Introduction to Scheme - Revision history

Carli: /* Deeper Topics into Scheme */

2025-08-25T16:02:59Z

Deeper Topics into Scheme

Carli: /* Deeper Topics into Scheme */

2024-05-17T14:26:17Z

Deeper Topics into Scheme

← Older revision		Revision as of 16:26, 17 May 2024
Line 79:		Line 79:
	You can deep-dive into the following topcis:		You can deep-dive into the following topcis:

	* Lists and Objects		* [[Lists and Objects]]
	* Pattern Matching		* [[Pattern Matching]]
	* Parsers		* [[Parsers]]

	== Further Help and Documentation of all Functions ==		== Further Help and Documentation of all Functions ==

Carli at 14:25, 17 May 2024

2024-05-17T14:25:57Z

@@ Line 76: / Line 76: @@
 Lambda functions can be passed to other functions as values. They enclose your original scope, so you can use variables from the outside inside your function.
-== List handling ==
+== Deeper Topics into Scheme ==
-The following list functions can be used:
+You can deep-dive into the following topcis:
-== Associative Lists (Objects) ==
+* Lists and Objects
-The following functions can be used:
+* Pattern Matching
- > (set obj '("a" 1 "b" 2 "c" 3)) /* construct object from a list with alternating key-value */
+* Parsers
 == Further Help and Documentation of all Functions ==

Carli at 14:24, 17 May 2024

2024-05-17T14:24:16Z

@@ Line 29: / Line 29: @@
   > 12
   = 12
   > "hi"
   = "hi"
   > (+ 1 2)
   = 3
   > (+ 1 2 3)
   = 6
   > (+ 2 (* 2 2))
   = 6
   > (+ 2 (* 2 4))
   = 10
   > (concat "Hello" "World")
   = "HelloWorld"
@@ Line 69: / Line 75: @@
   = 4
 Lambda functions can be passed to other functions as values. They enclose your original scope, so you can use variables from the outside inside your function.
 == Further Help and Documentation of all Functions ==

Carli: Created page with "When you run `./memcp`, you will be dropped at a scheme shell like this: memcp Copyright (C) 2023, 2024 Carl-Philip Hänsch This program comes with ABSOLUTELY NO WARRANTY; This is free software, and you are welcome to redistribute it under certain conditions; loading storage /tmp/x/system/bdf64a22-6315-463c-bbf7-329317ad50ed-id of type 10 loading storage /tmp/x/system/bdf64a22-6315-463c-bbf7-329317ad50ed-username of type 20 loading stora..."

2024-05-17T13:36:30Z

Created page with "When you run <code>./memcp</code>, you will be dropped at a scheme shell like this: memcp Copyright (C) 2023, 2024 Carl-Philip Hänsch This program comes with ABSOLUTELY NO WARRANTY; This is free software, and you are welcome to redistribute it under certain conditions; loading storage /tmp/x/system/bdf64a22-6315-463c-bbf7-329317ad50ed-id of type 10 loading storage /tmp/x/system/bdf64a22-6315-463c-bbf7-329317ad50ed-username of type 20 loading stora..."

New page

When you run <code>./memcp</code>, you will be dropped at a scheme shell like this:
memcp Copyright (C) 2023, 2024 Carl-Philip Hänsch
This program comes with ABSOLUTELY NO WARRANTY;
This is free software, and you are welcome to redistribute it
under certain conditions;

loading storage /tmp/x/system/bdf64a22-6315-463c-bbf7-329317ad50ed-id of type 10
loading storage /tmp/x/system/bdf64a22-6315-463c-bbf7-329317ad50ed-username of type 20
loading storage /tmp/x/system/bdf64a22-6315-463c-bbf7-329317ad50ed-password of type 20

Welcome to memcp

performing unit tests ...
finished unit tests
test result: 15/15
all tests succeeded.

Initializing SQL frontend
MySQL server listening on port 3307 (connect with `mysql -P 3307 -u root -p` using password 'admin')
listening on <nowiki>http://localhost:4321</nowiki>

Type (help) to show help

>
Scheme is a functional programming language and a subset of LISP. Every expression is either a primitive value or a list.

To understand the semantics of Scheme, take a look at the following Scheme REPL session:
> 12
= 12
> "hi"
= "hi"
> (+ 1 2)
= 3
> (+ 1 2 3)
= 6
> (+ 2 (* 2 2))
= 6
> (+ 2 (* 2 4))
= 10
> (concat "Hello" "World")
= "HelloWorld"

== Syntax ==

=== Function Call ===
A function call has the following format:
(functionname param1 param2 param3 ...)
Function calls start with <code>(</code>, contain one function and zero or more parameters separated by space .

Some basic functions are <code>+ - * / print concat</code>. For more consult the manual with <code>(help)</code>.

=== Literals ===
The following literals are allowed:

* Number Literals: <code>1 2 3 56 7.5 4.3e20 -6.123e-3</code>
* String Literals: <code>"Hello World" "First Line\nSecond Line" "he said: \"what?\" and smiled"</code>
* Function names: <code>print</code>
* Symbol literals <code>'print</code>
* List literals <code>'(1 2 3) '("a" "b" "c")</code>
* Associative Array literals <code>'("key" "value" "size" 45 "name" "Peter" "sublist" '(1 2 3))</code> - associative arrays are lists with key value pairs flattened down to a one dimensional list of an even number of items.
* Lambdas: <code>(lambda (param1 param2 ...) body)</code>

=== Lambda Functions ===
Scheme allows for creating lambda functions which enclose their own scope:
(define decrease-by-one (lambda (number) (- number 1)))
The function can now be called from scheme:
> (decrease-by-one 5)
= 4
Lambda functions can be passed to other functions as values. They enclose your original scope, so you can use variables from the outside inside your function.

== Further Help and Documentation of all Functions ==
If you type <code>(help)</code> into the console, you will get the following overview:
> (help)
Available scm functions:

-- SCM Builtins --
quote: returns a symbol or list without evaluating it
eval: executes the given scheme program in the current environment
optimize: optimize the given scheme program
if: checks a condition and then conditionally evaluates code branches; there might be multiple condition+true-branch clauses
and: returns true if all conditions evaluate to true
or: returns true if at least one condition evaluates to true
coalesce: returns the first value that has a non-zero value
coalesceNil: returns the first value that has a non-nil value
define: defines or sets a variable in the current environment
set: defines or sets a variable in the current environment
error: halts the whole execution thread and throws an error message
try: tries to execute a function and returns its result. In case of a failure, the error is fed to the second function and its result value will be used
apply: runs the function with its arguments
apply_assoc: runs the function with its arguments but arguments is a assoc list
symbol: returns a symbol built from that string
list: returns a list containing the parameters as alements
string: converts the given value into string
match: takes a value evaluates the branch that first matches the given pattern
lambda: returns a function (func) constructed from the given code
begin: creates a own variable scope, evaluates all sub expressions and returns the result of the last one
parallel: executes all parameters in parallel and returns nil if they are finished
source: annotates the node with filename and line information for better backtraces

-- Arithmetic / Logic --
number?: tells if the value is a number
+: adds two or more numbers
-: subtracts two or more numbers from the first one
*: multiplies two or more numbers
/: divides two or more numbers from the first one
<=: compares two numbers
<: compares two numbers
>: compares two numbers
>=: compares two numbers
equal?: deep-compares two values of the same type
equal??: performs a sloppy equality check on primitive values (number, string, bool. nil), strings are compared case insensitive
!: negates the boolean value
not: negates the boolean value
nil?: returns true if value is nil
min: returns the smallest value
max: returns the highest value
floor: rounds the number down
ceil: rounds the number up
round: rounds the number

-- Strings --
string?: tells if the value is a string
concat: concatenates stringable values and returns a string
substr: returns a substring
simplify: turns a stringable input value in the easiest-most value (e.g. turn strings into numbers if they are numeric
strlen: returns the length of a string
strlike: matches the string against a wildcard pattern (SQL compliant)
toLower: turns a string into lower case
toUpper: turns a string into upper case
replace: replaces all occurances in a string with another string
split: splits a string using a separator or space
htmlentities: escapes the string for use in HTML
urlencode: encodes a string according to URI coding schema
urldecode: decodes a string according to URI coding schema

-- Lists --
append: appends items to a list and return the extended list.
append_unique: appends items to a list but only if they are new.
cons: constructs a list from a head and a tail list
car: extracts the head of a list
cdr: extracts the tail of a list
merge: flattens a list of lists into a list containing all the subitems. If one parameter is given, it is a list of lists that is flattened. If multiple parameters are given, they are treated as lists that will be merged into one
merge_unique: flattens a list of lists into a list containing all the subitems. Duplicates are filtered out.
has?: checks if a list has a certain item (equal?)
filter: returns a list that only contains elements that pass the filter function
map: returns a list that contains the results of a map function that is applied to the list
mapIndex: returns a list that contains the results of a map function that is applied to the list
reduce: returns a list that contains the result of a map function
produce: returns a list that contains produced items - it works like for(state = startstate, condition(state), state = iterator(state)) {yield state}
produceN: returns a list with numbers from 0..n-1
list?: checks if a value is a list
contains?: checks if a value is in a list; uses the equal?? operator

-- Associative Lists / Dictionaries --
filter_assoc: returns a filtered dictionary according to a filter function
map_assoc: returns a mapped dictionary according to a map function
reduce_assoc: reduces a dictionary according to a reduce function
has_assoc?: checks if a dictionary has a key present
extract_assoc: applies a function (key value) on the dictionary and returns the results as a flat list
set_assoc: returns a dictionary where a single value has been changed.
merge_assoc: returns a dictionary where all keys from dict1 and all keys from dict2 are present.

-- Parsers --
parser: creates a parser

-- Sync --
newsession: Creates a new session which is a threadsafe key-value store represented as a function that can be either called as a getter (session key) or setter (session key value) or list all keys with (session)
once: Creates a function wrapper that you can call multiple times but only gets executed once. The result value is cached and returned on a second call. You can add parameters to that resulting function that will be passed to the first run of the wrapped function.
mutex: Creates a mutex. The return value is a function that takes one parameter which is a parameterless function. The mutex is guaranteed that all calls to that mutex get serialized.

-- IO --
print: Prints values to stdout (only in IO environment)
help: Lists all functions or print help for a specific function
import: Imports a file .scm file into current namespace
load: Loads a file and returns the string
serve: Opens a HTTP server at a given port
mysql: Imports a file .scm file into current namespace
password: Hashes a password with sha1 (for mysql user authentication)

-- Storage --
[[scan]]: does an unordered parallel filter-map-reduce pass on a single table and returns the reduced result
[[Scan|scan_order]]: does an ordered parallel filter and serial map-reduce pass on a single table and returns the reduced result
createdatabase: creates a new database
dropdatabase: creates a new database
createtable: creates a new database
createcolumn: creates a new column in table
shardcolumn: tells us how it would partition a column according to their values. Returns a list of pivot elements.
altertable: alters a table
droptable: removes a table
insert: inserts a new dataset into table
stat: return memory statistics
show: show databases/tables/columns
rebuild: rebuilds all main storages and returns the amount of time it took
loadCSV: loads a CSV file into a table and returns the amount of time it took.
loadJSON: loads a .jsonl file from disk into a database and returns the amount of time it took.
settings: reads or writes a global settings value. This modifies your data/settings.json.

get further information by typing (help "functionname") to get more info