add functions to the language

docs/faq.md

@@ -242,7 +242,7 @@ Similar logic applies for situations when you only specify the `mode` parameter.
 This all turns out to be more safe and "correct", in that it would error and
 prevent masking an error for a situation when you expected a file to already be
 at that location. It also turns out to simplify the internals significantly, and
-remove an ambiguous scenario with the reversable file resource.
+remove an ambiguous scenario with the reversible file resource.
 
 ### Why do function names inside of templates include underscores?
 

docs/language-guide.md

@@ -563,21 +563,20 @@ would like to propose a more logical or performant variant.
 
 #### Function graph generation
 
-At this point we have a fully type AST. The AST must now be transformed into a
+At this point we have a fully typed AST. The AST must now be transformed into a
 directed, acyclic graph (DAG) data structure that represents the flow of data as
 necessary for everything to be reactive. Note that this graph is *different*
 from the resource graph which is produced and sent to the engine. It is just a
-coincidence that both happen to be DAG's. (You don't freak out when you see a
+coincidence that both happen to be DAG's. (You aren't surprised when you see a
 list data structure show up in more than one place, do you?)
 
 To produce this graph, each node has a `Graph` method which it can call. This
 starts at the top most node, and is called down through the AST. The edges in
 the graphs must represent the individual expression values which are passed
 from node to node. The names of the edges must match the function type argument
 names which are used in the definition of the corresponding function. These
-corresponding functions must exist for each expression node and are produced by
-calling that expression's `Func` method. These are usually called by the
-function engine during function creation and validation.
+corresponding functions must exist for each expression node and are produced as
+the vertices of this returned graph. This is built for the function engine.
 
 #### Function engine creation and validation
 

examples/lang/map-iterator0.mcl

@@ -0,0 +1,13 @@
+import "iter"
+
+$fn = func($x) { # notable because concrete type is fn(t1) t2, where t1 != t2
+	len($x)
+}
+
+$in1 = ["a", "bb", "ccc", "dddd", "eeeee",]
+
+$out1 = iter.map($in1, $fn)
+
+$t1 = template("out1: {{ . }}", $out1)
+
+test $t1 {}

examples/lang/map-iterator1.mcl

@@ -0,0 +1,28 @@
+import "datetime"
+import "iter"
+import "math"
+
+$now = datetime.now()
+
+# alternate every four seconds
+$mod0 = math.mod($now, 8) == 0
+$mod1 = math.mod($now, 8) == 1
+$mod2 = math.mod($now, 8) == 2
+$mod3 = math.mod($now, 8) == 3
+$mod = $mod0 || $mod1 || $mod2 || $mod3
+
+$fn = func($x) { # notable because concrete type is fn(t1) t2, where t1 != t2
+	len($x)
+}
+
+$in1 = if $mod {
+	["a", "bb", "ccc", "dddd", "eeeee",]
+} else {
+	["ffffff", "ggggggg", "hhhhhhhh", "iiiiiiiii", "jjjjjjjjjj",]
+}
+
+$out1 = iter.map($in1, $fn)
+
+$t1 = template("out1: {{ . }}", $out1)
+
+test $t1 {}

gapi/gapi.go

@@ -119,11 +119,13 @@ type GAPI interface {
 
 	// Next returns a stream of switch events. The engine will run Graph()
 	// to build a new graph after every Next event.
+	// TODO: add context for shutting down to the input and change Close to Cleanup
 	Next() chan Next
 
 	// Close shuts down the GAPI. It asks the GAPI to close, and must cause
 	// Next() to unblock even if is currently blocked and waiting to send a
 	// new event.
+	// TODO: change Close to Cleanup
 	Close() error
 }