_var'aq_ Specification
=================================

For better flavor text please read the [Original `var'aq` spec](https://www.oocities.org/connorbd/varaq/varaqspec.html) the following is a trimmed down version of the spec with a couple of fixes and addendums to how this implementation of the language works.

## 1 Language Overview

_var'aq_ is a stack-based, RPN programming language with points of similarity to Lisp, Forth, and PostScript. It is more of a functional language than an imperative (Algol-like) language; most operations are dependent on the stack and bypass the local variable store altogether.

### 1.2 Filetypes

*   `.vq -- application/varaq` -- a standard _var'aq_ source file
*   `.vqe -- application/varaq-engl` -- an English-keyword _var'aq_ source file

## 2 Language Basics

This section describes the fundamental _var'aq_ language constructs and data types.

### 2.1 Stack Operations

These operations directly manipulate the _var'aq_ operand stack. The operand stack can hold any of four kinds of data: numbers (real or integer), strings, functions, or arrays. It is best described as "translucent", similar to the transparent stack of Forth or PostScript but somewhat more restricted. The internal data representation of the stack is not available to the programmer.

#### 2.1.1 pop/woD

_obj `woD` -_

Pops and discards the top item on the stack. The literal meaning is _discard_.

Errors: stackUnderflow

#### 2.1.2 dup/latlh

_obj `latlh` obj obj_

Duplicates the top object on the stack.

Errors: stackUnderflow

#### 2.1.3 exch/tam

_obj1 obj2 `tam` obj2 obj1_

Inverts the order of the top two objects on the stack.

Errors: stackUnderflow

#### 2.1.4 clear/chImmoH

_... obj `chIm` -_

Empties the stack.

Errors: none

#### 2.1.5 remember/qaw

_\- `qaw` flag_

Puts a flag (like PostScript's `mark`) on the stack. The internal representation of the flag is not available to the programmer.

Errors: none

#### 2.1.6 forget/qawHa'

_... flag ... `qawHa'` ..._

Clears the stack down to the flag and pops the flag. If there is no flag present, the stack is emptied completely.

Errors: none

#### 2.1.7 dump/Hotlh (lit. scan)

_... `Hotlh` ..._

Prints the contents of the operand stack to STDOUT without changing them. _Note_: the _Hotlh_ operator is a debugging operator and is not intended for use in programs; it is merely documented here because it might be useful to a _var'aq_ developer. In particular, the output format of this operator is implementation-defined and will not be specified in this document. _Hotlh_ may be redefined to take such arguments as the implementor feels appropriate.

Errors: implementation-defined.

#### 2.1.8 disinter

Returns the value just above the top mark on the stack without disturbing the stack above it.

### 2.2 Data/Code Operations

_var'aq_, like many similar languages, does not distinguish between code and data. These operations include operators to associate names with objects and executable procedures, as well as operators to define and manage data structures. Note that variables and procedures live in a common namespace, since the act of pushing the content of a variable is essentially the same as executing the variable's name.

#### 2.2.1 ~ (quote/lI'moH)

_\- `~` obj obj_

The ~ operator is a special form, as it is not a postfix operator. When the interpreter encounters a ~, it pushes the next token on the stack as is regardless of whether it is a defined name. (Attempting to push an undefined name without a ~ will generate an undefinedName error.)

The literal meaning of this operator's name is "make useful". Errors: none

#### 2.2.2 {

Begins the creation of an anonymous procedure. The process is implementation-dependent.

#### 2.2.3 }

_\- `}` proc_

Completes procedure construction and pushes a reference to the completed procedure on the stack. Does not execute the procedure.

Errors: noDefinedProc

#### 2.2.4 name/pong

_obj id `pong` -_

Associates _obj_ with _id_ and places it in the system lookup space. Conventionally used to associate new operator names with procedure objects.

Example: _~ add3 { boq boq cha' } pong_

Pushes the name _add3_ and a procedure object on the stack, then binds the name to the procedure.

Errors: stackUnderflow, noDefinedProc

#### 2.2.5 set/cher

_obj id `cher` -_

Reassigns the value of a value already in the system lookup space. Used primarily for variable assignments.

Errors: stackUnderflow, noSuchName

#### 2.2.6 (\* ... \*) (comment)

Marks a comment in a program. All such comments are treated as single tokens and ignored.

#### 2.2.7 //_name_

Causes the interpreter to import a file with the name _name_.vq(e) and execute it as if it is part of the currently executing program. Essentially equivalent to `#include` in C.

An example can be found at the top of the [test.vqe](./examples/test.vqe) example.

`Note:` you must use either absolute paths or paths relitive to the location of the interpeter

### 2.3 Control Flow

_var'aq_ supports a small but sufficient supply of conditional and iterative operators.

#### 2.3.1 ifyes/HIja'chugh

_bool proc `HIja'chugh` -_

Pops the proc object off the stack, then evaluates the boolean. If it's true, the proc object is evaluated; otherwise, it's thrown out.

Errors: stackUnderflow, noDefinedProc

#### 2.3.2 ifno/ghobe'chugh

_bool proc `ghobe'chugh` -_

Similar to _HIja'chugh_ above, but executes proc only if bool is false.

Errors: stackUnderFlow, noDefinedProc

#### 2.3.3 choose/wIv

_bool `wIv` bool bool_

Duplicates a boolean value on top of the stack. Allows paired HI'ja'chugh/ghobe'chugh clauses.

`Note:` To the untrained eye, it may seem as though wIv and latlh are identical. This is true in the reference implementation, but may not be in any version that actually does some level of type checking. This bit of syntactic sugar should never be relied upon; always use wIv in this situation.

#### 2.3.4 eval/chov

_proc `chov` -_

Pops a proc object off the stack and executes it.

Errors: stackUnderflow, noDefinedProc

#### 2.3.5 escape/nargh

_bool `nargh` -_

Exit the current procedure. Useful for exit conditions on loops. Will terminate the current session if used top-level.

#### 2.3.6 repeat/vangqa'

_val proc `vangqa'` -_

Pops val and proc off the stack and executes proc val times.

### 2.4 List Operations

_var'aq_ supports a series of operators for management of lists (_ghomHom_, which seems to mean something like "cluster"). These primitives are the language's primary way of managing aggregate objects and work much like similar operators in LISP; a more sophisticated paradigm, such as OO extensions or the like, can be built with these operators.

Note that "objects" as they stand in _var'aq_ are largely singletons as in JavaScript; there is no inherent concept of object-orientation or anything like it in standard _var'aq_.

#### 2.4.1 (

Begins a list definition.

#### 2.4.2 )

_( item1 item2 ... `)` list_

Creates a list and pushes it onto the stack.

#### 2.4.3 split/SIj

_list `SIj` item1 list_

Pops a list off the stack and returns the first item and the rest of the list.

#### 2.4.4 cons/muv

_list item1 ... `muv` list_

Takes an object and adds it to the head of a list. Equivalent to the LISP `cons` operator.

#### 2.4.5 shatter/ghorqu'

_list `ghorqu'` item1 item2 ..._

Reduces a list to its component elements and pushes them on the stack in order.

`Note:` The precise meaning of the construction _ghorqu'_ is a bit obscure; the rendering _shatter_ is idiomatic and may derive from a nonstandard dialect. Standard Klingon would generally prefer _jor_, meaning _explode_.)

#### 2.4.6 empty?/chIm'a'

_list `chIm'a'` bool_

Examines a list on the stack and returns 1 if its value is null (_pagh_), a 0 if it contains anything.

#### 2.4.7 consume

_obj1 obj2 ... mark `consume` list_

Pops all objects on the stack down to _mark_ and returns them in a list.

`Note:` some implementations also have an operator known as bite/_chop_, equivalent to the Lisp _cdr_. This is not required in any standard _var'aq_ implementation and can easily be rendered by the function

```
~ chop { SIj woD } pong
```
    

### 2.5 String Operators  
_tlheghjangwI'mey_

#### 2.5.1 strtie/tlheghrar

_str1 str2 `tlheghrar` str3_

Concatenates the top two strings on the stack into one.

#### 2.5.2 compose/naQmoH

_mark str1 str2 ... strn `naQmoH` strn'_

Pops objects (executing proc objects if necessary) off the stack until a marker (placed by `qaw`) is hit and combines them into one string.

#### 2.5.3 streq?/tlheghrap'a'

_str1 str2 `tlheghrap'a'` bool_

Pops the top two strings on the stack, compares them, and returns 1 if identical, 0 if not.

#### 2.5.4 strcut/tlheghpe'

_str startval endval `tlheghpe'` substr_

Pops two values and a string and returns the section of the string between character _startval_ and character _endval_.

#### 2.5.5 strmeasure/tlheghjuv

_str `tlheghjuv` val_

Pops a string off the stack and returns its length in characters.

#### 2.5.6 explode/jor

_str `jor` list_

Separates individual "words" in a string by whitespace.

## 3 Mathematical Operators  
_mI'jangwI'mey_

### 3.1 Arithmetic Operations  
_toghwI'mey_

Arithmetic operators usually work with real numbers unless otherwise stated. The number operators (sec 3.3) can convert them to integers if necessary.

#### 3.1.1 add/boq

_a b `boq` sum_

Pops the top two values on the stack and replaces them with their sum.

#### 3.1.2 sub/boqHa'

_a b `boqHa'` difference_

Pops the top two values on the stack and replaces them with a - b.

#### 3.1.3 mul/boq'egh

_a b `boq'egh` product_

Pops the top two values on the stack and replaces them with their product.

#### 3.1.4 div/boqHa''egh

_a b `wav` quotient_

Pops the top two values on the stack and replaces them with a/b.

#### 3.1.5 idiv/HabboqHa''egh (lit. full-divide)

_a b `HabboqHa''egh` quotient_

Pops the top two values on the stack and replaces them with the results of an integer division operation.

#### 3.1.6 mod/chuv (lit. leftover)

_a b `chuv` remainder_

Pops the top two values and returns the remainder of a mod b.

#### 3.1.7 pow/boqHa'qa' (lit. remultiply)

_base exp `boqHa'qa'` real_

Pops the top two values and returns base^exp.

#### 3.1.8 sqrt/loS'ar (lit. fourth-howmuch)

_angle `loS'ar` real_

Returns the square root of val.

#### 3.1.9 add1/wa'boq

_a `wa'boq` a+1_

Increments the top value on the stack by one.

#### 3.1.10 sub1/wa'boqHa'

_a `wa'boqHa'` a-1_

Decrements the top value on the stack by one.

### 3.2 Trigonometric and Logarithmic Operators  
_SIHpojjangwI'mey 'ej ghurjangwI'mey_

#### 3.2.1 sin/yu'egh (lit. wave)

_angle `yu'egh` real_

Returns the sine of val.

#### 3.2.2 cos/yu'eghHa' (lit. counter-wave)

_angle `yu'eghHa'` cos(val)_

Returns the cosine of val.

#### 3.2.3 tan/qojmI' (lit. cliffnumber)

_angle `qojmI'` tan(val)_

Returns the tangent of val.

#### 3.2.4 atan/qojHa' (lit. anticliff)

_num den `qojHa'` angle_

Returns the arctangent of _num / den_.

#### 3.2.5 ln/ghurtaH

_num `ghurtaH` real_

Returns the natural log of _num_.

#### 3.2.6 log/maHghurtaH

_num `maHghurtaH` real_

Returns the base 10 log of _num_.

#### 3.2.7 log3/wejghurtaH

_num `wejghurtaH` real_

Returns the base 3 log of _num_.

### 3.3 Numerical Operators and Constants

This section describes operators that operate on numbers themselves, as well as common system-level constants. 

#### 3.3.1 clip/poD

_real `poD` int_

Removes the fractional portion of a real number (equivalent to floor(real).

#### 3.3.2 smooth/Hab (lit. smooth)

_real `Hab` int_

Rounds a number to the nearest integer.

#### 3.3.3 howmuch/'ar

_num `'ar` num2_

Returns the absolute value of _num_.

#### 3.3.4 setrand/mIScher

_num `mIScher` -_

Sets the random number generator seed value to _num_. Not common, since most _var'aq_ implementations have a rather arcane formula for picking a pseudo-random seed value.

#### 3.3.5 rand/mIS

_num `mIS` real_

Returns a random real number in the range 0 to _num_. If there is no meaningful input on the stack,

#### 3.3.6 pi/HeHmI'

Pushes the value pi (~3.14159...) onto the stack. The Klingon name literally means "edge-number".

#### 3.3.7 e/ghurmI'

Pushes the value e onto the stack. The Klingon name literally means "growth-number".

#### 3.3.8 int?/HabmI''a'

_val `HabmI''a'` bool_ Pops the top value on the stack and returns 1 if it is an integer, 0 if not.

#### 3.3.9 number?/mI''a'

_val `mI''a'` bool_

Pops the top value off the stack and returns 1 if it's a number, 0 if it's something else.

#### 3.3.10 numberize/mI'moH

_str `mi'moH` val_

Pops a string off the stack, converts it into a numerical value, and returns it.

#### 3.4 Bitwise operators

Though _var'aq_ makes no clear distinction between integers and reals, it is nevertheless useful to be able to manipulate a number on the bit level. The following operators assume that their operands will always be treated as integers; effects on floating-point values are undefined, and may be disallowed at the implementor's discretion.

#### 3.4.1 isolate/mobmoH

_a b `mobmoH` result_

Performs a bitwise AND on a and b.

#### 3.4.2 mix/DuD

_a b `DuD` result_

Performs a bitwise OR on a and b.

#### 3.4.3 contradict/tlhoch

_a b `tlhoch` result_

Performs a bitwise XOR on a and b.

#### 3.4.4 compl/Qo'moH

_val `Qo'moH` ~val_

Returns the one's-complement of val. `Note:` The literal meaning is something like "make it say no".

#### 3.4.5 shiftright/nIHghoS

_a b `nIHghoS` result_

Shifts a right b places, preserving the sign of the value.

#### 3.4.6 shiftleft/poSghoS

_a b `poSghoS` result_

Shifts a left b places.

### 4 Relational and Logical Operators

#### 4.1 Relational Operators and Predicate Functions  
_yu'jangwI'mey_

#### 4.1.1 gt?/law''a'

_a b `law''a'` bool_

Pops a and b off the stack, compares them, and returns a boolean value of true if a is larger.

#### 4.1.2 lt?/puS'a'

_a b `puS'a'` bool_

Pops a and b off the stack, compares them, and returns a boolean value of true if a is smaller.

#### 4.1.3 eq?/rap'a'

_a b `rap'a'` bool_

Pops a and b off the stack, compares them, and returns a boolean value of true if a is the same as b.

#### 4.1.4 ge?/law'rap'a'

_a b `law'rap'a'` bool_

Pops a and b off the stack, compares them, and returns a boolean value of true if a is greater than or equal to b.

#### 4.1.5 le?/puSrap'a'

_a b `puSrap'a'` bool_

Pops a and b off the stack, compares them, and returns a boolean value of true if a is less than or equal to b.

#### 4.1.6 ne?/rapbe'a'

_a b `rapbe'a'` bool_

Pops a and b off the stack, compares them, and returns a boolean value of true if a is not equal to b.

#### 4.1.7 null?/pagh'a'

_obj `pagh'a'` bool_

Examines the top object on the stack and returns a 1 if null, a 0 if not.

#### 4.1.8 negative?/taH'a'

_val `taH'a'` bool_

Pops the top number on the stack and returns a 1 if less than 0, a 0 if not.

#### 4.2 Logical Operators  
_vItjangwI'mey_

Note that these are strictly logical operators, not bitwise.

#### 4.2.1 and/je

_a b `je` bool_

Evaluates b and a and returns a 1 if both are true, a 0 if not.

#### 4.2.2 or/joq

_a b `joq` bool_

Evaluates b and a and returns a 1 if one or both are true, a 0 if both are false.

#### 4.2.3 xor/ghap

_a b `ghap` bool_

Evaluates b and a and returns a 1 if only one is true, a 0 otherwise.

#### 4.2.4 not/ghobe'

_val `ghobe'` bool_

Evaluates val and returns 1 if true, 0 if not.

### 5 Input/Output and File Operators

The _var'aq_ Level 0 specification essentially handles console I/O and files in a manner very similar to the UNIX model.

#### 5.1 Console I/O

The console I/O model at this point is very simple: write, read, error.

#### 5.1.1 disp/cha'

_obj `cha'` -_

Pops the top object on the stack and writes it to STDOUT. Note that certain types of objects will generate meaningless output, particularly anonymous proc objects.

#### 5.1.2 listen/'Ij

_\- `'Ij` str_

Reads one line of input and stores it as a string on top of the stack.

#### 5.1.3 complain/bep

_str `bep` -_

Pops _str_ and prints it to stderr.

### 6 System Variables  
_patSarwI'mey_

This section describes _var'aq_ keywords that do no more than put set values on the stack. Many of them are not precisely constants but more like environment variables.

#### 6.1 I/O-related Constants

#### 6.1.1 newline/chu'DonwI'

_- `chu'DonwI'` '\n'_

Prints a carriage return.

#### 6.1.2 tab/chu'tut

_- `chu'DonwI'` '\t'_

Advances by one tab stop.

#### 6.2 Environment Constants

#### 6.2.1 whereami/nuqDaq\_jIH

_- `nuqDaq_jIH` "string of your local ip address"_

Returns the IP address of the machine the interpreter is running on.

#### 6.2.2 version/pongmI'

_- `pongmI'` "string of version"_

Returns the current interpreter version number. The reference interpreter returns a date stamp.

#### 6.2.3 argv/taghDe'

_- `taghDe'` (arg1, arg2, ...)_

Pushes the command line arguments on the stack as a list.

## 7 New Operators

The following are all new operators that are not included in the original perl implementation of _var'aq_

### 7.1 Stack Operations

These are stolen directly from _Forth_ (specifically the [_FORTH-79 Handy Reference_](http://www.forth.org/Ting/Forth-for-the-Complete-Idiot/Forth-79-Handy-Reference.pdf) from the book _Forth for the Complete Idiot_), 

They are very useful for doing operations without clobbering the stack

#### 7.1.1 over/QI

_obj1 obj2 `QI` obj1 obj2 obj1_

Make a copy of the second item on top of the stack.

The direct Klingon translation for `QI` is bridge, as in a bridge over a river, which works close enough.

Errors: stackUnderflow
#### 7.1.2 pick/woH

_N `woH` objN_

Make a copy of the Nth item on top of the stack.

For example _1 `woH`_ is the same as `latlh` & _2 `woH`_ is the same as `QI`

Errors: stackUnderflow, stackOverflow

#### 7.1.3 rot/jIr

_obj1 obj2 obj3 `jIr` obj2 obj3 obj1_

Rotate the third item to the top of the stack.

Errors: stackUnderflow

#### 7.1.4 depth/juv

_- `juv` num_

Count the number of items on the stack and push that number to the top of the stack.

Errors: stackUnderflow