SHEQ4

A tree-walking interpreter for SHEQ4, a higher-order functional language with lexical scoping. Written in C.

Documentation

See docs/ for full implementation details. Covers the C implementation, memory management, parsing, and evaluation with diagrams. Start with Overview.

Getting Started

Clone the repo, then create your .env file:

touch .env

Add your info:

UNIX_USER=your_calpoly_username
UNIX_HOST=unixN.csc.calpoly.edu
UNIX_PATH=path/to/your/project

Replace unixN with whichever server you use (unix1 through unix5). Set the path to wherever you want the project in your home directory.

Example:

UNIX_USER=krutledg
UNIX_HOST=unix3.csc.calpoly.edu
UNIX_PATH=csc_430/sheq4

Make the deploy script executable:

chmod +x deploy.sh

Create the directory on the unix server:

ssh your_username@unixN.csc.calpoly.edu "mkdir -p ~/path/to/your/project"

Deploying

./deploy.sh

This copies sheq4.c, Makefile, and test.sh to your unix server.

Building and Testing

SSH into the server and run:

cd ~/path/to/your/project
chmod +x test.sh
make
make test

Run a single expression:

./sheq4 '{+ 3 4}'

Language

SHEQ4 supports numbers, strings, booleans, conditionals, lambdas, and let bindings.

Primitives: +, -, *, /, <=, equal?, substring, strlen, error

Examples:

7                              => 7
"hello"                        => "hello"
{+ 3 4}                        => 7
{if true 1 2}                  => 1
{lambda (x) : {+ x 1}}         => #<procedure>
{{lambda (x) : {+ x 1}} 5}     => 6
{let {[x = 5]} in {+ x 3} end} => 8

Lambdas capture their environment at definition time:

{let {[add = {lambda (x) : {lambda (y) : {+ x y}}}]}
  in {{add 2} 3}
  end}
=> 5

Files

• sheq4.c — the interpreter
• test.sh — test suite
• Makefile — build configuration
• deploy.sh — pushes code to unix server
• .env — your local credentials (not tracked by git)
• docs/ — implementation documentation
• presentation/ — slides and figures for class presentation