Sketchy LISP

An Introduction to Functional Programming in Scheme

A.4 Scheme Syntax and Procedures

This is a summary of the Scheme syntax and procedures discussed in this book.

Key

body  a sequence of expressions
char  a char
expr  any type
form  any datum
int   an integer
list  a list
num   any numeric type
pair  a pair
proc  a procedure
procⁿ a procedure of n arguments
str   a string
sym   a symbol
tval  a truth value
void  an unspecific value
[x]   x is optional
x ... zero or more occurrences of x
x|y   x or y

Syntax

'form => form

Turn form into a datum. Alias: quote.

,expr => form

Evaluate expr in a quasiquote template. Alias: unquote.

,@expr => spliced-form

Evaluate expr in a quasiquote template and splice into surrounding list. Alias: unquote-splicing.

`qq-template => form

Quasiquote the quasiquote template qq-template. Alias: quasiquote.

(expr0 expr1 ...)

Apply expr₀ to expr₁... Expr₀ must reduce to a procedure.

(and expr1 ...) => form

Evaluate expressions in sequence until one gives #f.

(begin expr1 ...) => form

Evaluate expressions in sequence.

(case expr (list1 body1) (list2 body2) ...) => form

Evaluate first body whose list contains expr.

(cond (expr1 body1) (expr2 body2) ...) => form

Evaluate first body whose expr reduces to truth.

(define sym expr) => void

Introduce sym and bind it to (a location referring to) expr.

(define (sym1 sym2 ...) body) => void

(define (sym1 sym2 ... . symn) body) => void

Introduce sym₁ and bind it to (a location referring to) a procedure with the variables sym₂... and the given body.

(define-syntax keyword transformer) => void

Introduce the keyword keyword and bind it to the syntax transformer transformer. See also: syntax-rules.

(if expr1 expr2 [expr3]) => form

Evaluate to expr₂ if expr₁ reduces to truth, and to expr₃ otherwise.

(lambda sym body) => proc
(lambda (sym1 sym2 ... . symn) body) => proc

Evaluate to a variadic procedure with the variable sym (or the variables sym₁...) and the given body.

(lambda (sym1 ...) body) => proc

Evaluate to a procedure with the variables sym₁... and the given body.

(let ((sym1 expr1) ...) body) => form

Bind sym_i to expr_i locally giving a new context and evaluate body in that context.

(let* ((sym1 expr1) ...) body) => form

Like let, but bind expressions to symbols sequentially.

(letrec ((sym1 expr1) ...) body) => form

Like let, but fix recursive references.

(or expr1 ...) => form

Evaluate expressions in sequence until one gives truth.

(quasiquote qq-template) => form

Quasiquote the quasiquote template qq-template. Alias: `.

(quote form) => form

Turn form into a datum. Alias: '.

(set! sym expr) => void

Change the value of sym to expr.

(syntax-rules (sym1 ...) (pat1 temp1) (pat2 temp2) ...) => transformer

Evaluate to a syntax transformer. Sym₁... are local keywords, pat is a pattern and temp is a template. See also: define-syntax.

(unquote expr) => form

Evaluate expr in a quasiquote template. Alias: ,.

(unquote-splicing expr) => spliced-form

Evaluate expr in a quasiquote template and splice into surrounding list. Alias: ,@.

Procedures

(* num1 ...) => num

Evaluate to the product of the given numbers.

(+ num1 ...) => num

Evaluate to the sum of the given numbers.

(- num1 num2 ...) => num

Evaluate to the difference of the given numbers. If only one argument n is given, return -n.

(/ num1 num2 ...) => num

Evaluate to the quotient of the given numbers. If only one argument n is given, return 1/n.

(< num1 num2 num3 ...) => tval

(<= num1 num2 num3 ...) => tval

(> num1 num2 num3 ...) => tval

(>= num1 num2 num3 ...) => tval

Check whether the given arguments are in a specific order. E.g., < checks whether its arguments are in strict ascending order.

(= num1 num2 num3 ...) => tval

Check whether the given numbers are equivalent.

(abs num) => num

Return the absolute value of num.

(append list1 ...) => list

Append lists, giving a (proper) list.

(append list1 ... expr) => pair

Append lists, giving a (potentially improper) list.

(apply proc expr1 ... list) => form

Apply proc to the arguments in list. If exprs are given, cons them to list.

(assoc expr alist) => pair|#f

Find pair with key=expr in alist. Use equal? to compare keys.

(assq expr alist) => pair|#f

Find pair with key=expr in alist. Use eq? to compare keys.

(assv expr alist) => pair|#f

Find pair with key=expr in alist. Use eqv? to compare keys.

(caar pair) ... (cddddr pair) => form

Extract members of lists. E.g. (cadr x) = (car (cdr x)).

(call-with-current-continuation proc1) => form
(call/cc proc1) => form

Capture current continuation and pass it to proc¹.

(car pair) => form

Extract car part (head) of pair.

(cdr pair) => form

Extract cdr part (tail) of pair.

(char-ci<? char1 char2 char3 ...) => tval

(char-ci<=? char1 char2 char3 ...) => tval

(char-ci>? char1 char2 char3 ...) => tval

(char-ci>=? char1 char2 char3 ...) => tval

Check whether the given characters are in a specific lexical order. E.g., char-ci<? checks whether its arguments are in strict alphabetical order. Ignore the case of the characters.

(char-ci=? char1 char2 char3 ...) => tval

Check whether the given characters are equal. Ignore their case.

(char->integer char) => int

Convert char to integer.

(char-alphabetic? char) => tval

(char-lower-case? char) => tval

(char-numeric? char) => tval

(char-upper-case? char) => tval

(char-whitespace? char) => tval

Check properties of characters. E.g. (char-numeric? x) checks whether x is in the range #\0...#\9.

(char-downcase char) => char

(char-upcase char) => char

Change the case of a letter. E.g. (char-upcase #\c) => #\C.

(char<? char1 char2 char3 ...) => tval

(char<=? char1 char2 char3 ...) => tval

(char>? char1 char2 char3 ...) => tval

(char>=? char1 char2 char3 ...) => tval

Check whether the given characters are in a specific lexical order. E.g., char<? checks whether its arguments are in strict alphabetical order.

(char=? char1 char2 char3 ...) => tval

Check whether the given characters are equal.

(cons expr1 expr2) => pair

Construct a fresh pair with head=expr₁ and tail=expr₂.

(display expr [out-port]) => void

Print expr in a prettier but less accurate form than write. If an output port is specified, write to that port.

(eof-object? expr) => tval

Check whether expr is the end-of-file object.

(eq? expr1 expr2) => tval

Check whether expr₁ and expr₂ are identical.

(equal? expr1 expr2) => tval

Check whether expr₁ and expr₂ are equal.

(eqv? expr1 expr2) => tval

Check whether expr₁ and expr₂ are equivalent.

(floor num) => int

Return the greatest integer that is not greater than num.

(gcd int1 ...) => int

Return the greatest common divisor of int₁....

(integer->char int) => char

Convert integer to char.

(lcm int1 ...) => int

Return the least common multiple of int₁....

(length list) => int

Return the length of list.

(list expr1 ...) => list

Create a fresh list containing the given exprs and return it.

(list->string list) => str

Convert list to string.

(list-ref list int) => form

Extract the int'th member of list.

(list? expr) => tval

Check whether expr is a (proper) list.

(map proc list1 list2 ...) => list

Map procedure proc over the given lists.

(max num1 num2 ...) => num

Return the greatest of the given numbers.

(member expr list) => list|#f

Return the first sublist of list whose head equals expr, or #f if no such sublist exists. Use equal? to compare list elements.

(memq expr list) => list|#f

Return the first sublist of list whose head equals expr, or #f if no such sublist exists. Use eq? to compare list elements.

(memv expr list) => list|#f

Return the first sublist of list whose head equals expr, or #f if no such sublist exists. Use eqv? to compare list elements.

(min num1 num2 ...) => num

Return the least of the given numbers.

(modulo int1 int2) => int

Return int₁ modulo int₂ (division remainder).

(negative? num) => tval

Check whether num is negative.

(newline [out-port]) => void

Display a newline sequence. If an output port is given, write to that port.

(not expr) => tval

Logical not, i.e. (eq? expr #f).

(null? expr) => tval

Check whether expr is the empty list.

(number? expr) => tval

Check whether expr is a number.

(pair? expr) => tval

Check whether expr is a pair.

(quotient int1 int2) => int

Return the integer part of the quotient of int₁ and int₂.

(read [in-port]) => form

Read the external representation of a form and return a corresponding internal representation. If in input port is given, read from that port.

(read-char [in-port]) => char

Read a character and return it. If in input port is given, read from that port.

(remainder int1 int2) => int

Return the division remainder of int₁ and int₂.

(sqrt num) => num

Evaluate to the square root of num.

(string char1 ...) => str

Create a fresh string containing the given chars and return it.

(string->list str) => list

Convert string to list (of chars).

(string->symbol str) => sym

Convert string to symbol.

(string-ci<=? str1 str2 str3 ...) => tval

(string-ci<? str1 str2 str3 ...) => tval

(string-ci>=? str1 str2 str3 ...) => tval

(string-ci>? str1 str2 str3 ...) => tval

Check whether the given strings are in a specific lexical order. E.g., string-ci<? checks whether its arguments are in strict alphabetical order. Ignore case.

(string-ci=? str1 str2 str3 ...) => tval

Check whether the given strings are equal. Ignore case.

(string-length str) => int

Return the length of a string.

(string-ref str int) => char

Return int'th char of str.

(string<=? str1 str2 str3 ...) => tval

(string<? str1 str2 str3 ...) => tval

(string>=? str1 str2 str3 ...) => tval

(string>? str1 str2 str3 ...) => tval

Check whether the given strings are in a specific lexical order. E.g., string<? checks whether its arguments are in strict alphabetical order.

(string=? str1 str2 str3 ...) => tval

Check whether the given strings are equal.

(substring str int1 int2) => str

Extract substring starting at int₁ and extending up to but not including int₂ from str and return it.

(symbol->string sym) => str

Convert symbol to string.

(with-input-from-file str proc0) => form

Connect the standard input port to the file named in str and evaluate (proc⁰) in that context.

(with-output-to-file str proc0) => form

Connect the standard output port to the file named in str and evaluate (proc⁰) in that context.

(write expr [out-port]) => void

Write the external representation of expr. If an output port is specified, write to that port.

(zero? num) => tval

Check whether num equals zero.