diff --git a/README.md b/README.md
index 73e2160..2e9c603 100644
--- a/README.md
+++ b/README.md
@@ -5,12 +5,12 @@ language that cross-compiles to C. Tomo is designed to anticipate and influence
 the language design decisions of the future.
 
 ```
-func greeting(name:Text)->Text
+func greeting(name:Text)->Text:
 	greeting := "hello {name}!"
 	words := greeting:split(" ")
 	return " ":join([w:capitalize() for w in words])
 
-func main(name="World")
+func main(name="World"):
 	to_say := greeting(name)
 	say(to_say)
 ```
diff --git a/parse.c b/parse.c
index e325ebf..e3fdbb4 100644
--- a/parse.c
+++ b/parse.c
@@ -781,8 +781,10 @@ PARSER(parse_reduction) {
     }
 
     ast_t *fallback = NULL;
-    if (match_word(&pos, "else"))
+    if (match_word(&pos, "else")) {
+        expect_str(ctx, start, &pos, ":", "I expected a ':' here");
         fallback = expect(ctx, pos-4, &pos, parse_expr, "I couldn't parse the expression after this 'else'");
+    }
 
     return NewAST(ctx->file, start, pos, Reduction, .iter=iter, .combination=combination, .fallback=fallback);
 }
@@ -838,7 +840,7 @@ PARSER(parse_if) {
     if (!condition) condition = expect(ctx, start, &pos, parse_expr,
                                        "I expected to find an expression for this 'if'");
 
-    match_word(&pos, "then"); // optional
+    expect_str(ctx, start, &pos, ":", "I expected a ':' here");
 
     ast_t *body = expect(ctx, start, &pos, parse_opt_indented_block, "I expected a body for this 'if' statement"); 
 
@@ -848,6 +850,7 @@ PARSER(parse_if) {
     const char *else_start = pos;
     if (get_indent(ctx->file, tmp) == starting_indent && match_word(&tmp, "else")) {
         pos = tmp;
+        expect_str(ctx, start, &pos, ":", "I expected a ':' here");
         else_body = expect(ctx, else_start, &pos, parse_opt_indented_block, "I expected a body for this 'else'"); 
     }
     return NewAST(ctx->file, start, pos, If, .condition=condition, .body=body, .else_body=else_body);
@@ -881,7 +884,8 @@ PARSER(parse_when) {
             var = NULL;
         }
 
-        match_word(&pos, "then"); // optional
+        expect_str(ctx, start, &pos, ":", "I expected a ':' here");
+
         ast_t *body = expect(ctx, start, &pos, parse_opt_indented_block, "I expected a body for this 'when' clause"); 
         clauses = new(when_clause_t, .var=var, .tag_name=tag_name, .body=body, .next=clauses);
         tmp = pos;
@@ -893,6 +897,7 @@ PARSER(parse_when) {
     const char *else_start = pos;
     if (get_indent(ctx->file, tmp) == starting_indent && match_word(&tmp, "else")) {
         pos = tmp;
+        expect_str(ctx, start, &pos, ":", "I expected a ':' here");
         else_body = expect(ctx, else_start, &pos, parse_opt_indented_block, "I expected a body for this 'else'"); 
     }
     return NewAST(ctx->file, start, pos, When, .subject=subject, .clauses=clauses, .else_body=else_body);
@@ -911,6 +916,7 @@ PARSER(parse_for) {
     }
     expect_str(ctx, start, &pos, "in", "I expected an 'in' for this 'for'");
     ast_t *iter = expect(ctx, start, &pos, parse_expr, "I expected an iterable value for this 'for'");
+    expect_str(ctx, start, &pos, ":", "I expected a ':' here");
     match(&pos, "do"); // optional
     ast_t *body = expect(ctx, start, &pos, parse_opt_indented_block, "I expected a body for this 'for'"); 
 
@@ -919,6 +925,7 @@ PARSER(parse_for) {
     ast_t *empty = NULL;
     if (match_word(&else_start, "else") && get_indent(ctx->file, else_start) == starting_indent) {
         pos = else_start;
+        expect_str(ctx, start, &pos, ":", "I expected a ':' here");
         empty = expect(ctx, pos, &pos, parse_opt_indented_block, "I expected a body for this 'else'");
     }
     return NewAST(ctx->file, start, pos, For, .index=value ? index : NULL, .value=value ? value : index, .iter=iter, .body=body, .empty=empty);
@@ -929,7 +936,7 @@ PARSER(parse_while) {
     const char *start = pos;
     if (!match_word(&pos, "while")) return NULL;
     ast_t *condition = expect(ctx, start, &pos, parse_expr, "I don't see a viable condition for this 'while'");
-    match(&pos, "do"); // optional
+    expect_str(ctx, start, &pos, ":", "I expected a ':' here");
     ast_t *body = expect(ctx, start, &pos, parse_opt_indented_block, "I expected a body for this 'while'"); 
     const char *tmp = pos;
     whitespace(&tmp);
@@ -1603,7 +1610,7 @@ PARSER(parse_file_body) {
 }
 
 PARSER(parse_struct_def) {
-    // struct Foo(...) \n body
+    // struct Foo(...) [: \n body]
     const char *start = pos;
     if (!match_word(&pos, "struct")) return NULL;
 
@@ -1636,13 +1643,15 @@ PARSER(parse_struct_def) {
 
     expect_closing(ctx, &pos, ")", "I wasn't able to parse the rest of this struct");
 
-    const char *ns_pos = pos;
-    whitespace(&ns_pos);
-    int64_t ns_indent = get_indent(ctx->file, ns_pos);
     ast_t *namespace = NULL;
-    if (ns_indent > starting_indent) {
-        pos = ns_pos;
-        namespace = optional(ctx, &pos, parse_namespace);
+    if (match(&pos, ":")) {
+        const char *ns_pos = pos;
+        whitespace(&ns_pos);
+        int64_t ns_indent = get_indent(ctx->file, ns_pos);
+        if (ns_indent > starting_indent) {
+            pos = ns_pos;
+            namespace = optional(ctx, &pos, parse_namespace);
+        }
     }
     if (!namespace)
         namespace = NewAST(ctx->file, pos, pos, Block, .statements=NULL);
@@ -1650,7 +1659,7 @@ PARSER(parse_struct_def) {
 }
 
 ast_t *parse_enum_def(parse_ctx_t *ctx, const char *pos) {
-    // tagged union: enum Foo[a, b(x:Int,y:Int)=5, ...] \n namespace
+    // tagged union: enum Foo(a, b(x:Int,y:Int)=5, ...) [: \n namespace]
     const char *start = pos;
     if (!match_word(&pos, "enum")) return NULL;
     int64_t starting_indent = get_indent(ctx->file, pos);
@@ -1713,13 +1722,15 @@ ast_t *parse_enum_def(parse_ctx_t *ctx, const char *pos) {
 
     REVERSE_LIST(tags);
 
-    const char *ns_pos = pos;
-    whitespace(&ns_pos);
-    int64_t ns_indent = get_indent(ctx->file, ns_pos);
     ast_t *namespace = NULL;
-    if (ns_indent > starting_indent) {
-        pos = ns_pos;
-        namespace = optional(ctx, &pos, parse_namespace);
+    if (match(&pos, ":")) {
+        const char *ns_pos = pos;
+        whitespace(&ns_pos);
+        int64_t ns_indent = get_indent(ctx->file, ns_pos);
+        if (ns_indent > starting_indent) {
+            pos = ns_pos;
+            namespace = optional(ctx, &pos, parse_namespace);
+        }
     }
     if (!namespace)
         namespace = NewAST(ctx->file, pos, pos, Block, .statements=NULL);
@@ -1729,7 +1740,7 @@ ast_t *parse_enum_def(parse_ctx_t *ctx, const char *pos) {
 
 PARSER(parse_lang_def) {
     const char *start = pos;
-    // lang Name [namespace...]
+    // lang Name: [namespace...]
     if (!match_word(&pos, "lang")) return NULL;
     int64_t starting_indent = get_indent(ctx->file, pos);
     spaces(&pos);
@@ -1738,13 +1749,15 @@ PARSER(parse_lang_def) {
         parser_err(ctx, start, pos, "I expected a name for this lang");
     spaces(&pos);
 
-    const char *ns_pos = pos;
-    whitespace(&ns_pos);
-    int64_t ns_indent = get_indent(ctx->file, ns_pos);
     ast_t *namespace = NULL;
-    if (ns_indent > starting_indent) {
-        pos = ns_pos;
-        namespace = optional(ctx, &pos, parse_namespace);
+    if (match(&pos, ":")) {
+        const char *ns_pos = pos;
+        whitespace(&ns_pos);
+        int64_t ns_indent = get_indent(ctx->file, ns_pos);
+        if (ns_indent > starting_indent) {
+            pos = ns_pos;
+            namespace = optional(ctx, &pos, parse_namespace);
+        }
     }
     if (!namespace)
         namespace = NewAST(ctx->file, pos, pos, Block, .statements=NULL);
@@ -1843,9 +1856,10 @@ PARSER(parse_func_def) {
 
     type_ast_t *ret_type = NULL;
     spaces(&pos);
-    if (match(&pos, "->") || match(&pos, ":"))
+    if (match(&pos, "->"))
         ret_type = optional(ctx, &pos, parse_type);
 
+    expect_str(ctx, start, &pos, ":", "I expected a ':' here");
     ast_t *body = expect(ctx, start, &pos, parse_opt_indented_block,
                              "This function needs a body block");
     return NewAST(ctx->file, start, pos, FunctionDef,
diff --git a/test/arrays.tm b/test/arrays.tm
index be767fa..de1771b 100644
--- a/test/arrays.tm
+++ b/test/arrays.tm
@@ -1,9 +1,9 @@
-func main()
-	if yes
+func main():
+	if yes:
 		>> [:Num32]
 		= [] : [Num32]
 
-	if yes
+	if yes:
 		>> arr := [10, 20, 30]
 		= [10, 20, 30]
 
@@ -16,18 +16,18 @@ func main()
 		= 3
 
 		sum := 0
-		for x in arr
+		for x in arr:
 			sum += x
 		>> sum
 		= 60
 
 		str := ""
-		for i,x in arr
+		for i,x in arr:
 			str ++= "({i},{x})"
 		>> str
 		= "(1,10)(2,20)(3,30)"
 
-	if yes
+	if yes:
 		>> arr := [10, 20] ++ [30, 40]
 		= [10, 20, 30, 40]
 
@@ -39,7 +39,7 @@ func main()
 		>> arr
 		= [10, 20, 30, 40, 50, 60, 70]
 
-	if yes
+	if yes:
 		>> arr := [10, 20]
 		>> copy := arr
 		>> arr ++= 30
@@ -48,7 +48,7 @@ func main()
 		>> copy
 		= [10, 20]
 
-	if yes
+	if yes:
 		>> [10*i for i in 5]
 		= [10, 20, 30, 40, 50]
 
@@ -61,7 +61,7 @@ func main()
 	>> [x for x in y if x > 1 for y in [3, 4, 5] if y < 5]
 	= [2, 3, 2, 3, 4]
 
-	if yes
+	if yes:
 		>> arr := @[10, 20]
 		>> copy := arr[]
 		>> arr:insert(30)
@@ -70,12 +70,12 @@ func main()
 		>> copy
 		= [10, 20]
 
-	if yes
+	if yes:
 		>> arr := [10, 20, 30]
 		>> arr:reversed()
 		= [30, 20, 10]
 
-	if yes
+	if yes:
 		>> nums := [10, -20, 30]
 		// Sorted function doesn't mutate original:
 		>> nums:sorted()
@@ -96,20 +96,20 @@ func main()
 
 	>> ["A", "B", "C"]:sample(10, [1.0, 0.5, 0.0])
 
-	if yes
+	if yes:
 		>> heap := [Int.random(max=50) for _ in 10]
 		>> heap:heapify()
 		>> heap
 		sorted := [:Int]
-		while #heap > 0
+		while #heap > 0:
 			sorted:insert(heap:heap_pop())
 		>> sorted == sorted:sorted()
 		= yes
-		for _ in 10
+		for _ in 10:
 			heap:heap_push(Int.random(max=50))
 		>> heap
 		sorted = [:Int]
-		while #heap > 0
+		while #heap > 0:
 			sorted:insert(heap:heap_pop())
 		>> sorted == sorted:sorted()
 		= yes
diff --git a/test/corecursive_func.tm b/test/corecursive_func.tm
index 22ffd62..a5c13dd 100644
--- a/test/corecursive_func.tm
+++ b/test/corecursive_func.tm
@@ -1,15 +1,15 @@
-func ping(x:Int)->[Text]
-	if x > 0
+func ping(x:Int)->[Text]:
+	if x > 0:
 		return ["ping: {x}"] ++ pong(x-1)
-	else
+	else:
 		return ["ping: {x}"]
 
-func pong(x:Int)->[Text]
-	if x > 0
+func pong(x:Int)->[Text]:
+	if x > 0:
 		return ["pong: {x}"] ++ ping(x-1)
-	else
+	else:
 		return ["pong: {x}"]
 
-func main()
+func main():
 	>> ping(3)
 	= ["ping: 3", "pong: 2", "ping: 1", "pong: 0"]
diff --git a/test/enums.tm b/test/enums.tm
index c06862a..1bc2620 100644
--- a/test/enums.tm
+++ b/test/enums.tm
@@ -1,6 +1,6 @@
 enum Foo(Zero, One(x:Int), Two(x,y:Int))
 
-func main()
+func main():
 	>> Foo.Zero
 	= Foo.Zero
 	>> Foo.One(123)
@@ -27,9 +27,9 @@ func main()
 	>> t[Foo.Zero]
 	= "missing"
 
-	when x is o:One
+	when x is o:One:
 		>> o.x
 		= 123
-	else
+	else:
 		fail("Oops")
 
diff --git a/test/extern.tm b/test/extern.tm
index 896c573..da3b182 100644
--- a/test/extern.tm
+++ b/test/extern.tm
@@ -1,5 +1,5 @@
 extern CORD_cat:func(a:Text, b:Text)->Text
 
-func main()
+func main():
 	>> CORD_cat("hello ", "world")
 	= "hello world"
diff --git a/test/for.tm b/test/for.tm
index 6365638..a050c89 100644
--- a/test/for.tm
+++ b/test/for.tm
@@ -1,35 +1,35 @@
 
-func all_nums(nums:[Int])->Text
+func all_nums(nums:[Int])->Text:
 	result := ""
-	for num in nums
+	for num in nums:
 		result ++= "{num},"
-	else
+	else:
 		return "EMPTY"
 	return result
 
-func labeled_nums(nums:[Int])->Text
+func labeled_nums(nums:[Int])->Text:
 	result := ""
-	for i,num in nums
+	for i,num in nums:
 		result ++= "{i}:{num},"
-	else
+	else:
 		return "EMPTY"
 	return result
 
-func table_str(t:{Text:Text})->Text
+func table_str(t:{Text:Text})->Text:
 	str := ""
-	for k,v in t
+	for k,v in t:
 		str ++= "{k}:{v},"
-	else return "EMPTY"
+	else: return "EMPTY"
 	return str
 
-func table_key_str(t:{Text:Text})->Text
+func table_key_str(t:{Text:Text})->Text:
 	str := ""
-	for k in t
+	for k in t:
 		str ++= "{k},"
-	else return "EMPTY"
+	else: return "EMPTY"
 	return str
 
-func main()
+func main():
 	>> all_nums([10,20,30])
 	= "10,20,30,"
 	>> all_nums([:Int])
diff --git a/test/functions.tm b/test/functions.tm
index 13cdee5..426c33b 100644
--- a/test/functions.tm
+++ b/test/functions.tm
@@ -1,10 +1,10 @@
-func add(x:Int, y:Int)->Int
+func add(x:Int, y:Int)->Int:
 	return x + y
 
-func cached_heap(x:Int; cached)->@Int
+func cached_heap(x:Int; cached)->@Int:
 	return @x
 
-func main()
+func main():
 	>> add(3, 5)
 	= 8
 
diff --git a/test/integers.tm b/test/integers.tm
index 9b573aa..94ab8ac 100644
--- a/test/integers.tm
+++ b/test/integers.tm
@@ -1,4 +1,4 @@
-func main()
+func main():
 	>> 2 + 3
 	= 5
 
@@ -27,7 +27,7 @@ func main()
 	= 1
 
 	nums := ""
-	for x in 5
+	for x in 5:
 		nums ++= "{x},"
 	>> nums
 	= "1,2,3,4,5,"
diff --git a/test/lambdas.tm b/test/lambdas.tm
index a445540..0ec0826 100644
--- a/test/lambdas.tm
+++ b/test/lambdas.tm
@@ -1,13 +1,13 @@
-func make_adder(x:Int)-> func(y:Int)->Int
+func make_adder(x:Int)-> func(y:Int)->Int:
 	return func(y:Int) x + y
 
-func suffix_fn(fn:func(t:Text)->Text, suffix:Text)->func(t:Text)->Text
+func suffix_fn(fn:func(t:Text)->Text, suffix:Text)->func(t:Text)->Text:
 	return func(t:Text) fn(t)++suffix
 
-func mul_func(n:Int, fn:func(x:Int)->Int)-> func(x:Int)->Int
+func mul_func(n:Int, fn:func(x:Int)->Int)-> func(x:Int)->Int:
 	return func(x:Int) n*fn(x)
 
-func main()
+func main():
 	>> add_one := func(x:Int) x + 1
 	>> add_one(10)
 	= 11
diff --git a/test/lang.tm b/test/lang.tm
index ad09b60..3dea6de 100644
--- a/test/lang.tm
+++ b/test/lang.tm
@@ -1,6 +1,6 @@
-lang HTML
+lang HTML:
 	HEADER := $HTML{}"<!DOCTYPE HTML>"
-	func escape(t:Text)->HTML
+	func escape(t:Text)->HTML:
 		t = t:replace("&", "&amp;")
 		t = t:replace("<", "&lt;")
 		t = t:replace(">", "&gt;")
@@ -8,13 +8,13 @@ lang HTML
 		t = t:replace("'", "&#39;")
 		return HTML.from_unsafe_text(t)
 
-	func escape_int(i:Int)->HTML
+	func escape_int(i:Int)->HTML:
 		return HTML.from_unsafe_text("{i}")
 	
-	func paragraph(content:HTML)->HTML
+	func paragraph(content:HTML)->HTML:
 		return $HTML{}"<p>{content}</p>"
 
-func main()
+func main():
 	>> HTML.HEADER
 	= $HTML"<!DOCTYPE HTML>"
 
diff --git a/test/minmax.tm b/test/minmax.tm
index c3af68d..c2f070f 100644
--- a/test/minmax.tm
+++ b/test/minmax.tm
@@ -1,9 +1,9 @@
 
-struct Foo(x:Int, y:Int)
-	func len(f:Foo)->Num
+struct Foo(x:Int, y:Int):
+	func len(f:Foo)->Num:
 		return Num.sqrt(f.x*f.x + f.y*f.y)
 
-func main()
+func main():
 	>> 3 _min_ 5
 	= 3
 	>> 5 _min_ 3
diff --git a/test/nums.tm b/test/nums.tm
index 4e9c81a..9495974 100644
--- a/test/nums.tm
+++ b/test/nums.tm
@@ -1,4 +1,4 @@
-func main()
+func main():
 	>> n := 1.5
 	= 1.5
 
diff --git a/test/reductions.tm b/test/reductions.tm
index 6ed7823..97ec4af 100644
--- a/test/reductions.tm
+++ b/test/reductions.tm
@@ -1,6 +1,6 @@
 struct Foo(x,y:Int)
 
-func main()
+func main():
 	>> (+) [10, 20, 30]
 	= 60
 
diff --git a/test/structs.tm b/test/structs.tm
index 9fe2f6a..840ee84 100644
--- a/test/structs.tm
+++ b/test/structs.tm
@@ -4,7 +4,7 @@ struct Mixed(x:Int, text:Text)
 struct LinkedList(x:Int, next=!LinkedList)
 struct Password(text:Text; secret)
 
-func test_literals()
+func test_literals():
 	>> x := Pair(10, 20)
 	= Pair(x=10, y=20)
 	>> y := Pair(y=20, 10)
@@ -14,7 +14,7 @@ func test_literals()
 	>> x == Pair(-1, -2)
 	= no
 
-func test_metamethods()
+func test_metamethods():
 	>> x := Pair(10, 20)
 	>> y := Pair(100, 200)
 	>> x == y
@@ -32,7 +32,7 @@ func test_metamethods()
 	>> t2[y]
 	= "missing"
 
-func test_mixed()
+func test_mixed():
 	>> x := Mixed(10, "Hello")
 	>> y := Mixed(99, "Hello")
 	>> x == y
@@ -49,7 +49,7 @@ func test_mixed()
 	>> t[y]
 	= "missing"
 
-func main()
+func main():
 	test_literals()
 	test_metamethods()
 	test_mixed()
diff --git a/test/tables.tm b/test/tables.tm
index 2ba4271..8609e52 100644
--- a/test/tables.tm
+++ b/test/tables.tm
@@ -1,4 +1,4 @@
-func main()
+func main():
 	>> t := {"one":1, "two":2; default=999}
 	= {"one":1, "two":2; default=999}
 
@@ -10,7 +10,7 @@ func main()
 	= 999
 
 	t_str := ""
-	for k,v in t
+	for k,v in t:
 		t_str ++= "({k}:{v})"
 	>> t_str
 	= "(one:1)(two:2)"
@@ -45,7 +45,7 @@ func main()
 	= ?%{"one":1, "two":2; default=999}
 
 	t2_str := ""
-	for k,v in t2
+	for k,v in t2:
 		t2_str ++= "({k}:{v})"
 	>> t2_str
 	= "(three:3)"
diff --git a/test/text.tm b/test/text.tm
index bb2cc14..9c451b8 100644
--- a/test/text.tm
+++ b/test/text.tm
@@ -1,4 +1,4 @@
-func main()
+func main():
 	>> str := "Hello Amélie!"
 	>> str:upper()
 	= "HELLO AMÉLIE!"
diff --git a/test/use.tm b/test/use.tm
index a759180..95ab3c7 100644
--- a/test/use.tm
+++ b/test/use.tm
@@ -1,9 +1,9 @@
 imported := use ./use_import
 
-func asdf()->imported.ImportedType
+func asdf()->imported.ImportedType:
 	return imported.get_value()
 
-func main()
+func main():
 	>> [:imported.ImportedType]
 	>> asdf()
 	= ImportedType(name="Hello")
diff --git a/test/use_import.tm b/test/use_import.tm
index fb5f71e..3b8e674 100644
--- a/test/use_import.tm
+++ b/test/use_import.tm
@@ -1,7 +1,7 @@
 struct ImportedType(name:Text)
 
-func get_value()->ImportedType
+func get_value()->ImportedType:
 	return ImportedType("Hello")
 
-func main()
+func main():
 	pass