresh
diff --git a/vlib/compiler/comptime.v b/vlib/compiler/comptime.v
index c8172ce5cf..28b1062bf2 100644
--- a/vlib/compiler/comptime.v
+++ b/vlib/compiler/comptime.v
@@ -41,17 +41,17 @@ fn (p mut Parser) comp_time() {
 						stack++
 					} else if p.tok == .rcbr {
 						stack--
-					}	
+					}
 					if p.tok == .eof {
 						break
-					}	
+					}
 					if stack <= 0 && p.tok == .rcbr {
 						//p.warn('exiting $stack')
 						p.next()
 						break
-					}	
+					}
 					p.next()
-				}	
+				}
 			}	 else {
 				p.statements_no_rcbr()
 			}
@@ -185,8 +185,9 @@ fn (p mut Parser) chash() {
 			flag = flag.replace('@VROOT', p.vroot)
 			flag = flag.replace('@VMOD', v_modules_path)
 			//p.log('adding flag "$flag"')
-			_ = p.table.parse_cflag(flag, p.mod) or {
+			_p := p.table.parse_cflag(flag, p.mod) or {
 				p.error_with_token_index(err, p.cur_tok_index()-1)
+				return
 			}
 		}
 		return
@@ -219,16 +220,16 @@ fn (p mut Parser) chash() {
 		$if js {
 			for p.tok != .eof {
 				p.next()
-			}	
+			}
 		} $else {
 			p.next()
-		}	
+		}
 	}
 	else {
 		$if !js {
 			if !p.can_chash {
 				println('hash="$hash"')
-				println(hash.starts_with('include'))
+				if hash.starts_with('include') { println("include") } else {} 
 				p.error('bad token `#` (embedding C code is no longer supported)')
 			}
 		}
@@ -307,7 +308,7 @@ fn (p mut Parser) gen_struct_str(typ Type) {
 		is_public: true
 		receiver_typ: typ.name
 	})
-	
+
 	mut sb := strings.new_builder(typ.fields.len * 20)
 	sb.writeln('fn (a $typ.name) str() string {\nreturn')
 	sb.writeln("'{")
diff --git a/vlib/compiler/fn.v b/vlib/compiler/fn.v
index 64a590dcfd..e7e2d9f891 100644
--- a/vlib/compiler/fn.v
+++ b/vlib/compiler/fn.v
@@ -32,10 +32,33 @@ mut:
 	returns_error bool
 	is_decl       bool // type myfn fn(int, int)
 	defer_text    []string
-	//gen_types []string
+	is_generic		bool
+	type_pars 		[]string
+	type_inst 		[]TypeInst
+	dispatch_of		TypeInst	// current type inst of this generic instance
+	body_idx		int		// idx of the first body statement
 	fn_name_token_idx int // used by error reporting
 }
 
+struct TypeInst {
+mut:
+	// an instantiation of generic params (e.g. ["int","int","double"])
+	inst 	map[string]string
+	done	bool
+}
+
+fn (a []TypeInst) str() string {
+	mut r := []string
+	for t in a {
+		mut s := ' | '
+		for k in t.inst.keys() {
+			s += k+' -> '+ t.inst[k] +' | '
+		}
+		r << s
+	}
+	return r.str()
+}
+
 fn (p &Parser) find_var(name string) ?Var {
 	for i in 0 .. p.var_idx {
 		if p.local_vars[i].name == name {
@@ -71,21 +94,21 @@ fn (p mut Parser) open_scope() {
 fn (p mut Parser) mark_var_used(v Var) {
 	if v.idx == -1 || v.idx >= p.local_vars.len {
 		return
-	}	
+	}
 	p.local_vars[v.idx].is_used = true
 }
 
 fn (p mut Parser) mark_var_returned(v Var) {
 	if v.idx == -1 || v.idx >= p.local_vars.len {
 		return
-	}	
+	}
 	p.local_vars[v.idx].is_returned = true
 }
 
 fn (p mut Parser) mark_var_changed(v Var) {
 	if v.idx == -1 || v.idx >= p.local_vars.len {
 		return
-	}	
+	}
 	p.local_vars[v.idx].is_changed = true
 }
 
@@ -95,15 +118,22 @@ fn (p mut Parser) mark_arg_moved(v Var) {
 			//println('setting f $p.cur_fn.name arg $arg.name to is_mut')
 			p.cur_fn.args[i].is_moved = true
 			break
-		}	
-	}	
+		}
+	}
 	p.table.fns[p.cur_fn.name] = p.cur_fn
 }
 
 fn (p mut Parser) known_var(name string) bool {
 	_ = p.find_var(name) or {
 		return false
-	}	
+	}
+	return true
+}
+
+fn (p mut Parser) known_var_check_new_var(name string) bool {
+	_ = p.find_var_check_new_var(name) or {
+		return false
+	}
 	return true
 }
 
@@ -138,7 +168,7 @@ fn (p mut Parser) clear_vars() {
 fn (p mut Parser) fn_decl() {
 	p.clear_vars() // clear local vars every time a new fn is started
 	p.fgen('fn ')
-	
+
 	//defer { p.fgenln('\n') }
 	// If we are in the first pass, create a new function.
 	// In the second pass fetch the one we created.
@@ -149,12 +179,12 @@ fn (p mut Parser) fn_decl() {
 			is_public: p.tok == .key_pub
 		}
 	else {
-	}	
+	}
 	*/
 	mut f := Fn{
-		mod: p.mod
-		is_public: p.tok == .key_pub
-	}
+			mod: p.mod
+			is_public: p.tok == .key_pub
+		}
 	is_live := p.attr == 'live' && !p.pref.is_so  && p.pref.is_live
 	if p.attr == 'live' &&  p.first_pass() && !p.pref.is_live && !p.pref.is_so {
 		println('INFO: run `v -live program.v` if you want to use [live] functions')
@@ -243,7 +273,7 @@ fn (p mut Parser) fn_decl() {
 		}
 		if f.name[0] == `_` {
 			p.error('function names cannot start with `_`, use snake_case instead')
-		}	
+		}
 		if f.name.contains('__') {
 			p.error('function names cannot contain double underscores, use single underscores instead')
 		}
@@ -272,21 +302,23 @@ fn (p mut Parser) fn_decl() {
 		}
 	}
 	// Generic?
-	mut is_generic := false
 	if p.tok == .lt {
-		is_generic = true
+		f.is_generic = true
 		p.next()
-		gen_type := p.check_name()
-		if gen_type != 'T' {
-			p.error('only `T` is allowed as a generic type for now')
+		for {
+			type_par := p.check_name()
+			if type_par.len > 1 || !(type_par in reserved_type_param_names) {
+				p.error('type parameters must be single-character, upper-case letters of the following set: $reserved_type_param_names')
+			}
+			if type_par in f.type_pars {
+				p.error('redeclaration of type parameter `$type_par`')
+			}
+			f.type_pars << type_par
+			if p.tok == .gt { break }
+			p.check(.comma)
 		}
+		p.set_current_fn(f)
 		p.check(.gt)
-		if p.first_pass() {
-			p.table.register_generic_fn(f.name)
-		}  else {
-			//gen_types := p.table.fn_gen_types(f.name)
-			//println(gen_types)
-		}
 	}
 	// Args (...)
 	p.fn_args(mut f)
@@ -326,13 +358,7 @@ fn (p mut Parser) fn_decl() {
 			p.error_with_token_index('fn main must have no arguments and no return values', f.fn_name_token_idx)
 		}
 	}
-	dll_export_linkage := if p.pref.ccompiler == 'msvc' && p.attr == 'live' && p.pref.is_so {
-		'__declspec(dllexport) '
-	} else if p.attr == 'inline' {
-		'static inline '
-	} else {
-		''
-	}
+	dll_export_linkage := p.get_linkage_prefix()
 	if !p.is_vweb {
 		p.set_current_fn( f )
 	}
@@ -345,25 +371,18 @@ fn (p mut Parser) fn_decl() {
 		if p.pref.obfuscate {
 			p.genln('; // $f.name')
 		}
-		// Generate this function's body for all generic types
-		if is_generic {
-			gen_types := p.table.fn_gen_types(f.name)
-			// Remember current scanner position, go back here for each type
-			// TODO remove this once tokens are cached in `new_parser()`
-			cur_pos := p.scanner.pos
-			cur_tok := p.tok
-			cur_lit := p.lit
-			for gen_type in gen_types {
-				p.genln('$dll_export_linkage$typ ${fn_name_cgen}_$gen_type($str_args) {')
-				p.genln('// T start $p.pass ${p.strtok()}')
-				p.cur_gen_type = gen_type // TODO support more than T
-				p.statements()
-				p.scanner.pos = cur_pos
-				p.tok  = cur_tok
-				p.lit = cur_lit
+		// Generic functions are inserted as needed from the call site
+		if f.is_generic {
+			if p.first_pass() {
+				f.body_idx = p.cur_tok_index()+1
+				p.table.register_fn(f)
 			}
-		}
-		else {
+			p.check_unused_variables()
+			p.set_current_fn( EmptyFn )
+			p.returns = false
+			p.skip_fn_body()
+			return
+		} else {
 			p.gen_fn_decl(f, typ, str_args)
 		}
 	}
@@ -441,10 +460,6 @@ fn (p mut Parser) fn_decl() {
 			f.defer_text[f.scope_level] = '  ${cgen_name}_time += time__ticks() - _PROF_START;'
 		}
 	}
-	if is_generic {
-		// Don't need to generate body for the actual generic definition
-		p.cgen.nogen = true
-	}
 	p.statements_no_rcbr()
 	//p.cgen.nogen = false
 	// Print counting result after all statements in main
@@ -473,17 +488,13 @@ fn (p mut Parser) fn_decl() {
 	}
 	// Make sure all vars in this function are used (only in main for now)
 	if p.mod != 'main' {
-		if !is_generic {
-			p.genln('}')
-		}
+		p.genln('}')
 		return
 	}
+	p.genln('}')
 	p.check_unused_variables()
 	p.set_current_fn( EmptyFn )
 	p.returns = false
-	if !is_generic {
-		p.genln('}')
-	}
 }
 
 [inline]
@@ -515,6 +526,16 @@ fn (p mut Parser) skip_fn_body() {
 	}
 }
 
+fn (p Parser) get_linkage_prefix() string {
+	return if p.pref.ccompiler == 'msvc' && p.attr == 'live' && p.pref.is_so {
+		'__declspec(dllexport) '
+	} else if p.attr == 'inline' {
+		'static inline '
+	} else {
+		''
+	}
+}
+
 fn (p mut Parser) check_unused_variables() {
 	for var in p.local_vars {
 		if var.name == '' {
@@ -609,7 +630,7 @@ fn (p mut Parser) async_fn_call(f Fn, method_ph int, receiver_var, receiver_type
 }
 
 // p.tok == fn_name
-fn (p mut Parser) fn_call(f Fn, method_ph int, receiver_var, receiver_type string) {
+fn (p mut Parser) fn_call(f mut Fn, method_ph int, receiver_var, receiver_type string) {
 	if !f.is_public &&  !f.is_c && !p.pref.is_test && !f.is_interface && f.mod != p.mod  {
 		if f.name == 'contains' {
 			println('use `value in numbers` instead of `numbers.contains(value)`')
@@ -624,40 +645,48 @@ fn (p mut Parser) fn_call(f Fn, method_ph int, receiver_var, receiver_type strin
 			p.error('use `malloc()` instead of `C.malloc()`')
 		}
 	}
-	mut cgen_name := p.table.fn_gen_name(f)
-	p.next()
-	mut gen_type := ''
+	cgen_name := p.table.fn_gen_name(f)
+	p.next()		// fn name
 	if p.tok == .lt {
-		p.check(.lt)
-		gen_type = p.check_name()
-		// run<T> => run_App
-		if gen_type == 'T' && p.cur_gen_type != '' {
-			gen_type = p.cur_gen_type
+		mut i := p.token_idx
+		for {
+			if p.tokens[i].tok == .gt {
+				p.error('explicit type arguments are not allowed; remove `<...>`')
+			} else if p.tokens[i].tok == .lpar {
+				// probably a typo, do not concern the user with the above error message
+				break
+			}
+			i += 1
 		}
-		// `foo<Bar>()`
-		// If we are in the first pass, we need to add `Bar` type to the generic function `foo`,
-		// so that generic `foo`s body can be generated for each type in the second pass.
-		if p.first_pass() {
-			println('registering $gen_type in $f.name fname=$f.name')
-			p.table.register_generic_fn_type(f.name, gen_type)
-			// Function bodies are skipped in the first passed, we only need to register the generic type here.
-			return
-		}
-		cgen_name += '_' + gen_type
-		p.check(.gt)
 	}
 	// if p.pref.is_prof {
 	// p.cur_fn.called_fns << cgen_name
 	// }
-	// Normal function call
-	if !f.is_method {
-		p.gen(cgen_name)
-		p.gen('(')
-		// p.fgen(f.name)
+
+	$if windows {	// TODO fix segfault caused by `dispatch_generic_fn_instance` on Windows
+		if f.is_generic {
+			p.check(.lpar)
+			mut b := 1
+			for b > 0 {
+				if p.tok == .rpar {
+					b -= 1
+				} else if p.tok == .lpar {
+					b += 1
+				}
+				p.next()
+			}
+			p.gen('/* SKIPPED */')
+			p.warn('skipped call to generic function `$f.name`\n\tReason: generic functions are currently broken on Windows 10\n')
+			return
+		}
 	}
+
 	// If we have a method placeholder,
 	// we need to preappend "method(receiver, ...)"
-	else {
+	if f.is_method {
+		if f.is_generic {
+			p.error('generic methods are not yet implemented')
+		}
 		receiver := f.args.first()
 		//println('r=$receiver.typ RT=$receiver_type')
 		if receiver.is_mut && !p.expr_var.is_mut {
@@ -672,10 +701,23 @@ fn (p mut Parser) fn_call(f Fn, method_ph int, receiver_var, receiver_type strin
 		if !p.expr_var.is_changed {
 			p.mark_var_changed(p.expr_var)
 		}
-		p.gen_method_call(receiver_type, f.typ, cgen_name, receiver, method_ph)
+		met_name := if f.is_generic { f.name } else { cgen_name }
+		p.gen_method_call(receiver_type, f.typ, met_name, receiver, method_ph)
+	} else {
+		// Normal function call
+		p.gen('$cgen_name (')
 	}
+	
 	// foo<Bar>()
+	// if f is generic, the name is changed to a suitable instance in dispatch_generic_fn_instance()
+	// we then replace `cgen_name` with the instance's name
+	generic := f.is_generic
 	p.fn_call_args(mut f)
+	if generic {
+		p.cgen.resetln(p.cgen.cur_line.replace('$cgen_name (', '$f.name ('))
+		// println('calling inst $f.name: $p.cgen.cur_line')
+	}
+
 	p.gen(')')
 	p.calling_c = false
 	// println('end of fn call typ=$f.typ')
@@ -726,7 +768,7 @@ fn (p mut Parser) fn_args(f mut Fn) {
 		p.fspace()
 		is_mut := p.tok == .key_mut
 		if is_mut {
-			p.next()
+			p.check(.key_mut)
 		}
 		mut typ := ''
 		// variadic arg
@@ -745,7 +787,7 @@ fn (p mut Parser) fn_args(f mut Fn) {
 		} else {
 			typ = p.get_type()
 		}
-		
+
 		p.check_and_register_used_imported_type(typ)
 		if is_mut && is_primitive_type(typ) {
 			p.error('mutable arguments are only allowed for arrays, maps, and structs.' +
@@ -771,7 +813,7 @@ fn (p mut Parser) fn_args(f mut Fn) {
 			f.args << v
 		}
 		if p.tok == .comma {
-			p.next()
+			p.check(.comma)
 		}
 		// unnamed (C definition)
 		if p.tok == .ellipsis {
@@ -788,7 +830,7 @@ fn (p mut Parser) fn_args(f mut Fn) {
 }
 
 // foo *(1, 2, 3, mut bar)*
-fn (p mut Parser) fn_call_args(f mut Fn) &Fn {
+fn (p mut Parser) fn_call_args(f mut Fn) {
 	// println('fn_call_args() name=$f.name args.len=$f.args.len')
 	// C func. # of args is not known
 	p.check(.lpar)
@@ -808,14 +850,14 @@ fn (p mut Parser) fn_call_args(f mut Fn) &Fn {
 			// Cast V byteptr to C char* (byte is unsigned in V, that led to C warnings)
 			if typ == 'byte*' {
 				p.cgen.set_placeholder(ph, '(char*)')
-			}	
+			}
 			if p.tok == .comma {
 				p.gen(', ')
 				p.check(.comma)
 			}
 		}
 		p.check(.rpar)
-		return f
+		return
 	}
 	// add debug information to panic when -g arg is passed
 	if p.v.pref.is_debug && f.name == 'panic' && !p.is_js {
@@ -827,6 +869,7 @@ fn (p mut Parser) fn_call_args(f mut Fn) &Fn {
 			'panic_debug ($p.scanner.line_nr, tos3("$file_path"), tos3("$mod_name"), tos2((byte *)"$fn_name"), '
 		))
 	}
+	mut saved_args := []string
 	for i, arg in f.args {
 		// Receiver is the first arg
 		// Skip the receiver, because it was already generated in the expression
@@ -857,7 +900,7 @@ fn (p mut Parser) fn_call_args(f mut Fn) &Fn {
 				if i < f.args.len - 1 {
 					dots_example = dots_example + ',..'
 				}
-				p.error('`$arg.name` is a mutable argument, you need to provide `mut`: `$f.name($dots_example)`')	
+				p.error('`$arg.name` is a mutable argument, you need to provide `mut`: `$f.name($dots_example)`')
 			}
 			if p.peek() != .name {
 				p.error('`$arg.name` is a mutable argument, you need to provide a variable to modify: `$f.name(... mut a...)`')
@@ -876,7 +919,7 @@ fn (p mut Parser) fn_call_args(f mut Fn) &Fn {
 		clone := p.pref.autofree && arg.typ == 'string' && arg.is_moved && p.mod != 'builtin'
 		if clone {
 			p.gen('/*YY f=$f.name arg=$arg.name is_moved=$arg.is_moved*/string_clone(')
-		}	
+		}
 		mut typ := p.bool_expression()
 		if typ.starts_with('...') { typ = typ.right(3) }
 		if clone {
@@ -923,7 +966,7 @@ fn (p mut Parser) fn_call_args(f mut Fn) &Fn {
 					p.cgen.set_placeholder(ph, '${typ}_str(')
 					p.gen(')')
 					continue
-				}	
+				}
 				error_msg := ('`$typ` needs to have method `str() string` to be printable')
 				p.error(error_msg)
 			}
@@ -937,11 +980,15 @@ fn (p mut Parser) fn_call_args(f mut Fn) &Fn {
 		got_ptr := got.ends_with('*')
 		exp_ptr := expected.ends_with('*')
 		// println('fn arg got="$got" exp="$expected"')
-		if !p.check_types_no_throw(got, expected) {
+		type_mismatch := !p.check_types_no_throw(got, expected)
+		if type_mismatch && f.is_generic {
+			// println("argument `$arg.name` is generic")
+			saved_args << got
+		} else if type_mismatch {
 			mut j := i
 			if f.is_method {
 				j--
-			}	
+			}
 			mut nr := '${i+1}th'
 			if j == 0 {
 				nr = 'first'
@@ -949,9 +996,11 @@ fn (p mut Parser) fn_call_args(f mut Fn) &Fn {
 				nr = 'second'
 			}	 else if j == 2 {
 				nr = 'third'
-			}	
+			}
 			p.error('cannot use type `$typ` as type `$arg.typ` in $nr ' +
 				'argument to `$f.name()`')
+		} else {
+			saved_args << ''
 		}
 		is_interface := p.table.is_interface(arg.typ)
 		// Automatically add `&` or `*` before an argument.
@@ -1019,7 +1068,105 @@ fn (p mut Parser) fn_call_args(f mut Fn) &Fn {
 		p.error('wrong number of arguments for fn `$f.name`: expected $f.args.len, but got more')
 	}
 	p.check(.rpar)
-	return f // TODO is return f right?
+	if f.is_generic {
+		type_map := p.extract_type_inst(f, saved_args)
+		p.dispatch_generic_fn_instance(mut f, type_map)
+	}
+}
+
+// From a given generic function and an argument list matching its signature,
+// create a type instantiation
+fn (p mut Parser) extract_type_inst(f &Fn, args_ []string) TypeInst {
+	mut r := TypeInst{}
+	mut i := 0
+	mut args := args_
+	args << f.typ
+	for ai, e in args {
+		if e == '' { continue }
+		tp := f.type_pars[i]
+		mut ti := e
+		if ti.starts_with('fn (') {
+			fn_args := ti.right(4).all_before(') ').split(',')
+			mut found := false
+			for fa_ in fn_args {
+				mut fa := fa_
+				for fa.starts_with('array_') { fa = fa.right(6) }
+				if fa == tp {
+					r.inst[tp] = fa
+					found = true
+					i += 1
+					break
+				}
+			}
+			if found { continue }
+			ti = ti.all_after(') ')
+		}
+		for ti.starts_with('array_') { ti = ti.right(6) }
+		if r.inst[tp] != '' {
+			if r.inst[tp] != ti {
+				p.error('type parameter `$tp` has type ${r.inst[tp]}, not `$ti`')
+			}
+			continue
+		}
+		// println("extracted $tp => $ti")
+		r.inst[tp] = ti
+		i += 1
+		if i >= f.type_pars.len { break }
+	}
+	if r.inst[f.typ] == '' && f.typ in f.type_pars {
+		r.inst[f.typ] = '_ANYTYPE_'
+	}
+	return r
+}
+
+// Replace type params of a given generic function using a TypeInst
+fn (p mut Parser) replace_type_params(f &Fn, ti TypeInst) []string {
+	mut sig := []string
+	for a in f.args {
+		sig << a.typ
+	}
+	sig << f.typ
+	mut r := []string
+	for _, a in sig {
+		mut fi := a
+		mut fr := ''
+		if fi.starts_with('fn (') {
+			fr += 'fn ('
+			mut fn_args := fi.right(4).all_before(') ').split(',')
+			fn_args << fi.all_after(') ')
+			for i, fa_ in fn_args {
+				mut fna := fa_.trim_space()
+				for fna.starts_with('array_') {
+					fna = fna.right(6)
+					fr += 'array_'
+				}
+				if fna in ti.inst.keys() {
+					fr += ti.inst[fna]
+				} else {
+					fr += fna
+				}
+				if i <= fn_args.len-3 {
+					fr += ','
+				} else if i == fn_args.len-2 {
+					fr += ') '
+				}
+			}
+			r << fr
+			continue
+		}
+		for fi.starts_with('array_') { 
+			fi = fi.right(6)
+			fr += 'array_'
+		}
+		if fi in ti.inst.keys() {
+			fr += ti.inst[fi]
+			// println("replaced $a => $fr")
+		} else {
+			fr += fi
+		}
+		r << fr
+	}
+	return r
 }
 
 fn (p mut Parser) fn_register_vargs_stuct(f &Fn, typ string, values []string) string {
@@ -1067,7 +1214,7 @@ fn (p mut Parser) fn_gen_caller_vargs(f mut Fn) {
 	}
 	vargs_struct := p.fn_register_vargs_stuct(f, varg_def_type, values)
 	p.cgen.gen('&($vargs_struct){.len=$values.len,.args={'+values.join(',')+'}}')
-	
+
 }
 
 fn (p mut Parser) register_multi_return_stuct(types []string) string {
@@ -1085,6 +1232,118 @@ fn (p mut Parser) register_multi_return_stuct(types []string) string {
 	return typ
 }
 
+fn (p mut Parser) dispatch_generic_fn_instance(f mut Fn, ti TypeInst) {
+	$if windows {
+		p.error('feature disabled on Windows')
+	}
+	mut new_inst := true
+	for e in f.type_inst {
+		if e.inst.str() == ti.inst.str() {
+			new_inst = false
+			break
+		}
+	}
+
+	if !new_inst {
+		f.name = f.name + '_T'
+		for k in ti.inst.keys() {
+			f.name = f.name + '_' + type_to_safe_str(ti.inst[k])
+		}
+		_f := p.table.find_fn(f.name) or {
+			p.error('function instance `$f.name` not found')
+			return
+		}
+		f.args = _f.args
+		f.typ = _f.typ
+		f.is_generic = false
+		f.type_inst = []TypeInst
+		f.dispatch_of = ti
+		// println('using existing inst $f.name(${f.str_args(p.table)}) $f.typ')
+		return
+	}
+
+	f.type_inst << ti
+	p.table.register_fn(f)
+	// Remember current scanner position, go back here for each type instance
+	// TODO remove this once tokens are cached in `new_parser()`
+	saved_tok_idx := p.cur_tok_index()
+	saved_fn := p.cur_fn
+	saved_var_idx := p.var_idx
+	saved_local_vars := p.local_vars
+	p.clear_vars()
+	saved_line := p.cgen.cur_line
+	saved_lines := p.cgen.lines
+	saved_is_tmp := p.cgen.is_tmp
+	saved_tmp_line := p.cgen.tmp_line
+	returns := p.returns		// should be always false
+
+	f.name = f.name + '_T'
+	for k in ti.inst.keys() {
+		f.name = f.name + '_' + type_to_safe_str(ti.inst[k])
+	}
+	f.is_generic = false		// the instance is a normal function
+	f.type_inst = []TypeInst
+	f.scope_level = 0
+	f.dispatch_of = ti
+	old_args := f.args
+	new_types := p.replace_type_params(f, ti)
+	f.args = []Var
+	for i in 0..new_types.len-1 {
+		mut v := old_args[i]
+		v.typ = new_types[i]
+		f.args << v
+	}
+	f.typ = new_types.last()
+	if f.typ in f.type_pars { f.typ = '_ANYTYPE_' }
+
+	if f.typ in ti.inst {
+		f.typ = ti.inst[f.typ]
+	}
+	p.table.register_fn(f)
+	// println("generating gen inst $f.name(${f.str_args(p.table)}) $f.typ : $ti.inst")
+
+	p.cgen.is_tmp = false
+	p.returns = false
+	p.cgen.tmp_line = ''
+	p.cgen.cur_line = ''
+	p.cgen.lines = []string
+	p.cur_fn = *f
+	for arg in f.args {
+		p.register_var(arg)
+	}
+	p.token_idx = f.body_idx-1
+	p.next()	// re-initializes the parser properly
+	str_args := f.str_args(p.table)
+
+	p.in_dispatch = true
+	p.genln('${p.get_linkage_prefix()}$f.typ $f.name($str_args) {')
+	// p.genln('/* generic fn instance $f.name : $ti.inst */')
+	p.statements()
+	p.in_dispatch = false
+
+	if f.typ == '_ANYTYPE_' {
+		f.typ = p.cur_fn.typ
+		f.name = f.name.replace('_ANYTYPE_', type_to_safe_str(f.typ))
+		p.cgen.lines[0] = p.cgen.lines[0].replace('_ANYTYPE_', f.typ)
+		p.table.register_fn(f)
+	}
+	for l in p.cgen.lines {
+		p.cgen.fns << l
+	}
+
+	p.token_idx = saved_tok_idx-1
+	p.next()
+	p.check(.rpar)		// end of the arg list which caused this dispatch
+	p.cur_fn = saved_fn
+	p.var_idx = saved_var_idx
+	p.local_vars = saved_local_vars
+	p.cgen.lines = saved_lines
+	p.cgen.cur_line = saved_line
+	p.cgen.is_tmp = saved_is_tmp
+	p.cgen.tmp_line = saved_tmp_line
+	p.returns = false
+}
+
 // "fn (int, string) int"
 fn (f &Fn) typ_str() string {
 	mut sb := strings.new_builder(50)
@@ -1162,7 +1421,7 @@ fn (fns []Fn) contains(f Fn) bool {
 	for ff in fns {
 		if ff.name == f.name {
 			return true
-		}	
-	}	
+		}
+	}
 	return false
-}	
+}
diff --git a/vlib/compiler/main.v b/vlib/compiler/main.v
index 82520562cf..616f88186d 100644
--- a/vlib/compiler/main.v
+++ b/vlib/compiler/main.v
@@ -89,14 +89,14 @@ pub mut:
 	is_run        bool
 	show_c_cmd    bool   // `v -show_c_cmd` prints the C command to build program.v.c
 	sanitize      bool   // use Clang's new "-fsanitize" option
-	
+
 	is_debug      bool   // false by default, turned on by -g or -cg, it tells v to pass -g to the C backend compiler.
 	is_vlines     bool   // turned on by -g, false by default (it slows down .tmp.c generation slightly).
 	is_keep_c     bool   // -keep_c , tell v to leave the generated .tmp.c alone (since by default v will delete them after c backend finishes)
 	// NB: passing -cg instead of -g will set is_vlines to false and is_g to true, thus making v generate cleaner C files,
 	// which are sometimes easier to debug / inspect manually than the .tmp.c files by plain -g (when/if v line number generation breaks).
 	is_cache      bool   // turns on v usage of the module cache to speed up compilation.
-	
+
 	is_stats      bool   // `v -stats file_test.v` will produce more detailed statistics for the tests that were run
 	no_auto_free  bool   // `v -nofree` disable automatic `free()` insertion for better performance in some applications  (e.g. compilers)
 	cflags        string // Additional options which will be passed to the C compiler.
@@ -114,7 +114,7 @@ pub mut:
 }
 
 // Should be called by main at the end of the compilation process, to cleanup
-pub fn (v mut V) finalize_compilation(){	
+pub fn (v mut V) finalize_compilation(){
 	// TODO remove
 	if v.pref.autofree {
 		println('started freeing v struct')
@@ -126,12 +126,12 @@ pub fn (v mut V) finalize_compilation(){
 			//f.local_vars.free()
 			f.args.free()
 			//f.defer_text.free()
-		}	
+		}
 		v.table.fns.free()
 		free(v.table)
-		//for p in parsers {}	
+		//for p in parsers {}
 		println('done!')
-	}	
+	}
 }
 
 pub fn (v mut V) add_parser(parser Parser) {
@@ -142,7 +142,7 @@ pub fn (v &V) get_file_parser_index(file string) ?int {
 	for i, p in v.parsers {
 		if os.realpath(p.file_path_id) == os.realpath(file) {
 			return i
-		}	
+		}
 	}
 	return error('parser for "$file" not found')
 }
@@ -184,11 +184,11 @@ pub fn (v mut V) compile() {
 		println('\nparsers:')
 		for q in v.parsers {
 			println(q.file_name)
-		}	
+		}
 		println('\nfiles:')
 		for q in v.files {
 			println(q)
-		}	
+		}
 	}
 	*/
 	// First pass (declarations)
@@ -251,7 +251,7 @@ pub fn (v mut V) compile() {
 	mut defs_pos := cgen.lines.len - 1
 	if defs_pos == -1 {
 		defs_pos = 0
-	}	
+	}
 	cgen.nogen = q
 	for file in v.files {
 		v.parse(file, .main)
@@ -272,7 +272,7 @@ pub fn (v mut V) compile() {
 	v.vgen_buf.free()
 	vgen_parser.parse(.main)
 	// v.parsers.add(vgen_parser)
-	
+
 	// All definitions
 	mut def := strings.new_builder(10000)// Avoid unnecessary allocations
 	$if !js {
@@ -303,7 +303,7 @@ pub fn (v mut V) compile() {
 	}
 	$if js {
 		cgen.genln('main__main();')
-	}	
+	}
 	cgen.save()
 	v.cc()
 }
@@ -420,13 +420,13 @@ pub fn (v mut V) generate_main() {
 			}
 			// Generate a C `main`, which calls every single test function
 			v.gen_main_start(false)
-			
+
 			if v.pref.is_stats { cgen.genln('BenchedTests bt = main__start_testing();') }
-			
+
 			for _, f in v.table.fns {
 				if f.name.starts_with('main__test_') {
 					if v.pref.is_stats { cgen.genln('BenchedTests_testing_step_start(&bt, tos3("$f.name"));') }
-					cgen.genln('$f.name();')					
+					cgen.genln('$f.name();')
 					if v.pref.is_stats { cgen.genln('BenchedTests_testing_step_end(&bt);') }
 				}
 			}
@@ -471,7 +471,7 @@ pub fn final_target_out_name(out_name string) string {
 pub fn (v V) run_compiled_executable_and_exit() {
 	if v.pref.is_verbose {
 		println('============ running $v.out_name ============')
-	}	
+	}
 	mut cmd := '"' + final_target_out_name(v.out_name).replace('.exe','') + '"'
 	if os.args.len > 3 {
 		cmd += ' ' + os.args.right(3).join(' ')
@@ -631,7 +631,7 @@ pub fn (v &V)  get_user_files() []string {
 		user_files << os.join(v.vroot, 'vlib', 'benchmark', 'tests',
 			'always_imported.v')
 	}
-	
+
 	// v volt/slack_test.v: compile all .v files to get the environment
 	// I need to implement user packages! TODO
 	is_test_with_imports := dir.ends_with('_test.v') &&
@@ -754,14 +754,14 @@ pub fn new_v(args[]string) &V {
 		os.mkdir(v_modules_path)
 		os.mkdir('$v_modules_path${os.path_separator}cache')
 	}
-	
+
 	mut vgen_buf := strings.new_builder(1000)
 	vgen_buf.writeln('module main\nimport strings')
-	
+
 	joined_args := args.join(' ')
 	target_os := get_arg(joined_args, 'os', '')
 	mut out_name := get_arg(joined_args, 'o', 'a.out')
-	
+
 	mut dir := args.last()
 	if 'run' in args {
 		dir = get_param_after(joined_args, 'run', '')
@@ -891,7 +891,7 @@ pub fn new_v(args[]string) &V {
 		is_vlines:     '-g' in args && !('-cg' in args)
 		is_keep_c:     '-keep_c' in args
 		is_cache:      '-cache' in args
-				
+
 		is_stats: '-stats' in args
 		obfuscate: obfuscate
 		is_prof: '-prof' in args
diff --git a/vlib/compiler/parser.v b/vlib/compiler/parser.v
index 47b7a22555..fb97e43eab 100644
--- a/vlib/compiler/parser.v
+++ b/vlib/compiler/parser.v
@@ -59,9 +59,9 @@ mut:
 	calling_c      bool
 	cur_fn         Fn
 	local_vars     []Var // local function variables
-	var_idx       int
-	returns        bool
-	vroot          string
+	var_idx       	int
+	returns        	bool
+	vroot          	string
 	is_c_struct_init bool
 	is_empty_c_struct_init bool
 	is_c_fn_call bool
@@ -71,7 +71,7 @@ mut:
 	var_decl_name string 	// To allow declaring the variable so that it can be used in the struct initialization
 	is_alloc   bool // Whether current expression resulted in an allocation
 	is_const_literal bool // `1`, `2.0` etc, so that `u64_var == 0` works
-	cur_gen_type string // "App" to replace "T" in current generic function
+	in_dispatch 	bool		// dispatching generic instance?
 	is_vweb bool
 	is_sql bool
 	is_js bool
@@ -671,7 +671,11 @@ fn (p mut Parser) struct_decl() {
 	}
 	mut typ := p.table.find_type(name)
 	if p.pass == .decl && p.table.known_type_fast(typ) {
-		p.error('`$name` redeclared')
+		if name in reserved_type_param_names {
+			p.error('name `$name` is reserved for type parameters')
+		} else {
+			p.error('type `$name` redeclared')
+		}
 	}
 	if is_objc {
 		// Forward declaration of an Objective-C interface with `@class` :)
@@ -1030,7 +1034,8 @@ fn (p mut Parser) get_type() string {
 		p.register_map(typ)
 		return typ
 	}
-	//
+	
+	// ptr/ref
 	mut warn := false
 	for p.tok == .mul {
 		if p.first_pass() {
@@ -1045,7 +1050,16 @@ fn (p mut Parser) get_type() string {
 		nr_muls++
 		p.check(.amp)
 	}
-	typ += p.lit
+
+	// Generic type check
+	ti := p.cur_fn.dispatch_of.inst
+	if p.lit in ti.keys() {
+		typ += ti[p.lit]
+		// println('cur dispatch: $p.lit => $typ')
+	} else {
+		typ += p.lit
+	}
+
 	if !p.is_struct_init {
 		// Otherwise we get `foo := FooFoo{` because `Foo` was already
 		// generated in name_expr()
@@ -1164,8 +1178,7 @@ fn (p mut Parser) statements_no_rcbr() string {
 	mut last_st_typ := ''
 	for p.tok != .rcbr && p.tok != .eof && p.tok != .key_case &&
 		p.tok != .key_default && p.peek() != .arrow {
-		// println(p.tok.str())
-		// p.print_tok()
+		// println('stm: '+p.tok.str()+', next: '+p.peek().str())
 		last_st_typ = p.statement(true)
 		// println('last st typ=$last_st_typ')
 		if !p.inside_if_expr {
@@ -1186,7 +1199,6 @@ fn (p mut Parser) statements_no_rcbr() string {
 		// p.check(.rcbr)
 	}
 	//p.fmt_dec()
-	// println('close scope line=$p.scanner.line_nr')
 
 	p.close_scope()
 	return last_st_typ
@@ -1255,7 +1267,9 @@ fn (p mut Parser) statement(add_semi bool) string {
 	if p.returns && !p.is_vweb {
 		p.error('unreachable code')
 	}
-	p.cgen.is_tmp = false
+	// if !p.in_dispatch {
+		p.cgen.is_tmp = false
+	// }
 	tok := p.tok
 	mut q := ''
 	switch tok {
@@ -1719,73 +1733,43 @@ fn (p mut Parser) name_expr() string {
 	// known_type := p.table.known_type(name)
 	orig_name := name
 	is_c := name == 'C' && p.peek() == .dot
-	mut is_c_struct_init := is_c && ptr// a := &C.mycstruct{}
+
 	if is_c {
-		p.next()
+		p.check(.name)
 		p.check(.dot)
 		name = p.lit
-		p.fgen(name)
-		// Currently struct init is set to true only we have `&C.Foo{}`, handle `C.Foo{}`:
-		if !is_c_struct_init && p.peek() == .lcbr {
-			is_c_struct_init = true
+		// C struct initialization
+		if p.peek() == .lcbr && p.table.known_type(name) {
+			return p.get_struct_type(name, true, ptr)
 		}
+		// C function
+		if p.peek() == .lpar {
+			return p.get_c_func_type(name)
+		}
+		// C const (`C.GLFW_KEY_LEFT`)
+		p.gen(name)
+		p.next()
+		return 'int'
 	}
+
 	// enum value? (`color == .green`)
 	if p.tok == .dot {
-		//println('got enum dot val $p.left_type pass=$p.pass $p.scanner.line_nr left=$p.left_type')
-		T := p.find_type(p.expected_type)
-		if T.cat == .enum_ {
-			p.check(.dot)
-			val := p.check_name()
-			// Make sure this enum value exists
-			if !T.has_enum_val(val) {
-				p.error('enum `$T.name` does not have value `$val`')
-			}
-			p.gen(mod_gen_name(T.mod) + '__' + p.expected_type + '_' + val)
+		if p.table.known_type(p.expected_type) {
+			p.check_enum_member_access()
+			// println("found enum value: $p.expected_type")
+			return p.expected_type
+		} else {
+			p.error("unknown enum: `$p.expected_type`")
 		}
-		return p.expected_type
 	}
+
 	// Variable, checked before modules, so module shadowing is allowed.
 	// (`gg = gg.newcontext(); gg.draw_rect(...)`)
-	for { // TODO remove
-	mut v := p.find_var_check_new_var(name) or { break }
-	if name == '_' {
-		p.error('cannot use `_` as value')
+	if p.known_var_check_new_var(name) {
+		rtyp := p.get_var_type(name, ptr, deref)
+		return rtyp
 	}
-	if ptr {
-		p.gen('&')
-	}
-	else if deref {
-		p.gen('*')
-	}
-	if p.pref.autofree && v.typ == 'string' && v.is_arg &&
-		p.assigned_type == 'string' {
-		p.warn('setting moved ' + v.typ)
-		p.mark_arg_moved(v)
-	}
-	mut typ := p.var_expr(v)
-	// *var
-	if deref {
-		if !typ.contains('*') && !typ.ends_with('ptr') {
-			println('name="$name", t=$v.typ')
-			p.error('dereferencing requires a pointer, but got `$typ`')
-		}
-		typ = typ.replace('ptr', '')// TODO
-		typ = typ.replace('*', '')// TODO
-	}
-	// &var
-	else if ptr {
-		typ += '*'
-	}
-	if p.inside_return_expr {
-		//println('marking $v.name returned')
-		p.mark_var_returned(v)
-		// v.is_returned = true // TODO modifying a local variable
-		// that's not used afterwards, this should be a compilation
-		// error
-	}
-	return typ
-	} // TODO REMOVE for{}
+
 	// Module?
 	if p.peek() == .dot && ((name == p.mod && p.table.known_mod(name)) ||
 		p.import_table.known_alias(name))	&& !is_c {
@@ -1801,6 +1785,7 @@ fn (p mut Parser) name_expr() string {
 		p.fgen(name)
 		name = prepend_mod(mod_gen_name(mod), name)
 	}
+
 	// Unknown name, try prepending the module name to it
 	// TODO perf
 	else if !p.table.known_type(name) &&
@@ -1809,52 +1794,15 @@ fn (p mut Parser) name_expr() string {
 		name = p.prepend_mod(name)
 	}
 
-	// Variable, checked before modules, so module shadowing is allowed.
-	// (`gg = gg.newcontext(); gg.draw_rect(...)`)
-	for { // TODO remove
-	mut v := p.find_var_check_new_var(name) or { break }
-	if name == '_' {
-		p.error('cannot use `_` as value')
+	// re-check
+	if p.known_var_check_new_var(name) {
+		return p.get_var_type(name, ptr, deref)
 	}
-	if ptr {
-		p.gen('&')
-	}
-	else if deref {
-		p.gen('*')
-	}
-	if p.pref.autofree && v.typ == 'string' && v.is_arg &&
-		p.assigned_type == 'string' {
-		p.warn('setting moved ' + v.typ)
-		p.mark_arg_moved(v)
-	}
-	mut typ := p.var_expr(v)
-	// *var
-	if deref {
-		if !typ.contains('*') && !typ.ends_with('ptr') {
-			println('name="$name", t=$v.typ')
-			p.error('dereferencing requires a pointer, but got `$typ`')
-		}
-		typ = typ.replace('ptr', '')// TODO
-		typ = typ.replace('*', '')// TODO
-	}
-	// &var
-	else if ptr {
-		typ += '*'
-	}
-	if p.inside_return_expr {
-		//println('marking $v.name returned')
-		p.mark_var_returned(v)
-		// v.is_returned = true // TODO modifying a local variable
-		// that's not used afterwards, this should be a compilation
-		// error
-	}
-	return typ
-	} // TODO REMOVE for{}
 
 	// if known_type || is_c_struct_init || (p.first_pass() && p.peek() == .lcbr) {
 	// known type? int(4.5) or Color.green (enum)
 	if p.table.known_type(name) {
-		// float(5), byte(0), (*int)(ptr) etc
+		// cast expression: float(5), byte(0), (*int)(ptr) etc
 		if !is_c && ( p.peek() == .lpar || (deref && p.peek() == .rpar) ) {
 			if deref {
 				name += '*'
@@ -1885,87 +1833,20 @@ fn (p mut Parser) name_expr() string {
 			p.next()
 			return enum_type.name
 		}
-		// struct initialization
+		// normal struct init (non-C)
 		else if p.peek() == .lcbr {
-			if ptr {
-					name += '*'  // `&User{}` => type `User*`
-			}
-			if name == 'T' {
-				name = p.cur_gen_type
-			}
-			p.is_c_struct_init = is_c_struct_init
-			return p.struct_init(name)
+			return p.get_struct_type(name, false, ptr)
 		}
 	}
-	if is_c {
-		// C const (`C.GLFW_KEY_LEFT`)
-		if p.peek() != .lpar {
-			p.gen(name)
-			p.next()
-			return 'int'
-		}
-		// C function
-		f := Fn {
-			name: name
-			is_c: true
-		}
-		p.is_c_fn_call = true
-		p.fn_call(f, 0, '', '')
-		p.is_c_fn_call = false
-		// Try looking it up. Maybe its defined with "C.fn_name() fn_type",
-		// then we know what type it returns
-		cfn := p.table.find_fn(name) or {
-			// Not Found? Return 'void*'
-			//return 'cvoid' //'void*'
-			if false {
-			p.warn('\ndefine imported C function with ' +
-				'`fn C.$name([args]) [return_type]`\n')
-			}
-			return 'void*'
-		}
-		return cfn.typ
-	}
+
 	// Constant
-	for {
-		c := p.table.find_const(name) or { break }
-		if ptr && !c.is_global {
-			p.error('cannot take the address of constant `$c.name`')
-		} else if ptr && c.is_global {
-			// c.ptr = true
-			p.gen('& /*const*/ ')
-		}
-		mut typ := p.var_expr(c)
-		if ptr {
-			typ += '*'
-		}
-		return typ
+	if p.table.known_const(name) {
+		return p.get_const_type(name, ptr)
 	}
-	// Function (not method btw, methods are handled in `dot()`)
+
+	// Function (not method btw, methods are handled in dot())	
 	mut f := p.table.find_fn_is_script(name, p.v_script) or {
-		// We are in the second pass, that means this function was not defined,
-		// throw an error.
-		if !p.first_pass() {
-			// check for misspelled function / variable / module
-			suggested := p.identify_typo(name, p.import_table)
-			if suggested != '' {
-				p.error('undefined: `$name`. did you mean:$suggested')
-			}
-			// If orig_name is a mod, then printing undefined: `mod` tells us nothing
-			if p.table.known_mod(orig_name) || p.import_table.known_alias(orig_name) {
-				name = name.replace('__', '.')
-				p.error('undefined: `$name`')
-			}
-			else {
-				p.error('undefined: `$orig_name`')
-			}
-		} else {
-			p.next()
-			// First pass, the function can be defined later.
-			// Only in const definitions? (since fn bodies are skipped
-			// in the first pass).
-			return 'void'
-		}
-		return 'void'
+		return p.get_undefined_fn_type(name, orig_name)
 	}
 	// no () after func, so func is an argument, just gen its name
 	// TODO verify this and handle errors
@@ -1986,8 +1867,20 @@ fn (p mut Parser) name_expr() string {
 	if f.typ == 'void' && !p.inside_if_expr {
 		// p.error('`$f.name` used as value')
 	}
-	//p.log('calling function')
-	p.fn_call(f, 0, '', '')
+
+	// println('call to fn $f.name of type $f.typ')
+	// TODO replace the following dirty hacks (needs ptr access to fn table)
+	new_f := f
+	p.fn_call(mut new_f, 0, '', '')
+	if f.is_generic {
+		f2 := p.table.find_fn(f.name) or {
+			return ''
+		}
+		// println('after call of generic instance $new_f.name(${new_f.str_args(p.table)}) $new_f.typ')
+		// println('	from $f2.name(${f2.str_args(p.table)}) $f2.typ : $f2.type_inst')
+	}
+	f = new_f
+
 	// dot after a function call: `get_user().age`
 	if p.tok == .dot {
 		mut typ := ''
@@ -2005,6 +1898,146 @@ fn (p mut Parser) name_expr() string {
 	return f.typ
 }
 
+fn (p mut Parser) get_struct_type(name_ string, is_c bool, is_ptr bool) string {
+	mut name := name_
+	if is_ptr {
+		name += '*'  // `&User{}` => type `User*`
+	}
+	if name in reserved_type_param_names {
+		p.warn('name `$name` is reserved for type parameters')
+	}
+	p.is_c_struct_init = is_c
+	return p.struct_init(name)
+}
+
+fn (p mut Parser) check_enum_member_access() {
+	T := p.find_type(p.expected_type)
+	if T.cat == .enum_ {
+		p.check(.dot)
+		val := p.check_name()
+		// Make sure this enum value exists
+		if !T.has_enum_val(val) {
+			p.error('enum `$T.name` does not have value `$val`')
+		}
+		p.gen(mod_gen_name(T.mod) + '__' + p.expected_type + '_' + val)
+	} else {
+		p.error('`$T.name` is not an enum')
+	}
+}
+
+fn (p mut Parser) get_var_type(name string, is_ptr bool, is_deref bool) string {
+	v := p.find_var_check_new_var(name) or { return "" }
+	if name == '_' {
+		p.error('cannot use `_` as value')
+	}
+	if is_ptr {
+		p.gen('&')
+	}
+	else if is_deref {
+		p.gen('*')
+	}
+	if p.pref.autofree && v.typ == 'string' && v.is_arg &&
+		p.assigned_type == 'string' {
+		p.warn('setting moved ' + v.typ)
+		p.mark_arg_moved(v)
+	}
+	mut typ := p.var_expr(v)
+	// *var
+	if is_deref {
+		if !typ.contains('*') && !typ.ends_with('ptr') {
+			println('name="$name", t=$v.typ')
+			p.error('dereferencing requires a pointer, but got `$typ`')
+		}
+		typ = typ.replace('ptr', '')// TODO
+		typ = typ.replace('*', '')// TODO
+	}
+	// &var
+	else if is_ptr {
+		typ += '*'
+	}
+	if p.inside_return_expr {
+		//println('marking $v.name returned')
+		p.mark_var_returned(v)
+		// v.is_returned = true // TODO modifying a local variable
+		// that's not used afterwards, this should be a compilation
+		// error
+	}
+	return typ
+}
+
+fn (p mut Parser) get_const_type(name string, is_ptr bool) string {
+	c := p.table.find_const(name) or { return "" }
+	if is_ptr && !c.is_global {
+		p.error('cannot take the address of constant `$c.name`')
+	} else if is_ptr && c.is_global {
+		// c.ptr = true
+		p.gen('& /*const*/ ')
+	}
+	mut typ := p.var_expr(c)
+	if is_ptr {
+		typ += '*'
+	}
+	return typ
+}
+
+fn (p mut Parser) get_c_func_type(name string) string {
+	f := Fn {
+		name: name
+		is_c: true
+	}
+	p.is_c_fn_call = true
+	p.fn_call(mut f, 0, '', '')
+	p.is_c_fn_call = false
+	// Try looking it up. Maybe its defined with "C.fn_name() fn_type",
+	// then we know what type it returns
+	cfn := p.table.find_fn(name) or {
+		// Not Found? Return 'void*'
+		//return 'cvoid' //'void*'
+		if false {
+		p.warn('\ndefine imported C function with ' +
+			'`fn C.$name([args]) [return_type]`\n')
+		}
+		return 'void*'
+	}
+	// println("C fn $name has type $cfn.typ")
+	return cfn.typ
+}
+
+fn (p mut Parser) get_undefined_fn_type(name string, orig_name string) string {
+	if p.first_pass() {
+		p.next()
+		// First pass, the function can be defined later.
+		return 'void'
+	} else {
+		// We are in the second pass, that means this function was not defined, throw an error.
+
+		// V script? Try os module.
+		// TODO
+		if p.v_script {
+			//name = name.replace('main__', 'os__')
+			//f = p.table.find_fn(name)
+		}
+
+		// check for misspelled function / variable / module
+		suggested := p.identify_typo(name, p.import_table)
+		if suggested != '' {
+			p.error('undefined function: `$name`. did you mean: `$suggested`')
+		}
+
+		// If orig_name is a mod, then printing undefined: `mod` tells us nothing
+		// if p.table.known_mod(orig_name) {
+		if p.table.known_mod(orig_name) || p.import_table.known_alias(orig_name) {
+			m_name := mod_gen_name_rev(name.replace('__', '.'))
+			p.error('undefined function: `$m_name` (in module `$orig_name`)')
+		} else if orig_name in reserved_type_param_names {
+			p.error('the letter `$orig_name` is reserved for type parameters')
+		} else {
+			p.error('undefined symbol: `$orig_name`')
+		}
+		return 'void'
+	}
+}
+
 fn (p mut Parser) var_expr(v Var) string {
 	//p.log('\nvar_expr() v.name="$v.name" v.typ="$v.typ"')
 	// println('var expr is_tmp=$p.cgen.is_tmp\n')
@@ -2088,11 +2121,6 @@ fn (p mut Parser) var_expr(v Var) string {
 	return typ
 }
 
-// for debugging only
-fn (p &Parser) fileis(s string) bool {
-	return p.scanner.file_path.contains(s)
-}
-
 // user.name => `str_typ` is `User`
 // user.company.name => `str_typ` is `Company`
 fn (p mut Parser) dot(str_typ_ string, method_ph int) string {
@@ -2203,7 +2231,7 @@ struct $typ.name {
 		p.error_with_token_index('could not find method `$field_name`', fname_tidx) // should never happen
 		exit(1)
 	}
-	p.fn_call(method, method_ph, '', str_typ)
+	p.fn_call(mut method, method_ph, '', str_typ)
 	// Methods returning `array` should return `array_string`
 	if method.typ == 'array' && typ.name.starts_with('array_') {
 		return typ.name
@@ -2404,6 +2432,11 @@ struct IndexCfg {
 
 }
 
+// for debugging only
+fn (p &Parser) fileis(s string) bool {
+	return p.scanner.file_path.contains(s)
+}
+
 // in and dot have higher priority than `!`
 fn (p mut Parser) indot_expr() string {
 	ph := p.cgen.add_placeholder()
@@ -3905,6 +3938,7 @@ fn (p mut Parser) return_st() {
 		is_none := p.tok == .key_none
 		p.expected_type = p.cur_fn.typ
 		mut expr_type := p.bool_expression()
+		// println('$p.cur_fn.name returns type $expr_type, should be $p.cur_fn.typ')
 		mut types := []string
 		mut mr_values := [p.cgen.cur_line.right(ph).trim_space()]
 		types << expr_type
diff --git a/vlib/compiler/table.v b/vlib/compiler/table.v
index 8f780b8ec0..5e44f92330 100644
--- a/vlib/compiler/table.v
+++ b/vlib/compiler/table.v
@@ -12,7 +12,6 @@ mut:
 	typesmap     map[string]Type
 	consts       []Var
 	fns          map[string]Fn
-	generic_fns  []GenTable //map[string]GenTable // generic_fns['listen_and_serve'] == ['Blog', 'Forum']
 	obf_ids      map[string]int // obf_ids['myfunction'] == 23
 	modules      []string // List of all modules registered by the application
 	imports      []string // List of all imports
@@ -40,12 +39,6 @@ enum NameCategory {
 struct Name {
 	cat NameCategory
 	idx int // e.g. typ := types[name.idx]
-}	
-
-struct GenTable {
-	fn_name string
-mut:
-	types []string
 }
 
 // Holds import information scoped to the parsed file
@@ -125,7 +118,7 @@ mut:
 	// This information is needed in the first pass.
 	is_placeholder bool
 	gen_str	       bool  // needs `.str()` method generation
-	
+
 }
 
 struct TypeNode {
@@ -218,6 +211,7 @@ fn (t &Table) debug_fns() string {
 const (
 	number_types = ['number', 'int', 'i8', 'i16', 'u16', 'u32', 'byte', 'i64', 'u64', 'f32', 'f64']
 	float_types  = ['f32', 'f64']
+	reserved_type_param_names = ['R', 'S', 'T', 'U', 'W']
 )
 
 fn is_number_type(typ string) bool {
@@ -254,8 +248,10 @@ fn new_table(obfuscate bool) &Table {
 	t.register_type('bool')
 	t.register_type('void')
 	t.register_type('voidptr')
-	t.register_type('T')
 	t.register_type('va_list')
+	for c in reserved_type_param_names {
+		t.register_type(c)
+	}
 	t.register_const('stdin', 'int', 'main')
 	t.register_const('stdout', 'int', 'main')
 	t.register_const('stderr', 'int', 'main')
@@ -585,6 +581,13 @@ fn (p mut Parser) check_types2(got_, expected_ string, throw bool) bool {
 	if p.pref.translated {
 		return true
 	}
+
+	// generic return type
+	if expected == '_ANYTYPE_' {
+		p.cur_fn.typ = got
+		return true
+	}
+
 	// variadic
 	if expected.starts_with('...') {
 		expected = expected.right(3)
@@ -665,7 +668,7 @@ fn (p mut Parser) check_types2(got_, expected_ string, throw bool) bool {
 	if got.starts_with('fn ') && (expected.ends_with('fn') ||
 	expected.ends_with('Fn')) {
 		return true
-	}	
+	}
 	// Allow pointer arithmetic
 	if expected=='void*' && got=='int' {
 		return true
@@ -676,7 +679,7 @@ fn (p mut Parser) check_types2(got_, expected_ string, throw bool) bool {
 	//}
 	if is_number_type(got) && is_number_type(expected) && p.is_const_literal {
 		return true
-	}	
+	}
 	expected = expected.replace('*', '')
 	got = got.replace('*', '')
 	if got != expected {
@@ -749,7 +752,7 @@ fn (t &Table) has_at_least_one_test_fn() bool {
 	for _, f in t.fns {
 		if f.name.starts_with('main__test_') {
 			return true
-		}	
+		}
 	}
 	return false
 }
@@ -778,7 +781,7 @@ fn (table &Table) cgen_name_type_pair(name, typ string) string {
 	else if typ.starts_with('fn (') {
 		T := table.find_type(typ)
 		if T.name == '' {
-			println('this should never happen')
+			eprintln('function type `$typ` not found')
 			exit(1)
 		}
 		str_args := T.func.str_args(table)
@@ -811,32 +814,6 @@ fn is_valid_int_const(val, typ string) bool {
 	return true
 }
 
-fn (t mut Table) register_generic_fn(fn_name string) {
-	t.generic_fns << GenTable{fn_name, []string}
-}
-
-fn (t &Table) fn_gen_types(fn_name string) []string {
-	for _, f in t.generic_fns {
-		if f.fn_name == fn_name {
-			return f.types
-		}
-	}
-	verror('function $fn_name not found')
-	return []string
-}
-
-// `foo<Bar>()`
-// fn_name == 'foo'
-// typ == 'Bar'
-fn (t mut Table) register_generic_fn_type(fn_name, typ string) {
-	for i, f in t.generic_fns {
-		if f.fn_name == fn_name {
-			t.generic_fns[i].types << typ
-			return
-		}
-	}
-}
-
 fn (p mut Parser) typ_to_fmt(typ string, level int) string {
 	t := p.table.find_type(typ)
 	if t.cat == .enum_ {
@@ -866,6 +843,11 @@ fn (p mut Parser) typ_to_fmt(typ string, level int) string {
 	return ''
 }
 
+fn type_to_safe_str(typ string) string {
+	r := typ.replace(' ','').replace('(','_').replace(')','_')
+	return r
+}
+
 fn is_compile_time_const(s_ string) bool {
 	s := s_.trim_space()
 	if s == '' {
diff --git a/vlib/compiler/tests/generic_test.v b/vlib/compiler/tests/generic_test.v
new file mode 100644
index 0000000000..9c7ace8db1
--- /dev/null
+++ b/vlib/compiler/tests/generic_test.v
@@ -0,0 +1,58 @@
+fn simple<T>(p T) T {
+    return p
+}
+
+fn sum<T>(l []T, nil T) T {
+    mut r := nil
+    for e in l {
+        r += e
+    }
+    return r
+}
+
+fn map_f<T,U,R>(l []T, f fn(T)U) []U {
+    mut r := []U
+    for e in l {
+        r << f(e)
+    }
+    return r
+}
+
+fn foldl<T>(l []T, nil T, f fn(T,T)T) T {
+    mut r := nil
+    for e in l {
+        r = f(r, e)
+    }
+    return r
+}
+
+fn plus<T>(a T, b T) T {
+    return a+b
+}
+
+fn square(x int) int {
+    return x*x
+}
+
+fn mul_int(x int, y int) int {
+    return x*y
+}
+
+fn assert_eq<T>(a, b T) {
+    r := a == b
+    println('$a == $b: ${r.str()}')
+    assert r
+}
+
+fn test_generic_fn() {
+    assert_eq(simple(0+1), 1)
+    assert_eq(simple('g') + 'h', 'gh')
+    assert_eq(sum([5.1,6.2,7.0], 0.0), 18.3)
+    assert_eq(plus(i64(4), i64(6)), i64(10))
+    a := [1,2,3,4]
+    $if !windows {
+        b := map_f(a, square) 
+        assert_eq(sum(b, 0), 30)     // 1+4+9+16 = 30
+        assert_eq(foldl(b, 1, mul_int), 576)   // 1*4*9*16 = 576
+    }
+}
diff --git a/vlib/compiler/tests/print_test.v b/vlib/compiler/tests/print_test.v
new file mode 100644
index 0000000000..ee87ceab0e
--- /dev/null
+++ b/vlib/compiler/tests/print_test.v
@@ -0,0 +1,3 @@
+fn test_print() {
+    println(2.0)
+}
diff --git a/vlib/compiler/tests/repl/error.repl b/vlib/compiler/tests/repl/error.repl
index 715b2e07de..0f806dae68 100644
--- a/vlib/compiler/tests/repl/error.repl
+++ b/vlib/compiler/tests/repl/error.repl
@@ -1,3 +1,3 @@
 println(a)
 ===output===
-.vrepl.v:2:9: undefined: `a`
+.vrepl.v:2:9: undefined symbol: `a`
diff --git a/vlib/compiler/tests/repl/error_nosave.repl b/vlib/compiler/tests/repl/error_nosave.repl
index fb6a5158b5..fb009d92e1 100644
--- a/vlib/compiler/tests/repl/error_nosave.repl
+++ b/vlib/compiler/tests/repl/error_nosave.repl
@@ -1,5 +1,5 @@
 a
 33
 ===output===
-.vrepl_temp.v:3:9: undefined: `a`
+.vrepl_temp.v:3:9: undefined symbol: `a`
 33