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0 The Etcha Programming Language
1 ==============================
2
3 _Try it online_ [@ catseye.tc](https://catseye.tc/installation/Etcha)
4 | _Wiki entry_ [@ esolangs.org](https://esolangs.org/wiki/Etcha)
5 | _See also:_ [Whothm](https://github.com/catseye/Whothm#readme)
6 ∘ [Wunnel](https://github.com/catseye/Wunnel#readme)
7 ∘ [Gemooy](https://github.com/catseye/Gemooy#readme)
8
9 - - - -
10
11 Introduction
12 ------------
13
14 Etcha is an esoteric programming language based on Jeffry Johnston's
15 [BitChanger](http://www.esolangs.org/wiki/BitChanger). Like BitChanger,
16 Etcha has four instructions, two of which are used to form
17 Brainfuck-like while-loops. Unlike BitChanger, Etcha has a 2-dimensional
18 storage model based on turtle graphics, which permits it to be
19 immediately used for an alternative purpose: graphical composition.
20 Unlike a classical turtle in a language such as LOGO however, the turtle
21 in Etcha is an integral part of the computation, playing a role similar
22 to the tape head of a Turing machine.
23
24 Instructions
25 ------------
26
27 - `+` -- equivalent to FD 1
28 - `>` -- equivalent to RT 90; toggles PU/PD every 4 executions
29 - `[` -- equivalent to While
30 - `]` -- equivalent to Wend
31
32 In Etcha, instructions control a turtle. The turtle exists vis-a-vis an
33 unbounded Cartesian grid called the playfield. The turtle has a position
34 in that it occupies exactly one of the points on the playfield (which
35 are referred to as pixels). Each pixel has a state, which is either
36 black or white; all pixels are initially black.
37
38 The turtle also has an orientation which describes the direction it
39 would move in should it travel forward. Unlike a conventional turtle,
40 because of its Cartesian context, there are only four possible
41 orientations which the Etcha turtle can possess: north, east, south, and
42 west, corresponding to headings of 0, 90, 180, and 270 degrees. When an
43 Etcha program starts, the turtle is initially oriented north. Because
44 position is relative, it doesn't matter where the turtle is initially
45 located, but solely for psychological satisfaction we can say that it is
46 initially situated in the very center of this unbounded Cartesian grid.
47
48 The turtle is also equipped with a pen, which has a pen mode and a pen
49 position. The pen mode is always XOR, meaning that when moving forward
50 by execution of `+`, the state of the pixel that was previously occupied
51 by the turtle gets inverted (from black to white, or vice versa.) The
52 pen position may be up or down. It is initially down. Every fourth time
53 an `>` instruction is executed, the pen's position is toggled from up to
54 down or vice versa. These executions need not be consecutive; there may
55 be any number of intervening instructions executed.
56
57 Examples
58 --------
59
60 -> Tests for functionality "Interpret Etcha Program"
61
62 -> Functionality "Interpret Etcha Program" is implemented by shell
63 -> command "java -cp bin tc.catseye.etcha.Main %(test-body-file)"
64
65 | >+++>+++>+++>+++>[+]>>>>+
66 = ----
67 = #####
68 = #
69 = #
70 = ###
71 = ----
72
73 Computational Class
74 -------------------
75
76 Etcha is Turing-complete if BitChanger is, because we can easily
77 translate any BitChanger program into an equivalent Etcha program. Let
78 the Etcha program begin with `>>>>`, to initially lift the pen. The
79 BitChanger instruction `<` is translated to the Etcha instructions
80 `>>>+>>>>>`, and the BitChanger instruction `}` is translated to
81 `>>>>>+>>>`. The instructions `[` and `]` remain the same. The relation
82 between the BitChanger tape state and the Etcha playfield is quite
83 literal; the y dimension of the grid is simply ignored.
84
85 Implementation
86 --------------
87
88 In a particular implementation of Etcha on a microcomputer with a finite
89 storage, the playfield cannot be truly unbounded, and there will come a
90 point in a long enough program execution, entirely dependent on the
91 capabilities of the hardware and the implementation, where a pixel
92 change cannot be correctly stored. The behaviour after this point is
93 undefined. *Such (m)icro(c)omputer implementations of Etcha may be
94 marketed under the name "MC Etcha"*.
95
96 Cat's Eye Technologies provides an implementation of Etcha written in
97 the Java[TM] programming language. This implementation attempts to
98 demonstrate that the Model-View-Controller design pattern can be applied
99 not only to user interfaces, but also to programming language
100 interpreters. The Model is the state of the program (which is also the
101 state of the Turtle graphics engine.) The View is the interpreter's
102 interpretation of that state, and the Controller is the interpreter's
103 behaviour with respect to the View. For example, the Model exposes the
104 pen up/down semantics, but it is the Controller that implements the rule
105 that `>>>>` toggles the pen position.
106
107 Cat's Eye Technologies' ridiculously over-engineered implementation of
108 Etcha is in the public domain.
109
110 Happy Etchin'!
111 Chris Pressey
112 October 4th, 2009
113 Mold City, USA
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README.md less more
0 The Etcha Programming Language
1 ==============================
2
3 _Try it online_ [@ catseye.tc](https://catseye.tc/installation/Etcha)
4 | _Wiki entry_ [@ esolangs.org](https://esolangs.org/wiki/Etcha)
5 | _See also:_ [Whothm](https://github.com/catseye/Whothm#readme)
6 ∘ [Wunnel](https://github.com/catseye/Wunnel#readme)
7 ∘ [Gemooy](https://github.com/catseye/Gemooy#readme)
8
9 - - - -
10
11 Introduction
12 ------------
13
14 Etcha is an esoteric programming language based on Jeffry Johnston's
15 [BitChanger](http://www.esolangs.org/wiki/BitChanger). Like BitChanger,
16 Etcha has four instructions, two of which are used to form
17 Brainfuck-like while-loops. Unlike BitChanger, Etcha has a 2-dimensional
18 storage model based on turtle graphics, which permits it to be
19 immediately used for an alternative purpose: graphical composition.
20 Unlike a classical turtle in a language such as LOGO however, the turtle
21 in Etcha is an integral part of the computation, playing a role similar
22 to the tape head of a Turing machine.
23
24 Instructions
25 ------------
26
27 - `+` -- equivalent to FD 1
28 - `>` -- equivalent to RT 90; toggles PU/PD every 4 executions
29 - `[` -- equivalent to While
30 - `]` -- equivalent to Wend
31
32 In Etcha, instructions control a turtle. The turtle exists vis-a-vis an
33 unbounded Cartesian grid called the playfield. The turtle has a position
34 in that it occupies exactly one of the points on the playfield (which
35 are referred to as pixels). Each pixel has a state, which is either
36 black or white; all pixels are initially black.
37
38 The turtle also has an orientation which describes the direction it
39 would move in should it travel forward. Unlike a conventional turtle,
40 because of its Cartesian context, there are only four possible
41 orientations which the Etcha turtle can possess: north, east, south, and
42 west, corresponding to headings of 0, 90, 180, and 270 degrees. When an
43 Etcha program starts, the turtle is initially oriented north. Because
44 position is relative, it doesn't matter where the turtle is initially
45 located, but solely for psychological satisfaction we can say that it is
46 initially situated in the very center of this unbounded Cartesian grid.
47
48 The turtle is also equipped with a pen, which has a pen mode and a pen
49 position. The pen mode is always XOR, meaning that when moving forward
50 by execution of `+`, the state of the pixel that was previously occupied
51 by the turtle gets inverted (from black to white, or vice versa.) The
52 pen position may be up or down. It is initially down. Every fourth time
53 an `>` instruction is executed, the pen's position is toggled from up to
54 down or vice versa. These executions need not be consecutive; there may
55 be any number of intervening instructions executed.
56
57 Examples
58 --------
59
60 -> Tests for functionality "Interpret Etcha Program"
61
62 -> Functionality "Interpret Etcha Program" is implemented by shell
63 -> command "java -cp bin tc.catseye.etcha.Main %(test-body-file)"
64
65 | >+++>+++>+++>+++>[+]>>>>+
66 = ----
67 = #####
68 = #
69 = #
70 = ###
71 = ----
72
73 Computational Class
74 -------------------
75
76 Etcha is Turing-complete if BitChanger is, because we can easily
77 translate any BitChanger program into an equivalent Etcha program. Let
78 the Etcha program begin with `>>>>`, to initially lift the pen. The
79 BitChanger instruction `<` is translated to the Etcha instructions
80 `>>>+>>>>>`, and the BitChanger instruction `}` is translated to
81 `>>>>>+>>>`. The instructions `[` and `]` remain the same. The relation
82 between the BitChanger tape state and the Etcha playfield is quite
83 literal; the y dimension of the grid is simply ignored.
84
85 Implementation
86 --------------
87
88 In a particular implementation of Etcha on a microcomputer with a finite
89 storage, the playfield cannot be truly unbounded, and there will come a
90 point in a long enough program execution, entirely dependent on the
91 capabilities of the hardware and the implementation, where a pixel
92 change cannot be correctly stored. The behaviour after this point is
93 undefined. *Such (m)icro(c)omputer implementations of Etcha may be
94 marketed under the name "MC Etcha"*.
95
96 Cat's Eye Technologies provides an implementation of Etcha written in
97 the Java[TM] programming language. This implementation attempts to
98 demonstrate that the Model-View-Controller design pattern can be applied
99 not only to user interfaces, but also to programming language
100 interpreters. The Model is the state of the program (which is also the
101 state of the Turtle graphics engine.) The View is the interpreter's
102 interpretation of that state, and the Controller is the interpreter's
103 behaviour with respect to the View. For example, the Model exposes the
104 pen up/down semantics, but it is the Controller that implements the rule
105 that `>>>>` toggles the pen position.
106
107 Cat's Eye Technologies' ridiculously over-engineered implementation of
108 Etcha is in the public domain.
109
110 Happy Etchin'!
111 Chris Pressey
112 October 4th, 2009
113 Mold City, USA