92 lines
3.8 KiB
Markdown
92 lines
3.8 KiB
Markdown
# Tigersay
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## The dOvs Course ##
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This last semester I've been following my university's course on
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writing a compiler from scratch. The course uses the classic
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[Modern Compiler Implementation in
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ML](https://www.cs.princeton.edu/%7Eappel/modern/ml/), and thus our
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input language is something called **Tiger**, a toy language designed
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specifically for the book. The joke goes that Tiger is one of the
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least used programming languages, but one of the most supported. It is
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also weird. It's like if **C** and [Standard
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ML](https://en.wikipedia.org/wiki/Standard_ML) had a deformed baby:
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Mutually inductive data types and functions? Sure! Primitives for both
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functional and imperative coding styles? Great idea! Type inference
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for variables, but not for functions. Perfect! A way to determine the
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size of arrays at runtime? No, absolutely not!
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The reason for these weird idiosyncrasies is obvious: nobody is
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supposed to write actual programs in Tiger. The features of
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Tiger are designed to illustrate how to implement them, not
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necessarily to form a coherent whole.
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That said, some of the features work together to allow a strange
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elegance in the way some programs can be written. Recursive functions
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and structure types allow one to express linked lists and maps using
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relatively little code. See [the example
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code](https://gitfub.space/Jmaa/tigersay/src/branch/master/tiger-linked-list.tig)
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above, for an implementation of a linked list, and a function for finding the sum of
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the list, using a recursive helper function. I could just as easily
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have implemented it using an imperative style.
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<!-- TODO: Include link to tests. -->
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While following the course, my group used a testing framework,
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containing many programs similar in style to the above code sniplet,
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ensuring our compiler's compliance with the language. These
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tests were small, and rarely tested more than a few features at once.
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The question "Is our compiler actually capable of translating a _real_
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program?" arose, and this lead me down the road of actually writing a
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"real" program in Tiger, using its weird feature set.
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## Tigersay ##
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<!--start-->
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**Tigersay** is an implementation of the classic Perl program
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[Cowsay](https://en.wikipedia.org/wiki/Cowsay), written in the Tiger
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programming language, a toy language originating from the [Modern
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Compiler Implementation in
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ML/C/Java](https://www.cs.princeton.edu/%7Eappel/modern/ml/) series of
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books.
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It does not come compiled, nor does it come with a **Tiger** compiler.
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The only way to experience the wonder that is **Tigersay** is to use
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your own **Tiger** compiler. (Or find one on the internet, but that's
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cheating.)
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<!--end-->
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The standard version of Tiger is limited in its ability to interact
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with the command-line, and as a result, so is Tigersay. The only way
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to interact with Tigersay is to pipe the desired text into Tigersay:
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```bash
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echo "Hello World" | tigersay
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```
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Unfortunately this also means Tigersay only supports a single face,
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the default tiger one, due to having no support for command-line
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arguments.
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Tigersay responds to certain strings in silly ways, the most useful
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ones being _help_ and _version_. Additionally it interfaces nicely
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with [fortune](https://en.wikipedia.org/wiki/Fortune_(Unix\)).
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If you'd like to play around with Tigersay yourself, you can find the source
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code in the [Gitfub repository](https://gitfub.space/Jmaa/tigersay)
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