https://github.com/rbaron/scam

A toy Lisp interpreter in C
https://github.com/rbaron/scam

Last synced: about 2 months ago
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A toy Lisp interpreter in C

• Host: GitHub
• URL: https://github.com/rbaron/scam
• Owner: rbaron
• Created: 2016-09-28T22:36:55.000Z (over 8 years ago)
• Default Branch: master
• Last Pushed: 2016-09-30T22:29:21.000Z (over 8 years ago)
• Last Synced: 2024-04-24T16:14:52.890Z (9 months ago)
• Language: C
• Homepage:
• Size: 14.6 KB
• Stars: 1
• Watchers: 3
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

Awesome Lists containing this project

• AwesomeInterpreter - scam

README

        
# scam

scam is a toy/minimalistic Lisp interpreter written in C.

## Status

Lacking critical features:

- Garbage collection;

- String manipulation primitives;

- Tail recursion optimization;

## Compiling

```bash

$ make

```

## Examples

Code is read from stdin. The `examples.scam` file is interpretable. You can run it with `cat examples.scam | ./scam`. Here it is:

```lisp

;

; Types

;

; Numeric

42

; => NUMBER 42.000000

; String

"Hello, world"

; => STRING Hello, world

; Boolean

true

; => BOOLEAN 1

false

; => BOOLEAN 0

;

; Numeric primitive operators

;

(+ 1 2)

; => NUMBER 3.000000

(* 2 (- 1 2) (/ 2 2))

; => NUMBER -2.000000

;

; Numeric primitive predicates

;

(== 1 2)

; => BOOLEAN 0

(> 2 1)

; => BOOLEAN 1

(< 1 2)

; => BOOLEAN 0

;

; User defined procedures

;

(define factorial (lambda (n)

  (if (== n 1)

    1

    (* n (factorial (- n 1))))))

; => USER DEFINED PROCEDURE WITH ARGS n,

;

; I/O

;

(display "6! = " (factorial 6))

; 6! = 720.000000

; => BOOLEAN 1

(display "This is a number: " 1 " and this is another: " 2)

; This is a number: 1.000000 and this is another: 2.000000

; => BOOLEAN 1

```

## Debugging

You can add a `--debug` switch to add debug information to the output. E.g.:

- `fib.scam` - Evaluates the 8th Fibonacci number

```

$ cat fib.scam | ./scam

=> NUMBER 21.000000

```

```

$ cat fib.scam | ./scam --debug

TOKENS (45)

==========

(, begin, (, define, fib, (, lambda, (, n, ), (, if, (, <, n, 3, ), 1, (, +, (, fib, (, -, n, 1, ), ), (, fib, (, -, n, 2, ), ), ), ), ), ), (, fib, 8, ), ),

AST:

====

COMPOUND

    SYMBOL begin

    COMPOUND

        SYMBOL define

        SYMBOL fib

        COMPOUND

            SYMBOL lambda

            COMPOUND

                SYMBOL n

            COMPOUND

                SYMBOL if

                COMPOUND

                    SYMBOL <

                    SYMBOL n

                    NUMBER 3.000000

                NUMBER 1.000000

                COMPOUND

                    SYMBOL +

                    COMPOUND

                        SYMBOL fib

                        COMPOUND

                            SYMBOL -

                            SYMBOL n

                            NUMBER 1.000000

                    COMPOUND

                        SYMBOL fib

                        COMPOUND

                            SYMBOL -

                            SYMBOL n

                            NUMBER 2.000000

    COMPOUND

        SYMBOL fib

        NUMBER 8.000000

ENV:

====

fib => USER DEFINED PROCEDURE WITH ARGS n,

< => PRIMITIVE PROCEDURE

> => PRIMITIVE PROCEDURE

== => PRIMITIVE PROCEDURE

/ => PRIMITIVE PROCEDURE

* => PRIMITIVE PROCEDURE

- => PRIMITIVE PROCEDURE

+ => PRIMITIVE PROCEDURE

true => BOOLEAN 1

false => BOOLEAN 0

RESULT:

=======

=> NUMBER 21.000000

```