Error: 910 i.e. Syntax error is returned by math.evalStr() API of TI-Nspire engine

Question

Code

I have this Lua script for a TI-Nspire CAS calculator.

platform.apilevel = '2.2'

box_prompt, error = D2Editor.newRichText():resize(300, 40)
box_prompt:move(0, 0):setBorder(1):setBorderColor(0x43adee):setFontSize(12):setReadOnly(true):setSelectable(false)
    :setTextColor(0x666666):setVisible(true)
result, error = box_prompt:setText('Please enter an expression in box below')

box_expr, error = D2Editor.newRichText():resize(300, 40)
box_expr:move(0, 50):setBorder(1):setBorderColor(0x43adee):setFontSize(12):setReadOnly(false):setSelectable(true)
    :setTextColor(0x000000):setVisible(true)

box_result, error = D2Editor.newRichText():resize(300, 40)
box_result:move(0, 100):setBorder(1):setBorderColor(0x43adee):setFontSize(12):setReadOnly(false):setSelectable(true)
    :setTextColor(0x000000):setVisible(true)

box_expr_doublecheck, error = D2Editor.newRichText():resize(300, 40)
box_expr_doublecheck:move(0, 150):setBorder(1):setBorderColor(0x43adee):setFontSize(12):setReadOnly(true):setSelectable(
    false):setTextColor(0x666666):setVisible(true)

-- To evaluate the expression
function run()
    local expression = box_expr:getExpression()
    box_expr_doublecheck:setText("expression doublecheck: "..expression)
    local result, err = math.evalStr(expression)
    if err ~= nil then
        show_error(err)
        return
    end
    box_result:setText("Result: " .. result)
end

function on.escapeKey()
    run()
end

function show_error(err)
    if err == nil then
    else
        box_result:setText("Error: " .. err)
    end
end

UI

It has four rich text boxes.

The 1st box is just a read-only help.
The 2nd box is where user enters a mathematical expression.
The 3rd box will display result or error.
The 4th box will display the expression entered by the user to double-check.

Good expressions

When user enters expressions containing straightforward characters like -, +, /, *, ^ then the program works just fine:

Bad expression

However, when user employs the TI-Nspire temlates like power and division templates, then an Error: 910 is thrown which according to Error_Codes means Syntax error.

Template

By tempalte, I mean buttons like these on a TI-Nspire calculator:

Question

How can I correctly evaluate an expression that contains one or more TI-Nspire template? I played around with math.evalStr(), math.eval() and other APIs, but I couldn't figure it out. Thanks.

UPDATE: `createMathBox()`

I created a math box inside the rich text editor by this statement: box_expr:createMathBox(). Then, any text entered by the user inside that math box, even ordinaly 2+3, throws the syntax error above.

UPDATE: doc

Lua Scripting API Reference Guide provides a table with more information about annotations in proprietary markup language:

What is returned in `local expression = box_expr:getExpression()` when you entered the expression 1+3² ? — ESkri, Jun 16 '23 at 13:33
@ESkri I doublechecked the returned value of `local expression = box_expr:getExpression()` and I observe that it is: `1+3²` — Megidd, Jun 16 '23 at 13:43
So, `getExpression` returns valid html code? What is returned for other "templates"? What is returned from rich text editor? — ESkri, Jun 16 '23 at 15:01
@ESkri I believe a posted screenshot gives an example of how a *template* is returned. The returned text is dispalyed by *expression doublecheck* field on the screenshot. — Megidd, Jun 16 '23 at 15:07
Obviously, `math.evalStr` does not support the format returned by `getExpression`. You should parse it yourself or find some API function to do it for you. BTW, your links to education.ti.com website are "Access Denied" for me. — ESkri, Jun 16 '23 at 16:47

Megidd · Accepted Answer · 2023-06-16T17:56:01.267

This is the fixed code:

platform.apilevel = '2.2'

box_prompt, error = D2Editor.newRichText():resize(300, 40)
box_prompt:move(0, 0):setBorder(1):setBorderColor(0x43adee):setFontSize(12):setReadOnly(true):setSelectable(false)
    :setTextColor(0x666666):setVisible(true)
result, error = box_prompt:setText('Please enter an expression in box below')

box_expr, error = D2Editor.newRichText():resize(300, 40)
box_expr:move(0, 50):setBorder(1):setBorderColor(0x43adee):setFontSize(12):setReadOnly(false):setSelectable(true)
    :setTextColor(0x000000):setVisible(true)
matbox = box_expr:createMathBox() -- Math Box

box_result, error = D2Editor.newRichText():resize(300, 40)
box_result:move(0, 100):setBorder(1):setBorderColor(0x43adee):setFontSize(12):setReadOnly(false):setSelectable(true)
    :setTextColor(0x000000):setVisible(true)

box_expr_doublecheck, error = D2Editor.newRichText():resize(300, 40)
box_expr_doublecheck:move(0, 150):setBorder(1):setBorderColor(0x43adee):setFontSize(12):setReadOnly(true):setSelectable(
    false):setTextColor(0x666666):setVisible(true)

-- To evaluate the expression
function run()
    local markup = matbox:getExpression()
    -- Math Box markup is "\0el {...}"
    -- Get everything between the curly braces
    local E = markup:match("{(.*)}")
    box_expr_doublecheck:setText("markup:" .. markup .. "   string:" .. E)
    local result, err = math.evalStr(E)
    if err ~= nil then
        show_error(err)
        return
    end
    box_result:setText("Result: " .. result)
end

function on.escapeKey()
    run()
end

function show_error(err)
    if err == nil then
    else
        box_result:setText("Error: " .. err)
    end
end

As can be seen, the annotations in proprietary markup language should be considered:

Solution

These statements were the key:

matbox = box_expr:createMathBox() -- Math Box

-- ...

    local markup = matbox:getExpression()
    -- Math Box markup is "\0el {...}"
    -- Get everything between the curly braces
    local E = markup:match("{(.*)}")
    
    local result, err = math.evalStr(E)

-- ...

General case

This is a general function to remove all occurances of markup characters \0el { and } inside an input string:


function delete_markup(strI)
    -- Remove all occurrences of "\0el {" and "}" inside string
    local strO = strI:gsub("\\0el {(.-)}", "%1")
    return strO
end