CAS command question

[Han]

(01-06-2017 06:59 PM)compsystems Wrote:  Now step by step

expr( "'"+s+"'" ); ⇨ (1/3)*x+(1/6)*y ≤ 80 ⇦ It has removed the quotes (Apparently well.). The quotation marks must be preserved
the next step fails Copying to the entry line
[up] [copy] [enter] 80≥ (1/3)*x+(1/6)*y (wrong for the above reason)

expr( "'"+s+"'" ); ⇨ '(1/3)*x+(1/6)*y ≤ 80' // This is the correct output

An easier example
HP-PRIME
3+4; [ENTER] 7 // ok
'3+4'; [ENTER] 3+4 (Apparently well.).
[up key] [copy] 3+4 [enter] 7 // wrong

This should be copied with quotation marks, or better with the function QUOTE()
[up key] [copy] '3+4' or quote(3+4) [enter] '3+4' // ok

HP50G
'3+4' [ENTER] '3+4' // ok
[up or HIST key] [copy (right-shift+var)] then [on] [paste] [ENTER] '3+4' // ok and not 7

You keep forgetting that the parser, like with almost any other CAS software, will generally evaluate its input. Evaluation of a quoted expression results in an unquoted expression. The net effect is essentially stripping the quotation. So copying the result would be copying an unquoted expression, which is why [up key][copy] gives you 3+4 on the command line, and not '3+4'. Try [up key] twice before copying.

On the HP50G, evaluation of a symbolic object merely copies the object onto the stack because an expression and a 'quoted expression' are one and the same. They (Prime vs HP50G) also have different evaluation schemes due to their different object representations.