This is a minimalist lazy evaluation scheme interpreter implemented in C++. The main purpose of this project is educational.

It implements a subset of scheme specification, yet, is fully computational capable (i. e. it's Turing complete)

• (define <name> <expression>)
• (lambda (<formal parameter>+> <expression>)
• (cond (<condition> <expression>)+ )
• (if <condition> <consequent> <otherwise>)
• (quote <expression>)
• (include <file path>)

• integer, float (. for decimal), and negative numbers
• boolean values as #t and #f
• nil value
• symbols by using quotation

• (+ <number>+)
• (* <number>+)
• (/ <divident> <divisor>)
• (% <divident> <divisor>)
• (< <number> <number>)
• (> <number> <number>)
• (= <expression> <expression>)
• (display <expression>)
• (putchar <number>)
• (getchar)

• Uses great C++ STL library
• Mark and Sweep garbage collector
• Tail Call Optimization
• Lazy Evaluation
• interpreter mode (given command line file name)
• eval-print-loop mode

After compiling the project with make, the schemer executable can be used whether as an eval-print-loop or file interpreter (if given filename in command line):

./schemer [<.scm file>]

In eval-print-loop state (i. e. without parameter), the user can input line expressions and see it's evaluation. To exit the evaluator just hit Ctrl-D.

Errors normaly should not crash the interpreter. Rather, it should print the error message and continue to the next expression input line.

If a symbol needs to have a space, one can use double quotes (") to delimit such token (this can be useful for file path, that must consist of a single symbol), e. g.:

(include "examples/test 1.scm")

• Garbage Collector in interpreter mode
• Quotation syntax sugar (i. e. '(quoted expression))

• Scheme macros
• Compiling option
• Pure functional