107 lines
3.0 KiB
Markdown
107 lines
3.0 KiB
Markdown
# Lamb: A Lambda Calculus Engine
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## Installation
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### Method 1: PyPi (not yet)
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1. Put this on PyPi
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2. Write these instructions
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### Method 2: Git
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1. Clone this repository.
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2. Make and enter a [virtual environment](https://docs.python.org/3/library/venv.html).
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3. ``cd`` into this directory
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4. Run ``pip install .``
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5. Run ``python .``
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-------------------------------------------------
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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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```
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==> T = λab.a
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==> F = λab.a
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==> NOT = λa.a F T
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```
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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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Free variables will be shown with a `'`, like `a'`.
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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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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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You may use up/down arrows to recall history.
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Have fun!
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-------------------------------------------------
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## Commands
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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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`:clear` Clear the screen
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`:rlimit [int | None]` Set maximum reduction limit. `:rlimit none` sets no limit.
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`:macros` List macros in the current environment.
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`:mdel [macro]` Delete a macro
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`:step [yes | no]` Enable or disable step-by-step reduction. Toggle if no argument is given. When reducing by steps, the prompt tells you what kind of reduction was done last:
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- `M`: Macro expansion
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- `C`: Church expansion
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- `H`: History expansion
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- `F`: Function application
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`:expand [yes | no]` Enable or disable full expansion. Toggle if no argument is given. If full expansion is enabled, ALL macros will be expanded when printing output.
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`:delmac` Delete all macros
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`:save [filename]` \
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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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## Todo (pre-release, in this order):
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- Write "how it works"
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- PyPi package
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## Todo:
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- Prevent macro-chaining recursion
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- Cleanup warnings
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- Truncate long expressions in warnings
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- History indexing
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- Show history command
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- Loop detection
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- $\alpha$-equivalence check
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- Command-line options (load a file)
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- Unchurch command: make church numerals human-readable
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- Better Syntax highlighting
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- Complete file names and commands
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- Tests |