# Authoring Parson's problem blocks

Parson’s problems require students to assemble pre-written text into a correct order by dragging blocks into a tree structure. This block is needed to hold the javascript and strings which students can drag.

STACK provides a [[parsons]] ... [[/ parsons]] question block. The question author pre-defines strings to drag within the block. These strings can be defined as Maxima variables in the question text, or just defined within the question block itself.

Users interact with the strings, dragging them into a tree structure. Note, a list is a special case of a more structured tree. The block can be linked to a STACK input so that the student's configuration can be stored and/or assessed. This page is reference documentation for the [[parsons]] block. Documentation on how to use this block in a complete question is given under topics: Authoring Parson's problems.

## Authoring JSON within the question text itself.

Here is a basic example of use:

[[parsons input="ans1"]]
{
"1":"Assume that \$$n\$$ is odd.",
"2":"Then there exists an \$$m\\in\\mathbb{Z}\$$ such that \$$n=2m+1\$$.",
"3":"\$n^2 = (2m+1)^2 = 2(2m^2+2m)+1.\$",
"4":"Define \$$M=2m^2+2m\\in\\mathbb{Z}\$$ then \$$n^2=2M+1\$$.",
}
[[/parsons]]


Assume the question author writes a list proof_steps of pairs ["key", "string"] in Maxima (as in the examples), in the question variables with both the correct and incorrect strings.

[[parsons input="ans1" ]]
{# stackjson_stringify(proof_steps) #}
[[/parsons]]


or they can avoid strings going via Maxima at all by writing JSON directly

Both these approaches can be combined, assuming proof_steps is a list of pairs ["key", "string"] as in previous examples.

[[parsons input="ans1"]]
{
"1":{#proof_steps[1][2]#},
"2":"Then there exists an \$$m\\in\\mathbb{Z}\$$ such that \$$n=2m+1\$$.",
"3":"\$n^2 = (2m+1)^2 = 2(2m^2+2m)+1.\$",
"4":"Define \$$M=2m^2+2m\\in\\mathbb{Z}\$$ then \$$n^2=2M+1\$$.",
}
[[/parsons]]


Note the \ character needs to be protected within strings, so for example we have to type \$$n=2m+1\$$ rather than just $$n=2m+1$$.

## Customising the [[parsons]] block

### JSON "options"

The [[parsons]] block is a wrapper for the javascript library "Sortable.js", optimised and with default options for Parson's problems. Moreover, there are default settings we add in, such as the headers for each of the two lists. These may be customised by structuring the JSON in the block contents as follows:

[[parsons input="ans1"]]
{ "steps": {# stackjson_stringify(proof_steps) #},
"options": {"sortable option 1" : value, ..., "sortable option n" : value},
}
[[/parsons]]


A list of all Sortable.js options can be found here, currently these are set at the default option for "animation" which controls the animation speed.

{
"animation": 50,
}


Most other Sortable options can be modified, except for ghostClass, group and onSort as these are required to be set for basic functionality.

Note that if you enter an unknown sortable option or if an attempt to pass ghostClass, group, or onSort is made, then these will simply be ignored. A warning will be displayed on the question page to signify this situation.

{
}


#### Troubleshooting

If your Parson's problem is not displaying properly, in particular if the all the items are displayed in a single yellow block, then double-check that you have spelled the keys of the JSON inside the Parsons block correctly as described above. They should be a subset of

{"steps", "options", "headers", "available_header"}


and a superset of

{"steps"}


For technical reasons this is one error that we are unable to validate currently.

### Block parameters

Functionality and styling can be customised through the use of block parameters.

1. input: string. The name of the STACK input variable (e.g., "ans1"), this links to an internal state parameter that updates the input as a Maxima expression so that it can be stored and evaluated by a PRT.
2. height: string containing a positive float + a valid CSS unit (e.g."480px", "100%", ...). Default is to create a window of automatic height to fit all the content upon load. Entering a value for the height parameter in the block header fixes the height of the window containing the drag-and-drop lists and will disable automatic resizing of the window containing the lists. Students will still be able to automatically resize the window with the expand button.
3. width: string containing a positive float + a valid CSS unit (e.g."480px", "100%", ...). Default is "100%". This fixes the width of the window containing the drag-and-drop lists.
4. aspect-ratio: string, containing a float between 0 and 1. This can be used with height/length or width (not both) and automatically determines the value of the un-used parameter in accordance with the value of aspect-ratio; unset by default. An error will occur if one sets values for aspect-ratio, width, height or aspect-ratio, width, length.
5. clone: string of the form "true" or "false". It is "false" by default. When "false" there are two lists and each proof step is "single-use", here the author must write all necessary proof steps even if they repeat; when "true" all proof steps are re-usable with no restrictions on how many times they are used, steps can only be dragged from the available list into the answer list, and there is a bin to tidy up steps.
6. override-css: string containing the location of a local CSS file contained in question/type/stack/corsscripts/ directory in the format cors://file-name or a href to an external CSS stylesheet. This will override all CSS styling of the drag-and-drop listing, so it should be used with care. However, it can be used to customise the styling of the lists by writing one's own custom CSS file and passing in the location of that file to this parameter. This parameter is unset by default.
7. override-js: string containing a local JavaScript library or a href to a cdn of a JavaScript library. This will overwrite the Sortable library used with the library identified by the string. This should be used if one wishes to use an updated version of the Sortable library, or adding functionality with a custom library. Note that the custom library will need to either extend or import the base Sortable functionality. Unset by default.
8. version: string of the form "local" or "cdn". Whether to use STACK's local copy of the Sortable library or whether to pull version 1.15.0 of Sortable from cdn. This is "local" by default.
9. columns : string containing an integer "n". How many vertical answer lists to display. By default, this is not used. If it is specified, then the styling will change to a grid-format with multiple vertical answer lists of unspecified length.
10. rows : string containing an integer "m". How many horizontal answer lists to display. By default, this is not used. If it is specified and columns is not specified, this will change to a grid-format with multiple horizontal answer lists of unspecified width. If both columns and rows are specified then this will provide a fixed length and width grid format, where items can be dragged to any position in the grid in any order. You cannot specify rows without specifying columns.
11. transpose : "true" or "false"; "false" by default. While the student is able to re-orient between vertical and horizontal as they wish, the default on load is for columns to be vertical. If you wish them to default to being horizontal, then pass transpose="true".

## Random generation of proof_step order

To track which random variants of a question a student sees, and make sure they return to the same variant, we need to perform all randomisation at the Maxima level.

To create a random order, you must define steps as Maxima objects using a proof_steps list (see the documentation of for CAS libraries for representing text-based proofs) then you can randomly order the proof_steps as follows.

1. Define a variable proof_steps as normal.
2. Add in proof_steps:random_permutation(proof_steps); to the question variables.
3. Add in a question note such as {@map(first, proof_steps)@} to create a meaningful, minimal, question note giving the order of steps.

### Randomisation bug report and workaround, 2nd August 2024

If using numerical keys (in the format of an actual number 1 or as a string "1") then as of the time of writing this will not be randomised correctly and will appear on the question page in the order of the numerical tags. To resolve this use any other keys, either descriptive strings or "step_1" if enumeration is required or preferred.

This will be fixed in a future version, Issue #1237.

## Block connection with Maxima

All communication to and from the Parsons block uses the JSON format. However, internally STACK uses maxima objets. We therefore need to convert between Maxima syntax and JSON format.

1. The maxima function stackjson_stringify(proof_steps) will convert a list of proof_steps into a JSON string.
2. The maxima function proof_parsons_interpret(ans1) will convert a JSON string into a proof construction function.
3. The maxima function proof_parsons_key_json(ta, proof_steps) takes the teacher's answer ta and a list of proof steps proof_steps and creates a JSON string which represents ta and lists any available (unused) strings from the proof_steps list. This function is needed to set up the "model answer" field in the inputs from a maxima representation of the proof.

### Block parameters: height and width

Additional display options including height and width may also be passed to the header, as in

[[parsons input="ans1" height="360px" width="100%"]]
{
"1":"Assume that \$$n\$$ is odd.",
"2":"Then there exists an \$$m\\in\\mathbb{Z}\$$ such that \$$n=2m+1\$$.",
"3":"\$n^2 = (2m+1)^2 = 2(2m^2+2m)+1.\$",
"4":"Define \$$M=2m^2+2m\\in\\mathbb{Z}\$$ then \$$n^2=2M+1\$$.",
"5":"Assume that \$$n\$$ is even.",
"6":"Then there exists an \$$m\\in\\mathbb{Z}\$$ such that \$$n = 2m\$$."
};
[[/parsons]]


## Adding plots to a Parson's block

Since HTML can be embedded into strings dragged within a Parson's block, images can be included with the HTML <img> tags as normal.

STACK-generated plots can also be included just using {@plot(x^2,[x,-1,1])@} as might be expected. This is because of the order of evaluation. The full URL of the image is only created in the (complex) chain of events after the value has been substituted into the javascript code.

[[parsons input="ans1"]]
{
"A":"The inverse function of \$$f(x)=x^2\$$ has graph",
"B":{#plot(x^2,[x,-1,1],[size,250,250])#},
};
[[/parsons]]


Notice that since the value of plot(...) is a Maxima string of <img> tag, there is no need to add in string quotes when defining the JSON above. The {#...#} will print " as part of the output. However, for convenience string quotes are removed from the display form {@...@} (as typically you just want the plot without quotes). Hence this is an alternative.

[[parsons input="ans1"]]
{
"A":"The inverse function of \$$f(x)=x^2\$$ has graph",
"B":"{@plot(sqrt(x),[x,-1,1],[size,250,250])@}",
};
[[/parsons]]


An alternative is to use the Maxima castext function, e.g.

s1:castext("Consider this graph {@plot(x^2,[x,-1,1],[size,250,250])@}");


and then use the value of s1, in the Parson's block within the question text

[[parsons input="ans1"]]
{
"A":"The inverse function of \$$f(x)=x^2\$$ has graph",
"B":"{@s1@}",
};
[[/parsons]]


A last direct example of question variables

proof_steps:[
[ "A", plot(sqrt(x),[x,-1,1],[size,180,180],[margin,1.7],[yx_ratio, 1],[plottags,false])],
[ "B", plot(x,[x,-1,1],[size,180,180],[margin,1.7],[yx_ratio, 1],[plottags,false])],
[ "C", plot(x^2,[x,-1,1],[size,180,180],[margin,1.7],[yx_ratio, 1],[plottags,false])],
[ "D", plot(x^3,[x,-1,1],[size,180,180],[margin,1.7],[yx_ratio, 1],[plottags,false])]
];


## Adding trees to a Parson's block

STACK enables question authors to display the tree structure of an algebraic expression using castext {@disptree(1+2+pi*x^3)@}.