LOCALS

Section: Miscellaneous Library Functions (3X)
Updated: August 1, 1990
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NAME

locals - tile kernel argument binding and local variable functions

SYNOPSIS

locals

DESCRIPTION

The tile kernel support for argument binding and local variables in colon definitions. The tile forth virtual machine model support building and disposing of argument frames. The frame is build directly on the parameter stack. This minimizes the amount of data that has to be moved. Arguments and local variables are accessed by a frame pointer. The frame pointer is automatically maintained by the virtual machine. On the exit of a colon definition using "locals" the frame is disposed and return values moved to their correct position on the parameter stack. Other forth implementation build the frame on a separate stack or on the return stack. This implementation is much more efficient when the number of return values is often less than the number of arguments and local variables.

code -> ( x -- ) compilation: Assigns an argument or local variable with the value "x". Used in the following form:
<value> -> <frame-variable>
The word after the assignment operator must be a <frame-variable> otherwise an error is accounted. The compiler does not check this error situation.
code exit ( -- ) compilation: Performs the equivalent action of the normal "exit" but also restores the stack after argument binding and local variables.
vocabulary locals ( -- ): Vocabulary containing the argument binding and local variable extension. Include into the vocabulary search structure, "context", to allow access to these extensions.
code { ( -- ) immediate compilation: Starts the named argument and local variable compiler. Used in the following forms:
{ <argument-names> | <local-names> -- <any> }
or
{ <argument-names> -- <any> }
or
{ | <local-names> -- <any> }
The different parts are as shown optional. The only restriction is that the definition of argument and local variable names is terminated by "}" or "--". In the "--" case characters until "}" are skipped and may be regarded as a comment. Return values are not named.

INTERNALS

The following set of functions are mainly used to implement the argument binding and local variable frame management.

code (link) ( arguments -- frame old-frame-pointer) compilation: Compiled by "{" to perform the run-time action of building the argument and local variable frame. The frame is built directly on the parameter stack to minimize data movement. The frame consists of the arguments and stack area for the local variables. The old frame pointer is stored on the top of the parameter stack, making lexical levels possible. A pointer to the top of the frame, i.e., the parameter stack top, is saved on the return stack so that return values may be moved down to their correct position on the parameter stack and the old frame pointer restored. The frame pointer will point to the first element below the first argument. This element will become the top of stack if no values are returned.
code (local) ( -- addr) compilation: Returns the address of an argument or local variable within the current frame using an inline literal offset. To access the address of the first variable in the frame the offset should be one.
code (local!) ( value -- ) compilation: Stores "value" to an argument or local variable within the current argument frame using an inline literal offset. To assign the first variable in the frame the offset should be one.
code (local@) ( -- value) compilation: Access the value of an argument or local variable within the current argument frame using an inline literal offset. To access the value of the first variable in the frame the offset should be one.
code (unlink) ( frame return -- return) compilation: Drops the frame and move the return values down. The old frame pointer is restored.
code (unlink;) ( frame return -- return) compilation: Drops the frame and move the return values down. The old frame pointer is restored. Leaves the colon definition. Compiled by the word ";".
code (unlink>) ( frame return -- return) compilation: Drops the frame and move the return values down. The old frame pointer is restored. Assigns the "code" type of the latest definition and leaves the colon definition. Compiled by the word "does>".

NOTE

The function list is sorted in ASCII order. The type and mode of the entry is indicated together with the parameter stack effect.

COPYING

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the author instead of in the original English.

AUTHOR

Mikael R.K. Patel
Computer Aided Design Laboratory (CADLAB)
Department of Computer and Information Science
Linkoping University
S-581 83 LINKOPING
SWEDEN
Email: mip@ida.liu.se
omp!

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