README: add simple demo UI and corresponding program

README.md

@@ -22,6 +22,30 @@ will be helpful in using this library.
 
 This library deprecates [vty-ui](https://github.com/jtdaugherty/vty-ui).
 
+Example
+-------
+
+Here's an example interface that resizes automatically when the terminal
+size changes (see `programs/ReadmeDemo.hs`):
+
+```
+withBorderStyle unicode $
+borderWithLabel (str "Hello!") $
+(center (str "Left") <+> vBorder <+> center (str "Right"))
+```
+
+Result:
+
+```
+┌─────────Hello!─────────┐
+│           │            │
+│           │            │
+│   Left    │   Right    │
+│           │            │
+│           │            │
+└────────────────────────┘
+```
+
 Getting Started
 ---------------
 

brick.cabal

@@ -94,6 +94,18 @@ library
                        template-haskell,
                        deepseq >= 1.3 && < 1.5
 
+executable brick-readme-demo
+  if !flag(demos)
+    Buildable: False
+  hs-source-dirs:      programs
+  ghc-options:         -threaded -Wall -fno-warn-unused-do-bind -O3
+  default-language:    Haskell2010
+  default-extensions:  CPP
+  main-is:             ReadmeDemo.hs
+  build-depends:       base,
+                       brick,
+                       text
+
 executable brick-cache-demo
   if !flag(demos)
     Buildable: False

programs/ReadmeDemo.hs

@@ -0,0 +1,15 @@
+module Main where
+
+import Brick
+import Brick.Widgets.Center
+import Brick.Widgets.Border
+import Brick.Widgets.Border.Style
+
+ui :: Widget ()
+ui =
+    withBorderStyle unicode $
+    borderWithLabel (str "Hello!") $
+    (center (str "Left") <+> vBorder <+> center (str "Right"))
+
+main :: IO ()
+main = simpleMain ui