595 lines
15 KiB
Plaintext
595 lines
15 KiB
Plaintext
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C. EXPERIMENTAL PROPOSALS
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APPENDIX C. EXPERIMENTAL PROPOSALS
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Since FORTH is an extensible language and subject to evolution,
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the Standard contains a section describing experimental
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proposals. FORTH users are encouraged to study, implement, and
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try these proposals to aid in the analysis of and the decision
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for or against future adoption into the Standard. Readers are
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cautioned that these proposals contain opinions and conclusions
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of the authors of the proposals and that these proposals may
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contain non-standard source code.
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65
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C. EXPERIMENTAL PROPOSALS
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SEARCH ORDER SPECIFICATION AND CONTROL
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WILLIAM F. RAGSDALE
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1 INTRODUCTION
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The method of selecting the order in which the dictionary is
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searched has grown from unchained vocabularies to the present use
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of chained vocabularies. Many techniques are in use for
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specification of the sequence in which multiple vocabularies may
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be searched. In order to offer generality and yet get precision
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in specification, this proposal is offered.
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2 DESCRIPTION
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The following functions are required:
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1. Two search orders exist. CONTEXT is the group of
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vocabularies searched during interpretation of text from the
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input stream. CURRENT is the single vocabulary into which
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new definitions are compiled, and from which FORGET
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operates.
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2. Empty CONTEXT to a minimum number of system words. These
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are just the words to further specify the search order.
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3. Add individual vocabularies into CONTEXT. The most recently
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added is searched first.
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4. Specify which single vocabulary will become CURRENT.
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The following optional functions aid the user:
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1. Display the word names of the first vocabulary in the
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CONTEXT search order.
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2. Display the vocabulary names comprising CURRENT and CONTEXT
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search orders.
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66
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C. EXPERIMENTAL PROPOSALS
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3 ADVANTAGES
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Use over the past year has demonstrated that the proposed
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methods may emulate the vocabulary selection of all other
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systems. The order is explicit by execution, may be interpreted
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and compiled, and is obvious from the declaration. The search
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order is specified at run-time rather than the time a new
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vocabulary is created.
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4 DISADVANTAGES
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By migrating to a common structure, vendors give up one
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point at which they may claim their product is better than
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others. Another drawback is that the number of CONTEXT
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vocabularies is fixed; older methods had an indefinite 'tree'
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structure. In practice, the branching of such a structure was
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very rarely greater than four.
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Forth words operate in a context sensitive environment, as
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word names may be redefined and have different definitions in
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different vocabularies. This proposal compounds the problem. By
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displaying the search order names, the user at least can readily
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verify the search order.
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5 IMPACT
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The text of the Forth 83 Standard has been carefully chosen
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for consistency and generality. However, no specification on how
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the search order is developed by the user is given. This
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omission is unavoidable, due to the diversity of contemporary
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practice. This proposal is intended to complete the Forth 83
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requirements in a fashion that exceeds all other methods.
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Previously standardized words continue in their use:
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VOCABULARY, FORTH, DEFINITIONS, and FORGET. However, this
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proposal assumes that vocabulary names are not IMMEDIATE .
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6 DEFINITIONS
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Search order:
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The sequence in which vocabularies are selected when
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locating a word by name in the dictionary. Consists of one
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transient and up to three resident vocabularies.
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Transient order:
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Execution of any vocabulary makes it the first vocabulary
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searched, replacing the previously selected transient
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vocabulary.
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67
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C. EXPERIMENTAL PROPOSALS
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Resident order:
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After searching the transient order, up to three additional
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vocabularies may be searched. The application program
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controls this selection.
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7 GLOSSARY
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ONLY -- ONLY
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Select just the ONLY vocabulary as both the transient
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vocabulary and resident vocabulary in the search order.
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FORTH -- ONLY
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The name of the primary vocabulary. Execution makes FORTH
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the transient vocabulary, the first in the search order, and
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thus replaces the previous transient vocabulary.
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ALSO -- ONLY
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The transient vocabulary becomes the first vocabulary in the
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resident portion of the search order. Up to the last two
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resident vocabularies will also be reserved, in order,
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forming the resident search order.
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ORDER -- ONLY
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Display the vocabulary names forming the search order in
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their present search order sequence. Then show the
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vocabulary into which new definitions will be placed.
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WORDS -- ONLY
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Display the word names in the transient vocabulary, starting
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with the most recent definition.
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FORGET -- ONLY
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Used in the form:
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FORGET <name>
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Delete from the dictionary <name> and all words added to the
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dictionary after <name> regardless of the vocabulary.
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Failure to find <name> is an error condition. An error
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condition also exists upon implicitly forgetting a
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vocabulary (due to its definition after <name>).
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DEFINITIONS -- ONLY
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Select the transient vocabulary as the current vocabulary
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into which subsequent definitions will be added.
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SEAL -- ONLY
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Delete all occurances of ONLY from the search order. The
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effect is that only specified application vocabularies will
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be searched.
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68
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C. EXPERIMENTAL PROPOSALS
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8 TYPICAL SOURCE CODE
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0 ( ALSO ONLY 82jun12 WFR )
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1 ( note the systems -FIND searches 1 to 5 vocabs in CONTEXT )
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2 VOCABULARY ONLY ONLY DEFINITIONS
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3 : ALSO ( slide transient into resident )
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4 CONTEXT DUP 2+ 6 CMOVE> ;
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5
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6 HERE 2+ ] ( alter run time from usual vocabulary )
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7 DOES> CONTEXT 8 ERASE DUP CONTEXT ! CONTEXT 8 + !
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8 ALSO EXIT [
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9 ' ONLY CFA ! ( Patch into ONLY; make NULL word )
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10 CREATE X ' EXIT >BODY X ! 41088 ' X NFA ! IMMEDIATE
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11 : FORTH FORTH ;
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12 : DEFINITIONS DEFINITIONS ; : FORGET FORGET ;
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13 : VOCABULARY VOCABULARY ; : ONLY ONLY ;
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14 : WORDS WORDS ;
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15
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0 ( ORDER 82jun12 WFR )
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1 : ORDER ( show the search order )
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2 10 SPACES CONTEXT 10 OVER + SWAP
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3 DO I @ ?DUP 0= ?LEAVE ID. 2 +LOOP
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4 10 SPACES CURRENT @ ID. ;
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6 ONLY FORTH ALSO DEFINITIONS
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9 EXAMPLES OF USE
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ONLY reduce search order to minimum
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FORTH search FORTH then ONLY
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ALSO EDITOR search EDITOR, FORTH then ONLY
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DEFINITIONS new definitions will be added into the EDITOR
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The same sequence would be compiled:
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: SETUP ONLY FORTH ALSO EDITOR DEFINITIONS ;
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10 REFERENCES
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W. F. Ragsdale, The 'ONLY' Concept for Vocabularies, Proceedings
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of the 1982 FORML Conference, pub. Forth Interest Group.
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C. EXPERIMENTAL PROPOSALS
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W. F. Ragsdale, fig-FORTH Installation Manual, Forth Interest
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Group.
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C. EXPERIMENTAL PROPOSALS
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DEFINITION FIELD ADDRESS CONVERSION OPERATORS
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by
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Kim R. Harris
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A. INTRODUCTION
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The standard provides a transportable way to obtain the
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compilation address of a definition in the dictionary of a FORTH
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system (cf., FIND and ' ). It also provides an operator to
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convert a compilation address to its corresponding parameter
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field address. However, the standard does not provide a
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transportable way to convert either of these addresses to the
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other fields of a definition. Since various FORTH
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implementations have different dictionary structures, a standard
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set of conversion operators would increase transportability and
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readability.
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A set of words is proposed which allows the conversion of any
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definitions field address to any other.
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B. GLOSSARY
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In the following words, the compilation address is either the
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source or the destination, so it is not indicated in the names.
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>BODY addr1 -- addr2 "to-body"
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addr2 is the parameter field address corresponding to the
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compilation address addr1.
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>NAME addr1 -- addr2 "to-name"
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addr2 is the name field address corresponding to the
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compilation address addr1.
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>LINK addr1 -- addr2 "to-link"
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addr2 is the link field address corresponding to the
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compilation address addr1.
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BODY> addr1 -- addr2 "from-body"
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addr2 is the compilation address corresponding to the
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parameter field address addr1.
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NAME> addr1 -- addr2 "from-name"
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addr2 is the compilation address corresponding to the name
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field address addr1.
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C. EXPERIMENTAL PROPOSALS
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LINK> addr1 -- addr2 "from-link"
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addr2 is the compilation address corresponding to the link
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field address addr1.
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The previous set of words is complete, but may be inefficient for
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going between two fields when one is not the compilation address.
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For greater efficiency, additional operators may be defined which
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name both the source and destination fields.
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N>LINK addr1 -- addr2 "name-to-link"
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addr2 is the link field address corresponding to the name
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field address addr1.
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L>NAME addr1 -- addr2 "link-to-name"
|
||
|
|
addr2 is the name field address corresponding to the link
|
||
|
|
field address addr1.
|
||
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|
||
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|
||
|
|
C. DISCUSSION
|
||
|
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|
||
|
|
The previous words provide a complete, consistent, and efficient
|
||
|
|
set of definition field address conversion operations. They can
|
||
|
|
be implemented in a FORTH system which uses any combination of
|
||
|
|
the following options for its dictionary structure:
|
||
|
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|
||
|
|
Link fields first or second.
|
||
|
|
Fixed or variable length name fields.
|
||
|
|
Additional fields in the definitions structure.
|
||
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|
||
|
|
Heads contiguous or separated from bodies.
|
||
|
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|
||
|
|
Indirect, direct, subroutine, or token threaded code.
|
||
|
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|
||
|
|
The words are compatible with this standard; their inclusion
|
||
|
|
would not require other changes to be made to the standard.
|
||
|
|
|
||
|
|
Disadvantages to including them in the standard include:
|
||
|
|
|
||
|
|
They add 6 to 8 more words to the standard.
|
||
|
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|
||
|
|
A standard program may not use all of them since it is not
|
||
|
|
allowed to access the name or link fields. However, this
|
||
|
|
does not disqualify them from being in the standard.
|
||
|
|
|
||
|
|
If a definition's head is not in the dictionary, an error
|
||
|
|
condition would exist. In this case, what action should the
|
||
|
|
words take in an implemented system?
|
||
|
|
|
||
|
|
The author of this experimental proposal recommends that FORTH
|
||
|
|
system implementors try them and that they be included in the
|
||
|
|
System Word Set of the next FORTH standard.
|
||
|
|
|
||
|
|
|
||
|
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|
||
|
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|
||
|
|
|
||
|
|
|
||
|
|
72
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
C. EXPERIMENTAL PROPOSALS
|
||
|
|
|
||
|
|
|
||
|
|
D. SOURCE CODE EXAMPLE
|
||
|
|
|
||
|
|
High level source code is shown below for a very simple
|
||
|
|
dictionary structure. This code assumes a FORTH system which
|
||
|
|
uses indirect threaded code, heads contiguous to bodies, and a
|
||
|
|
definition structure of the following format:
|
||
|
|
|
||
|
|
Name field, 4 bytes long, fixed length.
|
||
|
|
Link field, 2 bytes long.
|
||
|
|
Code field, 2 bytes long.
|
||
|
|
Parameter field, variable length.
|
||
|
|
|
||
|
|
: >BODY ( acf -- apf ) 2+ ;
|
||
|
|
: BODY> ( apf -- acf ) 2- ;
|
||
|
|
: >LINK ( acf -- alf ) 2- ;
|
||
|
|
: LINK> ( alf -- acf ) 2- ;
|
||
|
|
: >NAME ( acf -- anf ) 6 - ;
|
||
|
|
: NAME> ( anf -- alf ) 6 + ;
|
||
|
|
: N>LINK ( anf -- alf ) 4 + ;
|
||
|
|
: L>NAME ( alf -- anf ) 4 - ;
|
||
|
|
|
||
|
|
|
||
|
|
E. EXAMPLES OF USE
|
||
|
|
|
||
|
|
No examples are given because their use should be obvious.
|
||
|
|
|
||
|
|
|
||
|
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|
||
|
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|
||
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|
||
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|
||
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|
||
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|
||
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|
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|
||
|
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|
||
|
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|
||
|
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|
||
|
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|
||
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|
||
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|
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|
||
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|
||
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|
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|
||
|
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|
||
|
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|
||
|
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|
||
|
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|
||
|
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|
||
|
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|
||
|
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|
||
|
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|
||
|
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|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
73
|
||
|
|
|