Commit b170343f8183ed2d469bf3e598a21b9fc7a26f0a - Arboretuum

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README.markdown less more

0		The Arboretuum Programming Language
1		===================================
2
3		March 2008, Chris Pressey, Cat's Eye Technologies.
4
5		Description
6		-----------
7
8		Arboretuum is a language based on an experimental variant of
9		tree-rewriting which we call forest-rewriting. Appropriate to its name,
10		during forest-rewriting, multiple trees (specifically, a finite set) are
11		rewritten. Each tree is labelled with a name; a rewriting pattern can
12		refer to multiple trees, and must match all of them simultaneously in
13		order for a replacement to occur.
14
15		As an experiment, Arboretuum was not entirely a success.
16		Forest-rewriting unfortunately turned out to be insufficient for what I
17		wanted to apply it to, namely compiler specification. The idea was to
18		have each tree associated with some data structure used in the
19		compilation process (AST, symbol table, output buffer, etc.) However, it
20		became apparent that, by itself, forest-rewriting could not synchronize
21		the data across the trees the way it would need to be synchronized in a
22		real compiler. I plan to tackle the problem again, with a different
23		variation on rewriting, in a future project.
24
25		Regardless, Arboretuum is Turing-complete, as tree-rewriting is simply a
26		special case of forest-rewriting: just have one tree in the forest.
27
28		Implementation
29		--------------
30
31		I will refer you to the reference implementation of Arboretuum for
32		details on the semantics of the language. Ordinarily I frown upon this
33		sort of practice — normatively defining a language by an implementation
34		rather than by a specification — but the interests of brevity, the
35		experimental tack of the project, the unsuccessful outcome of the
36		experiment, and the relative well-definedness of the implementation
37		language (the purely functional subset of R5RS Scheme) conspire to
38		make the consequences of this choice less painful than usual.
39
40		The reference implementation comprises the following files:
41
42		- `preprocess.scm`
43
44		Pre-processes the input program into an internal format suitable for
45		forest-rewriting.
46
47		- `unify.scm`
48
49		Implementation of the unification algorithm which is used to match
50		the pattern part of rewriting rules to the forest.
51
52		- `forest-rewrite.scm`
53
54		Implements the forest-rewriting process proper.
55
56		- `utils.scm`
57
58		Miscellanous support procedures, including `mergesort`,
59		`vector-store` (a side-effect-free alternative to `vector-set!`),
60		`print` and `test`.
61
62		In addition, the following supplementary files which are not definitive
63		w.r.t. the Arboretuum language are included in the project:
64
65		- `tests.scm`
66
67		Gives a set of unit tests to confirm the absence of certain
68		erroneous behaviours. (Obviously, no number of unit tests could
69		confirm the absence of errors...)
70
71		- `tree-rewrite.scm`
72
73		Some basic tree-rewriting code, to provide contrast between it's
74		complexity and that of forest rewriting.
75
76		Note that the Scheme implementation of algorithms in the above files are
77		to be taken as pedantic rather than efficient. They are meant to be
78		read (perhaps even enjoyed?) and only incidentally to be executed.
79
80		History
81		-------
82
83		This project was begun in January 2006. I'd been meaning to release it
84		for a while before actually doing so in March of 2008.
85
86		Happy forest-rewriting!
87
88		-Chris Pressey
89		Cat's Eye Technologies
90		March 4, 2008
91		Chicago, Illinois, USA
	0	The Arboretuum Programming Language
	1	===================================
	2
	3	March 2008, Chris Pressey, Cat's Eye Technologies.
	4
	5	Description
	6	-----------
	7
	8	Arboretuum is a language based on an experimental variant of
	9	tree-rewriting which we call forest-rewriting. Appropriate to its name,
	10	during forest-rewriting, multiple trees (specifically, a finite set) are
	11	rewritten. Each tree is labelled with a name; a rewriting pattern can
	12	refer to multiple trees, and must match all of them simultaneously in
	13	order for a replacement to occur.
	14
	15	As an experiment, Arboretuum was not entirely a success.
	16	Forest-rewriting unfortunately turned out to be insufficient for what I
	17	wanted to apply it to, namely compiler specification. The idea was to
	18	have each tree associated with some data structure used in the
	19	compilation process (AST, symbol table, output buffer, etc.) However, it
	20	became apparent that, by itself, forest-rewriting could not synchronize
	21	the data across the trees the way it would need to be synchronized in a
	22	real compiler. I plan to tackle the problem again, with a different
	23	variation on rewriting, in a future project.
	24
	25	Regardless, Arboretuum is Turing-complete, as tree-rewriting is simply a
	26	special case of forest-rewriting: just have one tree in the forest.
	27
	28	Implementation
	29	--------------
	30
	31	I will refer you to the reference implementation of Arboretuum for
	32	details on the semantics of the language. Ordinarily I frown upon this
	33	sort of practice — normatively defining a language by an implementation
	34	rather than by a specification — but the interests of brevity, the
	35	experimental tack of the project, the unsuccessful outcome of the
	36	experiment, and the relative well-definedness of the implementation
	37	language (the purely functional subset of R5RS Scheme) conspire to
	38	make the consequences of this choice less painful than usual.
	39
	40	The reference implementation comprises the following files:
	41
	42	- `preprocess.scm`
	43
	44	Pre-processes the input program into an internal format suitable for
	45	forest-rewriting.
	46
	47	- `unify.scm`
	48
	49	Implementation of the unification algorithm which is used to match
	50	the pattern part of rewriting rules to the forest.
	51
	52	- `forest-rewrite.scm`
	53
	54	Implements the forest-rewriting process proper.
	55
	56	- `utils.scm`
	57
	58	Miscellanous support procedures, including `mergesort`,
	59	`vector-store` (a side-effect-free alternative to `vector-set!`),
	60	`print` and `test`.
	61
	62	In addition, the following supplementary files which are not definitive
	63	w.r.t. the Arboretuum language are included in the project:
	64
	65	- `tests.scm`
	66
	67	Gives a set of unit tests to confirm the absence of certain
	68	erroneous behaviours. (Obviously, no number of unit tests could
	69	confirm the absence of errors...)
	70
	71	- `tree-rewrite.scm`
	72
	73	Some basic tree-rewriting code, to provide contrast between it's
	74	complexity and that of forest rewriting.
	75
	76	Note that the Scheme implementation of algorithms in the above files are
	77	to be taken as pedantic rather than efficient. They are meant to be
	78	read (perhaps even enjoyed?) and only incidentally to be executed.
	79
	80	History
	81	-------
	82
	83	This project was begun in January 2006. I'd been meaning to release it
	84	for a while before actually doing so in March of 2008.
	85
	86	Happy forest-rewriting!
	87
	88	-Chris Pressey
	89	Cat's Eye Technologies
	90	March 4, 2008
	91	Chicago, Illinois, USA

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UNLICENSE less more

	0	This is free and unencumbered software released into the public domain.
	1
	2	Anyone is free to copy, modify, publish, use, compile, sell, or
	3	distribute this software, either in source code form or as a compiled
	4	binary, for any purpose, commercial or non-commercial, and by any
	5	means.
	6
	7	In jurisdictions that recognize copyright laws, the author or authors
	8	of this software dedicate any and all copyright interest in the
	9	software to the public domain. We make this dedication for the benefit
	10	of the public at large and to the detriment of our heirs and
	11	successors. We intend this dedication to be an overt act of
	12	relinquishment in perpetuity of all present and future rights to this
	13	software under copyright law.
	14
	15	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
	16	EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
	17	MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
	18	IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
	19	OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
	20	ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
	21	OTHER DEALINGS IN THE SOFTWARE.
	22
	23	For more information, please refer to <http://unlicense.org/>

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src/forest-rewrite.scm less more

1	1	; Forest Rewriting
2	2	; Chris Pressey, late January 2006
3	3	;
4
5		; Copyright (c)2008 Cat's Eye Technologies. All rights reserved.
	4	; This work is in the public domain. See the file UNLICENSE for more
	5	; information.
6	6	;
7		; Redistribution and use in source and binary forms, with or without
8		; modification, are permitted provided that the following conditions
9		; are met:
10		;
11		; 1. Redistributions of source code must retain the above copyright
12		; notices, this list of conditions and the following disclaimer.
13		; 2. Redistributions in binary form must reproduce the above copyright
14		; notices, this list of conditions, and the following disclaimer in
15		; the documentation and/or other materials provided with the
16		; distribution.
17		; 3. Neither the names of the copyright holders nor the names of their
18		; contributors may be used to endorse or promote products derived
19		; from this software without specific prior written permission.
20		;
21		; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22		; ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES INCLUDING, BUT NOT
23		; LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
24		; FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
25		; COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
26		; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
27		; BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28		; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
29		; CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30		; LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
31		; ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
32		; POSSIBILITY OF SUCH DAMAGE.
33	7
34	8	;
35	9	; Given a term, a pattern to look for in that term, a replacement pattern,

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src/preprocess.scm less more

1	1	; Preprocessor for Forest Rewriter
2	2	; Chris Pressey, sometime late January 2006
3	3	;
4
5		; Copyright (c)2008 Cat's Eye Technologies. All rights reserved.
	4	; This work is in the public domain. See the file UNLICENSE for more
	5	; information.
6	6	;
7		; Redistribution and use in source and binary forms, with or without
8		; modification, are permitted provided that the following conditions
9		; are met:
10		;
11		; 1. Redistributions of source code must retain the above copyright
12		; notices, this list of conditions and the following disclaimer.
13		; 2. Redistributions in binary form must reproduce the above copyright
14		; notices, this list of conditions, and the following disclaimer in
15		; the documentation and/or other materials provided with the
16		; distribution.
17		; 3. Neither the names of the copyright holders nor the names of their
18		; contributors may be used to endorse or promote products derived
19		; from this software without specific prior written permission.
20		;
21		; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22		; ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES INCLUDING, BUT NOT
23		; LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
24		; FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
25		; COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
26		; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
27		; BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28		; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
29		; CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30		; LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
31		; ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
32		; POSSIBILITY OF SUCH DAMAGE.
33	7
34	8	;
35	9	; The goal here is to allow the compound-rules to be specified in a nicer,

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src/tests.scm less more

1	1	; Test suite for forest-rewriting project
2	2	; Chris Pressey, sometime late January 2006
3	3	;
4
5		; Copyright (c)2008 Cat's Eye Technologies. All rights reserved.
	4	; This work is in the public domain. See the file UNLICENSE for more
	5	; information.
6	6	;
7		; Redistribution and use in source and binary forms, with or without
8		; modification, are permitted provided that the following conditions
9		; are met:
10		;
11		; 1. Redistributions of source code must retain the above copyright
12		; notices, this list of conditions and the following disclaimer.
13		; 2. Redistributions in binary form must reproduce the above copyright
14		; notices, this list of conditions, and the following disclaimer in
15		; the documentation and/or other materials provided with the
16		; distribution.
17		; 3. Neither the names of the copyright holders nor the names of their
18		; contributors may be used to endorse or promote products derived
19		; from this software without specific prior written permission.
20		;
21		; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22		; ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES INCLUDING, BUT NOT
23		; LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
24		; FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
25		; COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
26		; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
27		; BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28		; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
29		; CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30		; LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
31		; ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
32		; POSSIBILITY OF SUCH DAMAGE.
33	7
34	8
35	9	(load "utils.scm");--------------------------------------------------------

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src/tree-rewrite.scm less more

1	1	; Bottom-Up Tree-Rewriting (Term-Rewriting)
2	2	; Chris Pressey, sometime late January 2006
3	3	;
4
5		; Copyright (c)2008 Cat's Eye Technologies. All rights reserved.
	4	; This work is in the public domain. See the file UNLICENSE for more
	5	; information.
6	6	;
7		; Redistribution and use in source and binary forms, with or without
8		; modification, are permitted provided that the following conditions
9		; are met:
10		;
11		; 1. Redistributions of source code must retain the above copyright
12		; notices, this list of conditions and the following disclaimer.
13		; 2. Redistributions in binary form must reproduce the above copyright
14		; notices, this list of conditions, and the following disclaimer in
15		; the documentation and/or other materials provided with the
16		; distribution.
17		; 3. Neither the names of the copyright holders nor the names of their
18		; contributors may be used to endorse or promote products derived
19		; from this software without specific prior written permission.
20		;
21		; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22		; ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES INCLUDING, BUT NOT
23		; LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
24		; FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
25		; COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
26		; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
27		; BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28		; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
29		; CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30		; LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
31		; ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
32		; POSSIBILITY OF SUCH DAMAGE.
33	7
34	8	;
35	9	; Try unifying the pattern part of the given rule with the given term;

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src/unify.scm less more

1	1	; Simple support for unification & pattern matching
2	2	; Chris Pressey, late January 2006
3	3	;
4
5		; Copyright (c)2008 Cat's Eye Technologies. All rights reserved.
	4	; This work is in the public domain. See the file UNLICENSE for more
	5	; information.
6	6	;
7		; Redistribution and use in source and binary forms, with or without
8		; modification, are permitted provided that the following conditions
9		; are met:
10		;
11		; 1. Redistributions of source code must retain the above copyright
12		; notices, this list of conditions and the following disclaimer.
13		; 2. Redistributions in binary form must reproduce the above copyright
14		; notices, this list of conditions, and the following disclaimer in
15		; the documentation and/or other materials provided with the
16		; distribution.
17		; 3. Neither the names of the copyright holders nor the names of their
18		; contributors may be used to endorse or promote products derived
19		; from this software without specific prior written permission.
20		;
21		; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22		; ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES INCLUDING, BUT NOT
23		; LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
24		; FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
25		; COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
26		; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
27		; BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28		; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
29		; CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30		; LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
31		; ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
32		; POSSIBILITY OF SUCH DAMAGE.
33	7
34	8	;
35	9	; Return #t if the given pattern is a variable, #f otherwise.

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src/utils.scm less more

1	1	; Utility functions used by forest-rewriting project
2	2	; Chris Pressey, late January 2006
3	3	;
4
5		; Copyright (c)2008 Cat's Eye Technologies. All rights reserved.
	4	; This work is in the public domain. See the file UNLICENSE for more
	5	; information.
6	6	;
7		; Redistribution and use in source and binary forms, with or without
8		; modification, are permitted provided that the following conditions
9		; are met:
10		;
11		; 1. Redistributions of source code must retain the above copyright
12		; notices, this list of conditions and the following disclaimer.
13		; 2. Redistributions in binary form must reproduce the above copyright
14		; notices, this list of conditions, and the following disclaimer in
15		; the documentation and/or other materials provided with the
16		; distribution.
17		; 3. Neither the names of the copyright holders nor the names of their
18		; contributors may be used to endorse or promote products derived
19		; from this software without specific prior written permission.
20		;
21		; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22		; ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES INCLUDING, BUT NOT
23		; LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
24		; FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
25		; COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
26		; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
27		; BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28		; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
29		; CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30		; LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
31		; ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
32		; POSSIBILITY OF SUCH DAMAGE.
33	7
34	8	;
35	9	; Sort a list using mergesort.