B.3 DATA TYPES IN STACK NOTATION

Table 11 gives a description of the Standard Forth notation used to refer to the different data types that may appear in stack notation or descriptions in this manual. Additional tables in this section describe other notational conventions.

Table 11: Notation for the data type of stack arguments

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Some data types are sub-types of other data types. Figure 16 shows the hierarchy for sin- gle-cell and double-cell types. Any Forth definition that accepts an argument of a type shown in the figure must also accept all the subtypes below it. For example, a word with an input stack argument of type n also accepts arguments of type +n and char.

Figure 16. Hierarchy of data types

Standard Forth does not require data-type checking, and most implementations do not include it among their standard functions. Also, most implementations do not include arithmetic error checking on standard math functions (such as overflow on a multiply operation). The reason for both of these restrictions is that error checking and data-type checking on low-level functions could be prohibitively costly in execution time. Most Forth implementations do support whatever hardware error-detection functions exist, such as a trap for divide by zero, or the various exceptions signaled by the 80387/80486 floating-point processor. An application may, of course, build in error checking and/or type checking at any level deemed necessary, simply by redefining the words in question and adding an outer layer of protection.

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B.4 FLAGS AND IOR CODES

Procedures that accept flags as input arguments shall treat zero as false, and any non-zero value as true. A flag returned as an argument is a well-formed flag with all bits zero (false), or all bits one (true).

Certain device control and other functions return an ior (I/O Result) to report the results of an operation. An ior may be treated as a flag, in the sense that a non-zero value is true; however, it is not necessarily a well-formed flag, because its specific value often is used to convey additional information. A returned value of zero for an ior shall mean successful completion (i.e., no error); non-zero values may indicate an error condition or other abnormal status, and are device dependent.

B.5 FORTH GLOSSARY NOTATION

Words described in this manual are grouped functionally. An alphabetical list of all words is given in Appendix C.

Each entry consists of two parts: an index line and a semantic (behavioral) description of the word. The index line is a single-line entry containing, from left to right:

!Definition name, in upper-case, monospaced, boldface letters;

!Stack behavior (the notation follows the conventions described in Sections B.3 and B.4, above).

The first paragraph of the behavioral description concludes with the natural-language pronunciation of the word (shown in distinctive type), if it is not obvious.

A word’s behavior may be context dependent. The behavior(s) for each such word are described, as applicable, for:

Compiling An action taken by the system when adding to the Forth dictionary.

name Execution The behavior of name when executed, where name is an instance of a class of words created by a defining word (see Section 4.2).

Interpreting An action taken by the system when the name of a word is encountered by the text interpreter in interpretation state.

Run-time The behavior executed by the system.

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While many words (such as defining words and compiler directives) possess specific compiling behaviors, the default compilation behavior of a word is to append its execution behavior to the current definition. Separate behaviors in different modes will be shown, where they differ.

Some words will be executed (i.e., will perform their behavior) when encountered in compiling mode. In Forth, these are known as immediate words. If execution of such a word will cause some run-time action in the word being compiled, this is shown as a separate run-time behavior.

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