PRIMITIVES.md

• Primitives
  • Symbols
  • Special Forms
  • Core Primitives
  • Structure Methods
  • Standard Library
• Type Checking
• Testing
• See Also

Primitives

Here is a list of all the primitives which are available to yal users.

Note that you might need to consult the source of the standard-library, or the help file, to see further details. This document is primarily intended as a quick summary, and might lapse behind reality at times.

Symbols

The only notable special symbols are the following strings which represent the nil value. and our boolean values.

• nil
  • The nil value.
• #t
  • true is also available as an alias.
• #f
  • false is also available as an alias.

Characters are specified via the #\X syntax, for escaped characters you just need to add the escape:

• #\a -> "a"
• #\b -> "b"
• ..
• #\X -> "X"
• #\\n -> newline
• #\\t -> tab

Special Forms

Special forms are things that are built into the core interpreter, and include:

• alias
  • Define function aliases, this is used whenever we rename/change things in the standard-library to avoid breaking user scripts.
• catch.
  • Demonstrated in try.lisp.
• def!
  • define is an alias.
• defmacro!
  • Demonstrated in mtest.lisp.
• do
  • Execute each statement in the list.
• env
  • Env allows introspection of the current environment.
  • Demonstrated in dynamic.lisp
• eval
  • Execute the given expression.
• fn*
  • lambda is an alias.
• if
  • Our conditional operation.
• let*
  • Create a new scope, with locally bound variables.
• macroexpand
  • Expand the given macro.
• quote
  • Return the argument without evaluating it.
• read
  • Read a form from the specified string.
• set!
  • Set the value of a variable.
• struct
  • Define a structure.
• symbol
  • Create a new symbol from the given string.
• try
  • Error-catching warpper, demonstrated in try.lisp.

Core Primitives

Core primitives are those that can be overridden, and are implemented in golang, in the builtins/builtins.go file.

Things you'll find here include:

• #
  • Exponent function.
• %
  • Modulus function.
• *
  • Multiplication function.
• +
  • Addition function.
• -
  • Subtraction function.
• /
  • Division function.
  • Note that if only a single value is specified the reciprocal is returned - i.e. "(/ 3)" is equal to "1/3".
• /=
  • Numerical inequality test, if any argument is the same as another return false, otherwise if all arguments are unique return true.
• <
  • Less-than function.
• =
  • Numerical comparison function.
  • Note that multiple arguments are supported, not just two.
• arch
  • Return the operating system architecture.
• base
  • Convert the specified integer to a string, in the given base.
• car
  • Return the first item of a list.
• cdr
  • Return all items of the list, except the first.
• char=
  • Return true if the supplied values are characters, equal in value.
• char<
  • Return true if the first character is less than the second.
• char<=
  • Return true if the first character is less than, or equal to the second.
• char>
  • Return true if the first character is greater than the second.
• char>=
  • Return true if the first character is greater than, or equal to the second.
• chr
  • Return the ASCII character of the given number.
• cons
  • Add the element to the start of the given (potentialy empty) list.
• contains?
  • Does the specified hash contain the given key?
• date
  • Return details of today's date, as a list.
  • Demonstrated in time.lisp.
• dec2bin
  • Convert the specified integer to a binary string.
• dec2hex
  • Convert the specified integer to a hexadecimal string.
• directory?
  • Does the given path represent something that exists, and is a directory?
• directory:entries
  • Return all entries beneath a given directory, recursively.
• eq
  • Equality test, handling arbitrary types.
• error
  • Return an error.
• exists?
  • Does the given path exist?
• explode
  • Convert the supplied string to a list of characters.
• file?
  • Does the given path exist, and is it not a directory?
• file:lines
  • Return the contents of the given file, as a list of strings.
• file:read
  • Return the contents of the given file, as a string.
• file:stat
  • Return details of the given path.
• file:write
  • Write the specified content to the provided path.
• gensym
  • Generate, and return, a unique symbol. Useful for macro definitions.
• get
  • Get the given key from the specified hash.
• getenv
  • Read and return the given value from the environment.
• glob
  • Return the list of filenames matching the specified pattern.
• help
  • Return help for the specified function, either built-in or lisp.
• join
  • Convert every element of the supplied list into a string, and return the joined result.
• keys
  • Return the keys present in the specified hash.
  • Note that these are returned in sorted order.
• list
  • Create a new list.
• match
  • Perform a regular expression test.
• ms
  • Return the time, in milliseconds.
• nil?
  • Is the given value nil, or an empty list?
• nth
  • Return the nth element of the supplied list.
• now
  • Return the number of seconds past the Unix Epoch.
• number
  • Convert the specified string to a number. We accept base 2, 10, and 16.
  • Use the appropriate prefix in your input, for example "0b10101", or "0xFF".
• ord
  • Return the ASCII code of the specified character, or the first character of the supplied string.
• os
  • Return a string describing the current operating-system.
• pad:left
  • Pad the specified string to the given length, by prepending to it.
• pad:right
  • Pad the specified string to the given length, by appending to it.
• print
  • Output the specified string, or format string + values.
• set
  • Update the value of the specified hash-key.
• shell
  • Run a command via the shell, and return STDOUT and STDERR it generated.
• sort
  • Sort the given list.
• split
  • Split the given string, by the specified character.
• sprintf
  • Generate a string, using a format-string.
• str
  • Convert the specified parameter to a string.
• time
  • Return values relating to the current time, as a list.
  • Demonstrated in time.lisp.
• type
  • Return the type of the given object.
• vals
  • Return the values contained within the given hash.
  • Note that this returns things in the order of the sorted-keys.

Structure Methods

A structure is a minimal wrapper over a hash, but when a structure is defined several methods are created. Assuming a person-structure has been defined like so:

(struct person name age address)

There is now a new structure, named person with three fields name, age, and address which can be instantiated.

To help operate upon this structure several methods have also been created:

• (person "name" "age" "address")
  • Constructor method, which returns a new struct instance.
  • If the number of arguments is less than the number of object-fields they will be left unset (i.e. nil).
• (person? obj)
  • Returns true if the given object is an instance of the person struct.
• (person.name obj [new-value])
  • Accessor/Mutator for the name-field in the given struct instance.
• (person.age obj [new-value])
  • Accessor/Mutator for the age-field in the given struct instance.
• (person.address obj [new-value])
  • Accessor/Mutator for the address-field in the given struct instance.

Standard Library

The standard library consists of routines, and helpers, which are written in 100% yal itself.

The implementation of these primitives can be found in the following directory:

• stdlib/stdlib/

The code in those files is essentially prepended to any script that is supplied upon the command-line.

Functions here include:

• !
  • Logical "not".
• <=
  • Is the first number less than, or equal to, the second?
• >
  • Is the first number greater than the second?
• >=
  • Is the first number greater than, or equal to, the second?
• abs
  • Return the absolute value of the specified number.
• and
  • Logical operator, are all elements true?
• append
  • Append the given entry to the specified list.
• apply
  • Call the specified function on every element in the supplied list.
• apply-hash
  • Call the specified function against every key present in the specified hash.
• apply-pairs
  • Call the specified function on every two elements of the given list, as pairs.
• boolean?
  • Is the given thing a boolean?
• butlast
  • Return all elements of the supplied list, except for the last.
• concat
  • Join the specified lists.
• date:day
  • Return the current day of the month, via the output of date.
• date:month
  • Return the current month, via the output of date.
• date:weekday
  • Return the current day of the week, via the output of date.
• date:year
  • Return the current year, via the output of date.
• dec
  • Decrease the given thing by one.
• directory:walk
  • Invoke the specified callback, with every path-name contained beneath the specified directory - recursively.
• drop
  • Remove the specified number of elements from the provided list.
• error?
  • Is the given thing an error?
• even?
  • Is the given number even?
• every
  • Return true if applying the specified function to every element of the list returns a true result.
• file:stat:gid
  • Return the GID of the path, from the information provided by (file:stat).
• file:stat:mode
  • Return the mode of the path, from the information provided by (file:stat).
• file:stat:size
  • Return the size of the path, from the information provided by (file:stat).
• file:stat:uid
  • Return the UID of the path, from the information provided by (file:stat).
• file:which
  • Locate the specified binary's location, upon the users' PATH.
  • NOTE: This is almost certainly Unix/Linux/Darwin only, and will fail upon Windows systems.
• file:write
  • Write the specified content to the given path.
• filter
  • Remove every element from the given list, unless the function returns true.
• first
  • Return the first element of the given list.
  • This is the same as car.
• function?
  • Is the given thing a function?
• hash?
  • Is the given thing a hash?
• inc
  • Increment the given variable.
• intersection
  • Return those elements in common in the specified pair of lists.
• last
  • Return the last element of the specified list.
• length
  • Return the length of the specified list.
• list?
  • Is the given thing a list?
• lower
  • Return an lower-case version of the specified string.
• lower-table
  • A translation table for converting an upper-case character to lower-case.
• macro?
  • Is the given thing a macro?
• map
  • Return the results of applying the specified function to every element of the given list.
• map-pairs
  • Return the results of applying the specified function to every pair of elements in the given list.
• max
  • Return the maximum value in the specified list.
• member
  • Return true if the specified item is contained within the given list.
• min
  • Return the maximum value in the specified list.
• nat
  • Return the list of natural numbers 1 to N.
• neg
  • Negate the given number, and return it.
• neg?
  • Is the given number negative?
• nth
  • Return the Nth element of the list.
• number?
  • Is the given thing a number?
• odd?
  • Is the given number odd?
• one?
  • Is the given number equal to one?
• or
  • Logical operator, are any elements true?
• pos?
  • Is the given number positive?
• range
  • Return a list of numbers between the given start/end, using the specified step-size.
• reduce
  • Our reduce function, with the list, function and accumulator.
• repeat
  • Run the given body N times.
• repeated
  • Return a list of length N whose elements are all X.
• rest
  • Return the rest of the list, except the first element.
  • This is the same as cdr.
• reverse
  • Reverse the contents of the specified list.
• seq
  • Return a list of numbers from 0 to N.
• sign
  • Return the sign of the given number. (1 for positive, -1 for negative).
• sqrt
  • Return the square-root of the supplied number.
• string?
  • Is the given thing a string?
• strlen
  • Return the length of the specified string.
• substr
  • Return part of the specified string, identified by offset and length.
• symbol?
  • Is the given thing a symbol?
• take
  • Take only the first N items from the specified list.
• time:hms
  • Return the time in HH:MM:SS format, as a string.
• time:hour
  • Return the current hour, as found from (time).
• time:minute
  • Return the current minute, as found from (time).
• time:second
  • Return the current second, as found from (time).
• translate
  • Translate a string of characters, via a lookup table.
  • Used by lower, and upper.
• union
  • Return a list of all items in the specified two lists - without duplicates.
• upper
  • Return an upper-case version of the specified string.
• upper-table
  • A translation table for converting a lower-case character to upper-case.
• zero?
  • Is the given number zero?

Type Checking

Type checking is optional, but supported for function parameters via a :type suffix. Here's an example of type-checking on a parameter value, in this case a list is required, via the :list suffix:

(set! blah (fn* (a:list) (print "I received the list %s" a)))

(blah '(1 2 3))    ; => "I received the list (1 2 3)"
(blah #f)          ; => Error running: argument a to blah was supposed to be list, but got false
(blah 3)           ; => Error running: argument a to blah was supposed to be list, but got 3

The following type suffixes are permitted and match what you'd expect:

• :any
• :boolean
• :error
• :function
• :hash
• :list
• :nil
• :number
• :string
• :symbol

If multiple types are permitted then just keep appending things, for example:

• (set! blah (fn* (a:list:number) (print "I was given a list OR a number: %s" a)))
  • Allows either a list, or a number.

Testing

There is a simple set of tests written in Lisp, using a macro to define them easily, which can be viewed:

• lisp-tests.lisp

Adding new tests is easy enough that this file should be updated over time with new test-cases.

See Also

• LSP.md
  • LSP support.
• README.md
  • More details of the project.
• INTRODUCTION.md
  • Getting started setting variables, defining functions, etc.