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README.md
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README.md
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@ -19,6 +19,7 @@
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## Usage
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Type lambda expressions into the prompt, and Lamb will evaluate them. \
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Use your `\` (backslash) key to type a `λ`. \
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To define macros, use `=`. For example,
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@ -30,22 +31,30 @@ To define macros, use `=`. For example,
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Note that there are spaces in `λa.a F T`. With no spaces, `aFT` will be parsed as one variable. \
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Lambda functions can only take single-letter, lowercase arguments. `λA.A` is not valid syntax. \
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Unbound variables (upper and lower case) that aren't macros will become free variables. Free variables will be shown with a `'`, like `a'`.
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Free variables will be shown with a `'`, like `a'`.
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Be careful, macros are case-sensitive. If you define a macro `MAC` and accidentally write `mac` in the prompt, `mac` will become a free variable.
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Macros are case-sensitive. If you define a macro `MAC` and accidentally write `mac` in the prompt, `mac` will become a free variable.
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Numbers will automatically be converted to Church numerals. For example, the following line will reduce to `T`.
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```
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==> 3 NOT F
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```
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If an expression takes too long to evaluate, you may interrupt reduction with `Ctrl-C`.
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If an expression takes too long to evaluate, you may interrupt reduction with `Ctrl-C`. \
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Exit the prompt with `Ctrl-C` or `Ctrl-D`.
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There are many useful macros in [macros.lamb](./macros.lamb). Load them with the `:load` command:
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```
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==> :load macros.lamb
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```
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Have fun!
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-------------------------------------------------
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## Commands
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Lamb comes with a few commands. Prefix them with a `:`
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Lamb understands many commands. Prefix them with a `:` in the prompt.
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`:help` Prints a help message
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@ -60,7 +69,9 @@ Lamb comes with a few commands. Prefix them with a `:`
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`:clearmacros` Delete all macros
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`:save [filename]` \
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`:load [filename]` Save or load the current environment to a file. The lines in a file look exactly the same as regular entries in the prompt, but must only contain macro definitions.
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`:load [filename]` \
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Save or load macros from a file.
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The lines in a file look exactly the same as regular entries in the prompt, but can only contain macro definitions. See [macros.lamb](./macros.lamb) for an example.
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-------------------------------------------------
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@ -1,66 +1,29 @@
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if __name__ != "__main__":
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raise ImportError("lamb.__main__ should never be imported. Run it directly.")
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from prompt_toolkit import PromptSession
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from prompt_toolkit.completion import WordCompleter
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from prompt_toolkit import print_formatted_text as printf
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from prompt_toolkit.formatted_text import FormattedText
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from prompt_toolkit.formatted_text import to_plain_text
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from prompt_toolkit.key_binding import KeyBindings
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from prompt_toolkit.lexers import Lexer
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from pyparsing import exceptions as ppx
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import lamb
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# Simple lexer for highlighting.
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# Improve this later.
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class LambdaLexer(Lexer):
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def lex_document(self, document):
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def inner(line_no):
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return [("class:text", str(document.lines[line_no]))]
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return inner
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lamb.utils.show_greeting()
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# Replace "\" with pretty "λ"s
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bindings = KeyBindings()
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@bindings.add("\\")
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def _(event):
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event.current_buffer.insert_text("λ")
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r = lamb.Runner(
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prompt_session = PromptSession(
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style = lamb.utils.style,
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lexer = LambdaLexer(),
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key_bindings = bindings
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lexer = lamb.utils.LambdaLexer(),
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key_bindings = lamb.utils.bindings
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),
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prompt_message = FormattedText([
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("class:prompt", "==> ")
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])
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)
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r.run_lines([
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"T = λab.a",
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"F = λab.b",
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"NOT = λa.(a F T)",
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"AND = λab.(a b F)",
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"OR = λab.(a T b)",
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"XOR = λab.(a (NOT b) b)",
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"M = λx.(x x)",
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"W = M M",
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"Y = λf.( (λx.(f (x x))) (λx.(f (x x))) )",
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"PAIR = λabi.( i a b )",
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"S = λnfa.(f (n f a))",
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"Z = λn.n (λa.F) T",
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"MULT = λnmf.n (m f)",
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"H = λp.((PAIR (p F)) (S (p F)))",
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"D = λn.n H (PAIR 0 0) T",
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"FAC = λyn.(Z n)(1)(MULT n (y (D n)))"
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])
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while True:
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try:
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i = r.prompt()
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@ -101,7 +101,14 @@ def cmd_load(command, runner):
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lines = [x.strip() for x in f.readlines()]
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for i in range(len(lines)):
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l = lines[i]
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l = lines[i].strip()
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# Skip comments and empty lines
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if l.startswith("#"):
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continue
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if l == "":
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continue
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try:
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x = runner.parse(l)[0]
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except ppx.ParseException as e:
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@ -56,7 +56,7 @@ class LambdaParser:
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(self.lp + self.pp_history + self.rp)
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)
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self.pp_command = pp.Suppress(":") + pp.Word(pp.alphas + "_") + pp.Word(pp.alphas + pp.nums + "_")[0, ...]
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self.pp_command = pp.Suppress(":") + pp.Word(pp.alphas + "_") + pp.Word(pp.alphas + pp.nums + "_.")[0, ...]
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self.pp_all = (
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@ -1,5 +1,7 @@
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from prompt_toolkit.styles import Style
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from prompt_toolkit.formatted_text import HTML
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from prompt_toolkit.lexers import Lexer
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from prompt_toolkit.key_binding import KeyBindings
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from prompt_toolkit import print_formatted_text as printf
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from importlib.metadata import version
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@ -14,6 +16,11 @@ style = Style.from_dict({ # type: ignore
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"code": "#AAAAAA italic",
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"muted": "#AAAAAA",
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# Syntax highlighting colors
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"syn_cmd": "#FFFFFF italic",
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"syn_lambda": "#AAAAAA",
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"syn_paren": "#AAAAAA",
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# Command formatting
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# cmd_h: section titles
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# cmd_key: keyboard keys, usually one character
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@ -28,6 +35,46 @@ style = Style.from_dict({ # type: ignore
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})
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# Replace "\" with pretty "λ"s
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bindings = KeyBindings()
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@bindings.add("\\")
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def _(event):
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event.current_buffer.insert_text("λ")
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# Simple lexer for highlighting.
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# Improve this later.
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class LambdaLexer(Lexer):
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def lex_document(self, document):
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def inner(line_no):
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out = []
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tmp_str = []
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d = str(document.lines[line_no])
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if d.startswith(":"):
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return [
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("class:syn_cmd", d)
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]
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for c in d:
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if c in "\\λ.":
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if len(tmp_str) != 0:
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out.append(("class:text", "".join(tmp_str)))
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out.append(("class:syn_lambda", c))
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tmp_str = []
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elif c in "()":
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if len(tmp_str) != 0:
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out.append(("class:text", "".join(tmp_str)))
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out.append(("class:syn_paren", c))
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tmp_str = []
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else:
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tmp_str.append(c)
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if len(tmp_str) != 0:
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out.append(("class:text", "".join(tmp_str)))
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return out
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return inner
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def show_greeting():
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# | _.._ _.|_
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# |_(_|| | ||_)
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@ -0,0 +1,77 @@
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# How to use exported files in lamb:
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#
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# [Syntax Highlighting]
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# Most languages' syntax highlighters will
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# highlight this code well. Set it manually
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# in your editor.
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#
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# Don't use a language for which you have a
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# linter installed, you'll get lots of errors.
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#
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# Choose a language you don't have extenstions for,
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# and a language that uses # comments.
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#
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# The following worked well in vscode:
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# - Julia
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# - Perl
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# - Coffeescript
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# - R
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# [Writing macros]
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# If you don't have a custom keyboard layout that can
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# create λs, you may use backslashes instead.
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# (As in `T = \ab.b`)
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#
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# This file must only contain macro definitons. Commands will be ignored.
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# Statements CANNOT be split among multiple lines.
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# Comments CANNOT be on the same line as macro defintions.
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# All leading whitespace is ignored.
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# Misc Combinators
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M = λx.(x x)
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W = (M M)
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Y = λf.((λx.(f (x x))) (λx.(f (x x))))
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# Booleans
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T = λab.a
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F = λab.b
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NOT = λa.(a F T)
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AND = λab.(a b F)
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OR = λab.(a T b)
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XOR = λab.((a (NOT b)) b)
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# Numbers
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# PAIR: prerequisite for H.
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# Makes a two-value tuple, indexed with T and F.
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#
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# H: shift-and-add, prerequisite for D
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#
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# S: successor (adds 1)
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#
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# D: predecessor (subtracts 1)
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#
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# Z: tests if a number is zero
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# NZ: equivalent to `NOT Z`
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#
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# ADD: adds two numbers
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#
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# MULT: multiply two numbers
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#
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# FAC:
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# Recursive factorial. Call with `Y FAC <number>`
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# Don't call this with numbers bigger than 5 unless you're very patient.
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#
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# `Y FAC 6` required 867,920 reductions and took 10 minutes to run.
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PAIR = λabi.(i a b)
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H = λp.((PAIR (p F)) (S (p F)))
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S = λnfa.(f (n f a))
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D = λn.((n H) ((PAIR 0) 0) T)
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Z = λn.(n (λa.F) T)
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NZ = λn.(n (λa.T) F)
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ADD = λmn.(m S n)
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MULT = λnmf.(n (m f))
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FAC = λyn.( (Z n)(1)((MULT n) (y (D n))) )
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@ -14,7 +14,7 @@ description = "A lambda calculus engine"
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#
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# Patch release:
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# Small, compatible fixes.
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version = "0.1.2"
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version = "0.1.3"
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dependencies = [
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"prompt-toolkit==3.0.31",
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