Prelude extension (#268)

- Adds `min` and `max` functions
- Adds `strListCat` for efficient string concatenation and `replicate` for string repetition
- Exposes fst and snd as methods on pairs
- Adds map method to Option type

Author: wojpok

lib/Base/Option.fram

@@ -31,3 +31,10 @@ pub method unwrap {~__line__, ~__file__, ?msg} self =
   | None   => runtimeError (msg.unwrapOr "Called `unwrap` on `None`")
   | Some x => x
   end
+
+{## Maps value stored in `Some`. ##}
+pub method map self f =
+  match self with
+  | None   => None
+  | Some x => Some (f x)
+  end

lib/Prelude.fram

@@ -23,7 +23,9 @@ pub let id x = x
 pub let flip f x y = f y x
 
 pub let fst (x, _) = x
+pub method fst = fst
 pub let snd (_, y) = y
+pub method snd = snd
 
 pub let not b = if b then False else True
 
@@ -48,3 +50,25 @@ pub module Int64
   pub let one  = 1L
   pub let ofInt (n : Int) = n.toInt64
 end
+
+## Returns the greater of two elements `x` and `y`.
+pub let max {T, method lt : T -> T ->> Bool} (x : T) (y : T) =
+  if y < x then x else y
+
+## Returns the smaller of two elements `x` and `y`.
+pub let min {T, method lt : T -> T ->> Bool} (x : T) (y : T) =
+  if y < x then y else x
+
+## Concatenates list of strings in linear time.
+pub let strListCat = extern dbl_strListCat : List String -> String
+
+## Creates a string with `n` repetitions.
+pub let rec replicate (s : String) (n : Int) = 
+  if n <= 0 then
+    ""
+  else if n % 2 == 0 then
+   (let s' = replicate s (n / 2) in
+    s' + s')
+  else
+   (let s' = replicate s (n / 2) in
+    s' + (s' + s))

test/stdlib/stdlib0001_Option.fram

@@ -4,4 +4,5 @@ let _ =
   assert ((Some 42).unwrap == 42);
   let ~onError () = 0 in
   assert ((None).unwrapErr == 0);
-  assert ((Some 42).unwrapErr == 42)
+  assert ((Some 42).unwrapErr == 42);
+  assert (Some 42 >.map (fn x => 1 + x) >.unwrapErr == 43)

test/stdlib/stdlib0006_Prelude.fram

@@ -0,0 +1,28 @@
+# min
+let _ =
+  assert (min 10 20 == 10);
+  assert (min 20 10 == 10);
+  assert (min 10 10 == 10);
+  assert (min "abc" "def" == "abc")
+
+# max
+let _ =
+  assert (max 10 20 == 20);
+  assert (max 20 10 == 20);
+  assert (max 20 20 == 20);
+  assert (max "abc" "def" == "def")
+
+# strListCat
+let _ =
+  assert (strListCat ["a", "b", "c"] == "abc");
+  assert (strListCat ["do", "re", "mi"] == "doremi");
+  assert (strListCat [] == "")
+
+# replicate
+let _ =
+  assert (replicate "ab" 0 == "");
+  assert (replicate "ab" 1 == "ab");
+  assert (replicate "ab" 2 == "abab");
+  assert (replicate "ab" 3 == "ababab");
+  assert (replicate "ab" 5 == "ababababab");
+  assert (replicate "" 20 == "")