Add interpretation of statements.

This allows us to bind values and functions,
in the familiar form `name <- stmt`.

Requires a version of `hint` that is not
available on hackage yet.

CHANGELOG.md

@@ -5,7 +5,7 @@
 
 **v2.0.0** — Snapshot release.
 
-* File format upgraded to version `0.2.0.0`. Conversion of old files happens *automatically* when loading them in the application.
+* Upgrade file format to version `0.2.0.0`. Conversion of old files happens *automatically* when loading them in the application.
 * Support different cell types:
     1. 'code' cells -- for source code to be evaluated
     2. 'text' cells -- plain text format
@@ -19,6 +19,10 @@
 
 ### `hyper`, `hyper-extra`, `hyper-haskell-server` packages
 
+**v0.2.0.0**
+
+* Add interpretation of statements. This allows us to bind values and functions to names, in the familiar form `name <- stmt` where `stmt` is an IO action with a result.
+
 **v0.1.0.2** — Bump dependencies for compatibility with GHC 8.2
 
 **v0.1.0.1** — Bump dependencies.

docs/TODO.md

@@ -6,9 +6,6 @@ Immediate
 
 * Level β:
 
-    * Implement `runStmt` function to bind values while doing IO actions.
-      Cannot be implemented by evaluating expressions.
-
     * Implement a way to evaluate cells concurrently.
       We still want to be able to bind variables sequentially.
       Using `forkIO` explicitely would do, but then we can't stop it again.

haskell/hyper-haskell-server/Main.hs

@@ -11,6 +11,8 @@ import Control.DeepSeq
 import Control.Monad
 import Control.Monad.Catch
 import Control.Exception             (AsyncException(UserInterrupt), evaluate)
+import Data.List                     (groupBy)
+import Data.Maybe                    (catMaybes)
 import Data.Typeable
 import Text.Read                     (readMaybe)
 import System.Environment  as System
@@ -23,8 +25,8 @@ import qualified Language.Haskell.Interpreter as Hint
 import           Data.Aeson                    (toJSON, (.=))
 import qualified Data.Aeson            as JSON
 import qualified Data.ByteString.Char8 as B
-import Data.Text   (Text)
-import Data.String (fromString)
+import Data.Text                       as T    (Text, concat)
+import Data.String                             (fromString)
 import Web.Scotty
 
 -- Interpreter
@@ -99,12 +101,40 @@ setImports   hint = run hint . Hint.setImports
 
 loadFiles    hint = run hint . Hint.loadModules . filter (not . null)
 
-eval         hint expr = run hint $ do
-    -- NOTE: We wrap results into an implicit call to Hyper.display
-    m <- Hint.interpret ("Hyper.displayIO " ++ Hint.parens expr) (as :: IO Graphic)
-    liftIO $ do
-        g <- m
-        evaluate (force g)      -- See NOTE [EvaluateToNF]
+-- | Evalute an input cell.
+eval         hint input = run hint $ do
+    mgs <- forM (parseStmts input) $ \line -> case line of
+        Expr expr -> do
+            -- NOTE: We wrap results into an implicit call to Hyper.display
+            m <- Hint.interpret ("Hyper.displayIO " ++ Hint.parens expr) (as :: IO Graphic)
+            liftIO $ do
+                g <- m
+                x <- evaluate (force g)      -- See NOTE [EvaluateToNF]
+                return $ Just x
+        Bind var stmt -> do
+            Hint.runStmt (var ++ "<- " ++ Hint.parens stmt)
+            return Nothing
+    return . combineGraphics $ catMaybes mgs
+
+combineGraphics :: [Graphic] -> Graphic
+combineGraphics xs = Graphic { gHtml = T.concat $ map gHtml xs }
+
+-- | Statements that we can evaluate.
+type Var  = String
+data Stmt = Expr String | Bind Var String
+
+-- | Parse an input cell into a list of statements to evaluate.
+parseStmts :: String -> [Stmt]
+parseStmts = map parseStmt . map unlines . groupByIndent . stripIndent . lines
+    where
+    indent xs      = if null xs then 0 else length . takeWhile (== ' ') $ head xs 
+    stripIndent xs = map (drop $ indent xs) xs
+    groupByIndent  = groupBy (\x y -> indent [y] > 0)
+
+parseStmt xs = case words xs of
+    (name:"<-":stmt) -> Bind name $ unwords stmt
+    _                -> Expr xs
+
 
 {- NOTE [EvaluateToNF]
 

haskell/hyper-haskell-server/hyper-haskell-server.cabal

@@ -1,5 +1,5 @@
 Name:               hyper-haskell-server
-Version:            0.1.0.2
+Version:            0.2.0.0
 Synopsis:           Server back-end for the HyperHaskell graphical Haskell interpreter
 Description:
   This package is part of the /HyperHaskell/ project and provides
@@ -26,7 +26,7 @@ Executable hyper-haskell-server
                         , bytestring   >= 0.9   && < 0.11
                         , deepseq      >= 1.2   && < 1.5
                         , exceptions   >= 0.6   && < 0.9
-                        , hint         >= 0.4   && < 0.8
+                        , hint         >= 0.7   && < 0.8
                         , hyper        == 0.1.*
                         , text         >= 0.11  && < 1.3
                         , transformers >= 0.3   && < 0.6

haskell/stack.yaml

@@ -1,6 +1,7 @@
 resolver: lts-5.8
 extra-deps:
-  - hint-0.6.0
+#  we need a custom version of hint
+#  - hint-0.6.0
 # diagrams and SVG
   - diagrams-core-1.3.0.8
   - diagrams-lib-1.3.1.3
@@ -20,5 +21,9 @@ packages:
   - hyper
   - hyper-extra
   - hyper-haskell-server
+  - location:
+      git: https://github.com/mvdan/hint
+      commit: f10e357d8249bc4b8a71e2c211bebc202549c765
+    extra-dep: true
 #  - location: lib/hint-0.4.2.3-patched
 #    extra-dep: true

worksheets/Prelude.hhs

@@ -16,6 +16,26 @@
     {
       "cell_type": "code",
       "source": "let fibs = 1 : 1 : zipWith (+) fibs (tail fibs) in take 20 fibs :: [Int]"
+    },
+    {
+      "cell_type": "text",
+      "source": "It is also possible to bind new variables in the IO monad, via a statement.\n"
+    },
+    {
+      "cell_type": "code",
+      "source": "test <- return \"Hello\""
+    },
+    {
+      "cell_type": "code",
+      "source": "test"
+    },
+    {
+      "cell_type": "text",
+      "source": "Input cells can span multiple lines. Statements are executed in sequence.\n"
+    },
+    {
+      "cell_type": "code",
+      "source": "test <- return \"Multiple lines\"\ntest"
     }
   ],
   "importModules": "Prelude",