String-handling functions

 

Detecting null strings

 

Usage

• empty$  operator; one argument in parenthesis. is the name of a string.

This is a boolean operator which returns the value unity if is an empty string (or if is not a string), and zero if it is a string with positive length.  

Comparing strings for equality

 
Usage

• eq$  operator; two arguments and in parenthesis and separated by a comma. and are the names of strings or sequences of alphanumeric characters.

By default, S1 and S2 are assumed to be the names of defined strings. If either string is not recognised, then the name supplied given is used instead. This is a boolean operator which returns the value unity if the string\ is equal to the string , and zero otherwise. The complementary operator is neq$ . For example, suppose that we have defined only the strings a=mustard and b=cress. Then:

• is equal to zero, as the strings `mustard' and `cress' are not equal;
• is equal to one, as a is taken to be the string `mustard' and `mustard' is not a string, and therefore taken to mean itself.

 

String length

 
Usage

• len$  operator; one argument in parenthesis. is the name of a string or a sequence of alphanumeric characters.

This returns the length of the string as a non-negative integer. If the string has not been defined, then the length of the alphanumeric sequence supplied as the name of the string is returned.

If the string has been defined, but is empty, the length is defined to be zero.  

Comparing strings for inequality

 
Usage

• neq$  operator; two arguments and in parenthesis and separated by a comma. and are the names of strings or sequences of alphanumeric characters.

By default, S1 and S2 are assumed to be the names of defined strings. If either string is not recognised, then the name supplied given is used instead. This is a boolean operator which returns the value zero if the string\ is equal to the string , and unity otherwise. The complementary operator is eq$ . For example, suppose that we have defined only the strings a=mustard and b=cress. Then:

• is equal to one, as the strings `mustard' and `cress' are not equal;
• is equal to zero, as a is taken to be the string `mustard' and `mustard' is not a string, and therefore taken to mean itself. Consequently these two are equal, and the operator returns a value indicating false.

 

Detecting numeric strings

 
Usage

• real$  operator; one argument in parenthesis. is the name of a string or a sequence of alphanumeric characters.

If the name S supplied has not been defined as a string, then the name itself is used as the string. This is an operator which returns the integer value zero, one or two depending upon the form of the string\ :

1

is returned if is of the form d.d, optionally preceded by a minus sign;

2

is returned if is of the form d, optionally preceded by a minus sign;

0

is returned if neither of the above applies.

where d represents at least one digit. Note in particular that the decimal point must be both preceded and succeeded by at least one digit if this operator is to return a value of unity. For example, and .