Forth 2012: FLOAT

( c-addr u -- true | false ) ( F: -- r | ~ ) or ( c-addr u -- r true | false )

An attempt is made to convert the string specified by c-addr and u to internal floating-point representation. If the string represents a valid floating-point number in the syntax below, its value r and true are returned. If the string does not represent a valid floating-point number only false is returned.

A string of blanks should be treated as a special case representing zero.

The syntax of a convertible string

	:=	<significand>[<exponent>]
<significand>	:=	[<sign>]{<digits>[.<digits0>] \| .<digits> }
<exponent>	:=	<marker><digits0>
<marker>	:=	{<e-form> \| <sign-form>}
<e-form>	:=	<e-char>[<sign-form>]
<sign-form>	:=	{ + \| - }
<e-char>	:=	{ D \| d \| E \| e }

See:

A.12.6.1.0558 >FLOAT.

Rationale:

>FLOAT enables programs to read floating-point data in legible ASCII format. It accepts a much broader syntax than does the text interpreter since the latter defines rules for composing source programs whereas >FLOAT defines rules for accepting data. >FLOAT is defined as broadly as is feasible to permit input of data from Forth-2012 systems as well as other widely used standard programming environments.

This is a synthesis of common FORTRAN practice. Embedded spaces are explicitly forbidden in much scientific usage, as are other field separators such as comma or slash.

While >FLOAT is not required to treat a string of blanks as zero, this behavior is strongly encouraged, since a future version of this standard may include such a requirement.