Add Streams library (#381)

* Add stream library and test

* Remove streams test

Integrating another test tool into this will take a non-trivial amount
of time, and can be done together with tests for the other libraries.

* Add stream_max

Also just copied the grader file for solidarity

* Add file when loading website

* Add streams library name

* Add functions for streams

* Remove stream_take_max

* Remove stream_take_max from externalLibraries

* Bump version

package.json

@@ -1,7 +1,7 @@
 {
   "private": true,
   "name": "cadet-frontend",
-  "version": "1.0.13",
+  "version": "1.0.14",
   "scripts-info": {
     "format": "Format source code",
     "start": "Start the Webpack development server",

public/externalLibs/index.js

@@ -34,6 +34,8 @@ function loadAllLibs() {
     '/externalLibs/visualizer/visualizer.js',
     // binary tree library
     '/externalLibs/tree.js',
+    // streams
+    '/externalLibs/streams/stream.js',
   ];
 
   for (var i = 0; i < files.length; i++) {

public/externalLibs/streams/stream.js

@@ -0,0 +1,308 @@
+// stream.js: Supporting streams in the Scheme style, following
+//            "stream discipline"
+// A stream is either the empty list or a pair whose tail is
+// a nullary function that returns a stream.
+
+// Author: Martin Henz
+
+// stream_tail returns the second component of the given pair
+// throws an exception if the argument is not a pair
+// LOW-LEVEL FUNCTION, NOT JEDISCRIPT
+function stream_tail(xs) {
+    var tail;
+    if (is_pair(xs)) {
+        tail = xs[1];
+    } else {
+        throw new Error("stream_tail(xs) expects a pair as "
+            + "argument xs, but encountered " + xs);
+    }
+
+    if (typeof tail === "function") {
+        return tail();
+    } else {
+        throw new Error("stream_tail(xs) expects a function as "
+            + "the tail of the argument pair xs, "
+            + "but encountered " + tail);
+    }
+}
+
+// is_stream recurses down the stream and checks that it ends with
+// the empty list []; does not throw any exceptions
+// LOW-LEVEL FUNCTION, NOT JEDISCRIPT
+// Lazy? No: is_stream needs to go down the stream
+function is_stream(xs) {
+    return (array_test(xs) && xs.length === 0)
+    || (is_pair(xs) && typeof tail(xs) === "function" &&
+            is_stream(stream_tail(xs)));
+}
+
+// list_to_stream transforms a given list to a stream
+// Lazy? Yes: list_to_stream goes down the list only when forced
+function list_to_stream(xs) {
+    if (is_empty_list(xs)) {
+        return [];
+    } else {
+        return pair(head(xs),
+                    function() {
+                        return list_to_stream(tail(xs));
+                    });
+    }
+}
+
+// stream_to_list transforms a given stream to a list
+// Lazy? No: stream_to_list needs to force the whole stream
+function stream_to_list(xs) {
+    if (is_empty_list(xs)) {
+        return [];
+    } else {
+        return pair(head(xs), stream_to_list(stream_tail(xs)));
+    }
+}
+
+// stream makes a stream out of its arguments
+// LOW-LEVEL FUNCTION, NOT JEDISCRIPT
+// Lazy? No: In this implementation, we generate first a
+//           complete list, and then a stream using list_to_stream
+function stream() {
+    var the_list = [];
+    for (var i = arguments.length - 1; i >= 0; i--) {
+        the_list = pair(arguments[i], the_list);
+    }
+    return list_to_stream(the_list);
+}
+
+// stream_length returns the length of a given argument stream
+// throws an exception if the argument is not a stream
+// Lazy? No: The function needs to explore the whole stream
+function stream_length(xs) {
+    if (is_empty_list(xs)) {
+        return 0;
+    } else {
+        return 1 + stream_length(stream_tail(xs));
+    }
+}
+
+// stream_map applies first arg f to the elements of the second
+// argument, assumed to be a stream.
+// f is applied element-by-element:
+// stream_map(f,list_to_stream([1,[2,[]]])) results in
+// the same as list_to_stream([f(1),[f(2),[]]])
+// stream_map throws an exception if the second argument is not a
+// stream, and if the second argument is a non-empty stream and the
+// first argument is not a function.
+// Lazy? Yes: The argument stream is only explored as forced by
+//            the result stream.
+function stream_map(f, s) {
+    if (is_empty_list(s)) {
+       return [];
+    } else {
+        return pair(f(head(s)),
+                    function() {
+                        return stream_map(f, stream_tail(s));
+                    });
+    }
+}
+
+// build_stream takes a non-negative integer n as first argument,
+// and a function fun as second argument.
+// build_list returns a stream of n elements, that results from
+// applying fun to the numbers from 0 to n-1.
+// Lazy? Yes: The result stream forces the applications of fun
+//            for the next element
+function build_stream(n, fun) {
+    function build(i) {
+        if (i >= n) {
+            return [];
+        } else {
+            return pair(fun(i),
+                        function() {
+                            return build(i + 1);
+                        });
+        }
+    }
+    return build(0);
+}
+
+// stream_for_each applies first arg fun to the elements of the list
+// passed as second argument. fun is applied element-by-element:
+// for_each(fun,list_to_stream([1,[2,[]]])) results in the calls fun(1)
+// and fun(2).
+// stream_for_each returns true.
+// stream_for_each throws an exception if the second argument is not a list,
+// and if the second argument is a non-empty list and the
+// first argument is not a function.
+// Lazy? No: stream_for_each forces the exploration of the entire stream
+function stream_for_each(fun, xs) {
+    if (is_empty_list(xs)) {
+        return true;
+    } else {
+        fun(head(xs));
+        return stream_for_each(fun, stream_tail(xs));
+    }
+}
+
+// stream_reverse reverses the argument stream
+// stream_reverse throws an exception if the argument is not a stream.
+// Lazy? No: stream_reverse forces the exploration of the entire stream
+function stream_reverse(xs) {
+    function rev(original, reversed) {
+        if (is_empty_list(original)) {
+            return reversed;
+        } else {
+            return rev(stream_tail(original),
+                       pair(head(original), function() { return reversed; }));
+        }
+    }
+    return rev(xs,[]);
+}
+
+// stream_to_vector returns vector that contains the elements of the argument
+// stream in the given order.
+// stream_to_vector throws an exception if the argument is not a stream
+// LOW-LEVEL FUNCTION, NOT JEDISCRIPT
+// Lazy? No: stream_to_vector forces the exploration of the entire stream
+function stream_to_vector(lst){
+    var vector = [];
+    while (!is_empty_list(lst)) {
+        vector.push(head(lst));
+        lst = stream_tail(lst);
+    }
+    return vector;
+}
+
+// stream_append appends first argument stream and second argument stream.
+// In the result, the [] at the end of the first argument stream
+// is replaced by the second argument stream
+// stream_append throws an exception if the first argument is not a
+// stream.
+// Lazy? Yes: the result stream forces the actual append operation
+function stream_append(xs, ys) {
+    if (is_empty_list(xs)) {
+        return ys;
+    } else {
+        return pair(head(xs),
+                    function() {
+                        return stream_append(stream_tail(xs), ys);
+                    });
+    }
+}
+
+// stream_member looks for a given first-argument element in a given
+// second argument stream. It returns the first postfix substream
+// that starts with the given element. It returns [] if the
+// element does not occur in the stream
+// Lazy? Sort-of: stream_member forces the stream only until the element is found.
+function stream_member(x, s) {
+    if (is_empty_list(s)) {
+        return [];
+    } else if (head(s) === x) {
+        return s;
+    } else {
+        return stream_member(x, stream_tail(s));
+    }
+}
+
+// stream_remove removes the first occurrence of a given first-argument element
+// in a given second-argument list. Returns the original list
+// if there is no occurrence.
+// Lazy? Yes: the result stream forces the construction of each next element
+function stream_remove(v, xs) {
+    if (is_empty_list(xs)) {
+        return [];
+    } else if (v === head(xs)) {
+        return stream_tail(xs);
+    } else {
+        return pair(head(xs),
+                    function() {
+                        return stream_remove(v, stream_tail(xs));
+                    });
+    }
+}
+
+// stream_remove_all removes all instances of v instead of just the first.
+// Lazy? Yes: the result stream forces the construction of each next element
+function stream_remove_all(v, xs) {
+    if (is_empty_list(xs)) {
+        return [];
+    } else if (v === head(xs)) {
+        return stream_remove_all(v, stream_tail(xs));
+    } else {
+        return pair(head(xs), function() {
+            return stream_remove_all(v, stream_tail(xs));
+        });
+    }
+}
+
+// filter returns the substream of elements of given stream s
+// for which the given predicate function p returns true.
+// Lazy? Yes: The result stream forces the construction of
+//            each next element. Of course, the construction
+//            of the next element needs to go down the stream
+//            until an element is found for which p holds.
+function stream_filter(p, s) {
+    if (is_empty_list(s)) {
+        return [];
+    } else if (p(head(s))) {
+        return pair(head(s),
+                    function() {
+                        return stream_filter(p, stream_tail(s));
+                    });
+    } else {
+        return stream_filter(p, stream_tail(s));
+    }
+}
+
+// enumerates numbers starting from start,
+// using a step size of 1, until the number
+// exceeds end.
+// Lazy? Yes: The result stream forces the construction of
+//            each next element
+function enum_stream(start, end) {
+    if (start > end) {
+        return [];
+    } else {
+        return pair(start,
+                    function() {
+                        return enum_stream(start + 1, end);
+                    });
+    }
+}
+
+// integers_from constructs an infinite stream of integers
+// starting at a given number n
+// Lazy? Yes: The result stream forces the construction of
+//            each next element
+function integers_from(n) {
+    return pair(n,
+                function() {
+                    return integers_from(n + 1);
+                });
+}
+
+// eval_stream constructs the list of the first n elements
+// of a given stream s
+// Lazy? Sort-of: eval_stream only forces the computation of
+//                the first n elements, and leaves the rest of
+//                the stream untouched.
+function eval_stream(s, n) {
+    if (n === 0) {
+        return [];
+    } else {
+        return pair(head(s),
+                    eval_stream(stream_tail(s),
+                                n - 1));
+   }
+}
+
+// Returns the item in stream s at index n (the first item is at position 0)
+// Lazy? Sort-of: stream_ref only forces the computation of
+//                the first n elements, and leaves the rest of
+//                the stream untouched.
+function stream_ref(s, n) {
+    if (n === 0) {
+        return head(s);
+    } else {
+        return stream_ref(stream_tail(s), n - 1);
+    }
+}
+

src/components/assessment/assessmentShape.ts

@@ -93,7 +93,8 @@ export enum ExternalLibraryNames {
   TWO_DIM_RUNES = 'TWO_DIM_RUNES',
   THREE_DIM_RUNES = 'THREE_DIM_RUNES',
   CURVES = 'CURVES',
-  SOUND = 'SOUND'
+  SOUND = 'SOUND',
+  STREAMS = 'STREAMS'
 }
 
 export type ExternalLibraryName = keyof typeof ExternalLibraryNames

src/reducers/externalLibraries.ts

@@ -149,6 +149,31 @@ const libEntries: Array<[ExternalLibraryName, string[]]> = [
       'violin',
       'cello'
     ]
+  ],
+  [
+    ExternalLibraryNames.STREAMS,
+    [
+      'stream_tail',
+      'is_stream',
+      'list_to_stream',
+      'stream_to_list',
+      'stream',
+      'stream_length',
+      'stream_map',
+      'build_stream',
+      'stream_for_each',
+      'stream_reverse',
+      'stream_to_vector',
+      'stream_append',
+      'stream_member',
+      'stream_remove',
+      'stream_remove_all',
+      'stream_filter',
+      'enum_stream',
+      'integers_from',
+      'eval_stream',
+      'stream_ref'
+    ]
   ]
 ]