From 4c6c1bcf877017df98d4a5492a665eca12b8ba98 Mon Sep 17 00:00:00 2001
From: Lars-Dominik Braun <lars@6xq.net>
Date: Sun, 28 Jun 2015 16:42:19 +0200
Subject: Replace file magic with directives

Adds the %pesto and %bonappetit directives, switches to stream-based
operation.
---
 src/Codec/Pesto/Graph.lhs | 65 +++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 57 insertions(+), 8 deletions(-)

(limited to 'src/Codec/Pesto/Graph.lhs')

diff --git a/src/Codec/Pesto/Graph.lhs b/src/Codec/Pesto/Graph.lhs
index 4ea2886..7376c5f 100644
--- a/src/Codec/Pesto/Graph.lhs
+++ b/src/Codec/Pesto/Graph.lhs
@@ -11,18 +11,56 @@ Language semantics
 > 	, firstNodeId
 > 	, resolveReferences
 > 	, test
+> 	, extract
 > 	) where
 > import Data.Char (isSpace, toLower, isLetter)
 > import Data.List (sort, nub)
 > import Test.HUnit hiding (test)
+> import Control.Applicative ((<$>))
 >
 > import Codec.Pesto.Parse hiding (test)
 
-Pesto’s syntax drives a stack-based machine that transforms the linear stream
-of operations generated by the parser into a directed graph. Think of the stack
-as your kitchen’s workspace that is used to prepare the food’s
-components. You can add new ingredients, perform actions on them, put them
-aside and add them again.
+The parser’s output, a stream of operations, may contain multiple recipes. A
+recipe must start with the directive “pesto” and may end with “bonappetit”.
+This function extracts all recipes from the stream and removes both directives.
+
+- easily embed recipes into other documents
+
+> extract [] = []
+> extract (Directive "pesto":stream) = between:extract next
+> 	where
+> 		isEnd (Directive x) | x `elem` ["bonappetit", "pesto"] = True
+> 		isEnd _ = False
+> 		(between, next) = break isEnd stream
+> extract (x:xs) = extract xs
+
+Start and end directive are removed from the extracted operations.  The
+directive “bonappetit” is optional at the end of a stream.
+
+> testExtract = [
+> 	  extract [Directive "pesto", Directive "bonappetit"] ~?= [[]]
+> 	, extract [Directive "pesto", Action "foobar", Directive "bonappetit"] ~?= [[Action "foobar"]]
+> 	, extract [Directive "pesto"] ~?= [[]]
+> 	, extract [Directive "pesto", Directive "foobar"] ~?= [[Directive "foobar"]]
+
+Operations surrounding the start and end directive are removed.
+
+> 	, extract [Unknown "Something", Directive "pesto"] ~?= [[]]
+> 	, extract [Unknown "Something", Action "pour", Directive "pesto"] ~?= [[]]
+> 	, extract [Directive "pesto", Directive "bonappetit", Annotation "something"] ~?= [[]]
+
+The stream may contain multiple recipes. The start directive also ends the
+previous recipe and starts a new one.
+
+> 	, extract [Directive "pesto", Action "pour", Directive "bonappetit", Action "foobar", Directive "pesto", Annotation "something"] ~?= [[Action "pour"], [Annotation "something"]]
+> 	, extract [Directive "pesto", Action "heat", Directive "pesto", Annotation "something"] ~?= [[Action "heat"], [Annotation "something"]]
+> 	, extract [Directive "pesto", Annotation "foobar", Directive "pesto", Directive "bonappetit"] ~?= [[Annotation "foobar"], []]
+> 	]
+
+Each recipe’s stream of operations drives a stack-based machine that transforms
+it into a directed graph. Think of the stack as your kitchen’s workspace that
+is used to prepare the food’s components. You can add new ingredients, perform
+actions on them, put them aside and add them again.
 
 This function processes a list of nodes, that is operations uniquely identified
 by an integer and returns the edges of the directed graph as a list of tuples.
@@ -74,6 +112,12 @@ used to provide more information about ingredients (so “hot water” becomes
 > 		f ctx@(Nothing, s, edges) (_, Annotation _) = ctx
 > 		f (Just prev, s, edges) (i, Annotation _) = (Just prev, s, (i, prev):edges)
 
+Unused directives or unknown operations are danging nodes with no connection to
+other nodes.
+
+> 		f ctx (_, Directive _) = ctx
+> 		f ctx (_, Unknown _) = ctx
+
 These are helper functions:
 
 > 		addToStack (_, stack:sx, edges) i = (Just i, (i:stack):sx, edges)
@@ -126,6 +170,11 @@ to the same node.
 > 	, cmpGraph "+foobar >barbaz (C)" [(0, 1), (2, 1)]
 > 	, cmpGraph "+foobar |barbaz (C)" [(0, 1), (2, 1)]
 > 	, cmpGraph "*foobar (C)" [(1, 0)]
+
+Unknown directives or operations are never connected to other nodes.
+
+> 	, cmpGraph "%invalid" []
+> 	, cmpGraph "invalid" []
 > 	]
 
 References
@@ -183,8 +232,8 @@ Appendix
 
 > runGraphWith f doc expect = sort edges ~?= sort expect
 > 	where
-> 		(Right op) = parse ("%pesto-1 " ++ doc)
-> 		nodes = (zip [firstNodeId..] . map snd . operations) op
+> 		(Right op) = (head . extract . snd . unzip) <$> parse ("%pesto " ++ doc)
+> 		nodes = zip [firstNodeId..] op
 > 		edges = f nodes
 > cmpGraph = runGraphWith toGraph
 > cmpGraphRef = runGraphWith resolveReferences
@@ -202,5 +251,5 @@ Get all nodes with edges pointing towards nodeid
 
 > outgoing edges (nodeid, _) = filter ((==) nodeid . fst) edges
 
-> test = ["graph" ~: testGraph, "ref" ~: testRef]
+> test = ["graph" ~: testGraph, "ref" ~: testRef, "extract" ~: testExtract]
 
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