Add examples of planned features (#401)

* Add examples for planned features

* Make example syntax more consistent

* Add gadts examples with functional dependencies

* Make example syntax more consistent

* Chmod examples for the interpreter

* Add shebangs

* Add instances examples

examples/contexts.tk

@@ -0,0 +1,27 @@
+#!/usr/bin/env tako
+
+test() = {
+  allocator = import("allocator")
+  ptr = allocator.allocate(sizeof(Char[100]))
+  if (ptr == nullptr) {
+    print("Success")
+    exit(0)
+  } else {
+    print("Failure")
+  }
+}
+
+main() = {
+  allocator = import("allocator")
+  logger = import("logger")
+
+  test_logger = logger.new_logger()
+  with {
+    allocator.allocate = allocator.report_oom,
+    system.out = test_logger,
+    system.error = test_logger,
+    run = test
+  }
+
+  print(test_logger)
+}

examples/enums.tk

@@ -0,0 +1,27 @@
+#!/usr/bin/env tako
+
+boolean = Enum.new(
+  true=1,
+  false=0,
+)
+
+boolean.import_literals()
+
+color = Enum
+  .based_on(
+    byte[3]
+  )
+  .open(
+    red=#ff0000,
+    green=#00ff00,
+    blue=#0000ff,
+  )
+
+color.add_values(
+  purple=#ff00ff,
+  cyan=#00ffff,
+)
+
+main() = {
+  print("Color {red} is red")
+}

examples/fib.tk

@@ -1,3 +1,5 @@
-fib<T: Nat>(n: T): T=if(n<=1, 1, fib(n-1)+fib(n-2));
+#!/usr/bin/env tako
+
+fib(n: T, {T: Nat}): T=if(n<=1, 1, fib(n-1)+fib(n-2))
 
 print(fib(80))

examples/fib_acc.tk

@@ -0,0 +1,7 @@
+#!/usr/bin/env tako
+
+fib_helper(n: T, a: T, b: T, {T: Nat}): T=if(n==0, a, fib_helper(n-1, b, a+b))
+
+fib(n: T, {T: Nat}): T=fib_helper(n, 0, 1)
+
+print(fib(80))

examples/generic_abstract_data_types.tk

@@ -0,0 +1,35 @@
+#!/usr/bin/env tako
+
+// A simple, untyped  implementation of S expressions.
+SExpr: Type = struct.new(
+  func: (args: Value[n]),
+  args: SExpr[n],
+  {n: Int},
+)
+
+// A well typed, but little, language using GADTs.
+Expr(
+  SubExpr(R: AllowedType): Reference(Expr(SubExpr, R))=Expr,
+  R: AllowedType,
+  with {AllowedType = Integer|Boolean}
+) = gadt.new(
+
+  // Control flow:
+  if(
+    cond: SubExpr(R=Boolean),
+    then: SubExpr(R=T),
+    else: SubExpr(R=T),
+    {T: AllowedType}
+  ): Expr(SubExpr, R=T),
+
+  // Binary operations:
+  or     (left:  SubExpr(R=Boolean), right: SubExpr(R=Boolean)): Expr(SubExpr, R=Boolean),
+  and    (left:  SubExpr(R=Boolean), right: SubExpr(R=Boolean)): Expr(SubExpr, R=Boolean),
+  add    (left:  SubExpr(R=Integer), right: SubExpr(R=Integer)): Expr(SubExpr, R=Integer),
+  mul    (left:  SubExpr(R=Integer), right: SubExpr(R=Integer)): Expr(SubExpr, R=Integer),
+  eq     (left:  SubExpr(R=Integer), right: SubExpr(R=Integer)): Expr(SubExpr, R=Boolean),
+
+  // Constants:
+  integer(value: Integer): Expr(SubExpr, R=Integer),
+  boolean(value: Boolean): Expr(SubExpr, R=Boolean),
+)

examples/instances.tk

@@ -0,0 +1,44 @@
+Bounded = Enum
+  .open()
+  .based_on({
+    min: (T: Type): T,
+    max: (T: Type): T,
+  })
+
+Bounded.add_values(
+  boolean = {
+    min(T)=false,
+    max(T)=true,
+  }
+  integer = {
+    min(T)=0,
+    max(T)=2**64-1,
+  }
+)
+
+Showable = Enum.based_on({
+  to_string: (t: Type): String
+}).open()
+
+print(t: Type, {end: String="\n"}): String = system.out.write(t.to_string()+end)
+
+to_base(value: integer, {base: integer=10}) = {
+  out: Char[math.log(Integer.max, base)]="0";
+  i: integer = 0;
+  while(
+    cond = t > 0,
+    loop = {
+      out[-i] = value%10,
+      value=value/10,
+      i=i+1
+    },
+    result = out[-i..],
+  )
+}
+
+Showable.add_values(
+  char(t: Char)=String.from_chars([t]),
+  chars(t: Char[n], {n: Integer})=String.from_chars(t),
+  string(t: String)=t,
+  integer(t: Integer)=t.to_base(base=10)
+)

examples/vector_transpose.tk

@@ -1,3 +1,5 @@
+#!/usr/bin/env tako
+
 main = {
   x3by2 = Vector.new([
       [ 0, 1 ],

examples/vector_transpose_failing.tk

@@ -1,4 +1,6 @@
-main = {
+#!/usr/bin/env tako
+
+main() = {
   x3by2 = Vector.new([
       [ 0, 1 ],
       [ 2, 3 ],