Sollya User's Manual

Name:

isbound indicates whether a variable is bound or not.

Usage:

isbound(ident) : boolean

Parameters:

ident is a name.

Description:

isbound(ident) returns a boolean value indicating whether the name ident is used or not to represent a variable. It returns true when ident is the name used to represent the global variable or if the name is currently used to refer to a (possibly local) variable.
When a variable is defined in a block and has not been defined outside, isbound returns true when called inside the block, and false outside. Note that isbound returns true as soon as a variable has been declared with var, even if no value is actually stored in it.
If ident1 is bound to a variable and if ident2 refers to the global variable, the command rename(ident2, ident1) hides the value of ident1 which becomes the global variable. However, if the global variable is again renamed, ident1 gets its value back. In this case, isbound(ident1) returns true. If ident1 was not bound before, isbound(ident1) returns false after that ident1 has been renamed.

Example 1:

   > isbound(x);
   false
   > isbound(f);
   false
   > isbound(g);
   false
   > f=sin(x);
   > isbound(x);
   true
   > isbound(f);
   true
   > isbound(g);
   false

Example 2:

   > isbound(a);
   false
   > { var a; isbound(a); };
   true
   > isbound(a);
   false

Example 3:

   > f=sin(x);
   > isbound(x);
   true
   > rename(x,y);
   > isbound(x);
   false

Example 4:

   > x=1;
   > f=sin(y);
   > rename(y,x);
   > f;
   sin(x)
   > x;
   x
   > isbound(x);
   true
   > rename(x,y);
   > isbound(x);
   true
   > x;
   1

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