A handcrafted scheme interpreter, with lexical scoping, closures, tail recursion, and delayed evaluation enabling use of streams, as in sample programs

Lexical Grammar:

reduced version of https://schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-10.html#%_sec_7.1.1

token -> keyword | identifier | number | string | boolean | character | ( | ) | .
comment -> ; all characters until line break
keyword -> else | define | quote | lambda | if | set! | begin | cond | and | or | case | let | let* | letrec | delay
identifier -> initial subsequent* | peculiaridentifier
initial -> alpha | ! | $ | % | & | * | / | : | < | = | > | ? | ^ | _ | ~
subsequent -> initial | digit | + | - | .
peculiaridentifier -> + | -
number -> sign? (digit*.digit+ | digit+.digit*)
string -> "any character except "*"
character -> #\any character | #\newline | #\space
boolean -> #t | #f
alpha -> a | b | ... | Z
digit -> 0 | 1 | ... | 9

see also:
https://www.scheme.com/tspl2d/grammar.html
https://www.scheme.com/tspl4/grammar.html
https://docs.microsoft.com/en-us/cpp/c-language/lexical-grammar?view=msvc-160

Syntax Grammar:

Subset of https://schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-10.html#%_sec_7.1.3

program -> (expression | definition)*
definition -> (define identifier expression) | (define (identifier defformals) body)
defformals -> identifier*
expression -> identifier | literal | call | lambda | conditional | assignment
literal -> quotation | self-evaluating
self-evaluating -> boolean | character | number | string
quotation -> 'datum | (quote datum)
datum -> boolean | character | number | string | identifier | list
list -> (datum*)
call -> (operator operand*)
operator -> expression
operand -> expression
lambda -> ("lambda" formals body)
formals -> identifier | (identifier*)
body -> defintion* expression+
conditional -> ("if" test consequent alternate?)
test -> expression
consequent -> expression
alternate -> expression
assignment -> (set! identifier expression)

in addition to derived expressions: cond, and, or, let, let*, letrec, begin, delay
for a list of derived expressions: https://schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-7.html#%_chap_4

see also:
https://schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-10.html#%_sec_7.1.3
https://schemers.org/Documents/Standards/R5RS/HTML/ chapters 4 & 5

Standard Procedures:

• Equivalence Predicates:
  • eqv?
  • eq?
  • equal?
• Number Operation:
  • number?
  • integer?
  • <
  • <=
  • >
  • >=
  • =
  • +
  • -
  • /
  • *
  • zero?
  • positive?
  • negative?
  • odd?
  • even?
  • max
  • min
  • abs
  • remainder
• Booleans:
  • not
  • boolean?
• Pairs and Lists:
  • pair?
  • cons
  • car
  • cdr
  • set-car!
  • set-cdr!
  • caar ... cddddr
  • null?
  • list?
  • list
  • length
  • append
• Control Features
  • procedure?
  • apply
  • map
  • for-each
  • force
  • make-promise
• Eval

for a complete list of possible procedures: https://schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-9.html#%_chap_6