Re: Help- error in executing "retract" predicate

[Nico Di Mauro]

Hello Vidhya,

Wednesday, February 27, 2002, 1:52:24 PM, you wrote:

VS> Respected sir/madam,
VS>        i am using "SWI-Prolog" to find a solution for
VS> timetabling problem. here is a small piece of code

VS> ================ code ============================

VS> sam(1).
VS> soln:-sam(X),retract(sam(X)),write(success).

VS> ==================================================

VS>         this code on execution gives the following
VS> error

VS> ================= error ===========================

VS> [succ].
VS> % succ compiled 0.00 sec, 0 bytes

VS> Yes

VS> ?- soln.
VS> ERROR: No permission to modify static_procedure
VS> `sam/1'
VS> ^  Exception: (7) retract(sam(1)) ? retry
VS> [retry]
VS> ^  Call: (7) retract(sam(1)) ? creep
VS> ERROR: No permission to modify static_procedure
VS> `sam/1'
VS> ^  Exception: (7) retract(sam(1)) ? creep

VS> ======================================================

VS>       i want to use "assert" and "retract" to add
VS> facts and delete facts from the database.
VS>       can anyone help me to find the error in my
VS> program and to execute these 2 commands

VS>                 thanking you,

VS> yours faithfully,
VS> vidhya

You must declare the predicate sam as dynamic.

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