Chimera Language Spec

This document contains the technical specification of the Chimera programming language.

Lexical Elements
Syntax
Semantics
API Specification
Source Code Examples

Lexical Elements

In the following sections, a letter is any character from the English alphabet from A to Z (both lowercase and uppercase). A digit is any character from 0 to 9. In general, spaces, tabulators, and newlines are used as delimiters between lexical units, but are otherwise ignored.

Comments

There are two type of comments: line comments and block comments. Line comments start with two slashes // and conclude at the end of the line. Block comments start with a slash and an asterisk /* and end with an asterisk and a slash */. Comments do not nest and cannot be placed inside string literals.

Identifiers

An identifier is composed of a letter and a sequence of zero or more letters, digits and the underscore character (_). Uppercase and lowercase letters are considered different. Identifiers can be of any length.

Integers

An integer literal is a sequence of one or more digits. Literals are in base ten. Their range is from 0 to 2³¹ – 1.

Strings

A string literal es a sequence of zero or more characters delimited by double quotes, for example: "this is a string". They cannot contain newline characters. A double quote character can be included in a string literal by using a pair of consecutive double quotes (""), for example: "this is another ""string""". In this example, the corresponding string is really only comprised of the following characters: this is another "string".

Booleans

Literal booleans are true and false.

Syntax

The mono-space elements represent terminal symbols (tokens).

‹program›	→	[ `const` ‹constant-declaration›+ ] [ `var` ‹variable-declaration›+ ] ‹procedure-declaration›* `program` ‹statement›* `end` `;`
‹constant-declaration›	→	‹identifier› `:=` ‹literal› `;`
‹variable-declaration›	→	‹identifier› ( `,` ‹identifier› )* `:` ‹type› `;`
‹literal›	→	‹simple-literal› \| ‹list›
‹simple-literal›	→	‹integer-literal› \| ‹string-literal› \| ‹boolean-literal›
‹type›	→	‹simple-type› \| ‹list-type›
‹simple-type›	→	`integer` \| `string` \| `boolean`
‹list-type›	→	`list` `of` ‹simple-type›
‹list›	→	`{` [ ‹simple-literal› ( `,` ‹simple-literal› )* ] `}`
‹procedure-declaration›	→	`procedure` ‹identifier› `(` ‹parameter-declaration›* `)` [ `:` ‹type› ] `;` [ `const` ‹constant-declaration›+ ] [ `var` ‹variable-declaration›+ ] `begin` ‹statement›* `end` `;`
‹parameter-declaration›	→	‹identifier› ( `,` ‹identifier› )* `:` ‹type› `;`
‹statement›	→	‹assignment-statement› \| ‹call-statement› \| ‹if-statement› \| ‹loop-statement› \| ‹for-statement› \| ‹return-statement› \| ‹exit-statement›
‹assignment-statement›	→	‹identifier› [ `[` ‹expression› `]` ] `:=` ‹expression› `;`
‹call-statement›	→	‹identifier› `(` [ ‹expression› ( `,` ‹expression› )* ] `)` `;`
‹if-statement›	→	`if` ‹expression› `then` ‹statement›* ( `elseif` ‹expression› `then` ‹statement›* )* [ `else` ‹statement›* ] `end` `;`
‹loop-statement›	→	`loop` ‹statement›* `end` `;`
‹for-statement›	→	`for` ‹identifier› `in` ‹expression› `do` ‹statement›* `end` `;`
‹return-statement›	→	`return` [ ‹expression› ] `;`
‹exit-statement›	→	`exit` `;`
‹expression›	→	‹logic-expression›
‹logic-expression›	→	‹logic-expression› ‹logic-operator› ‹relational-expression› \| ‹relational-expression›
‹logic-operator›	→	`and` \| `or` \| \| `xor`
‹relational-expression›	→	‹relational-expression› ‹relational-operator› ‹sum-expression› \| ‹sum-expression›
‹relational-operator›	→	`=` \| `<>` \| `<` \| `>` \| `<=` \| `>=`
‹sum-expression›	→	‹sum-expression› ‹sum-operator› ‹mul-expression› \| ‹mul-expression›
‹sum-operator›	→	`+` \| `-`
‹mul-expression›	→	‹mul-expression› ‹mul-operator› ‹unary-expression› \| ‹unary-expression›
‹mul-operator›	→	`*` \| `div` \| `rem`
‹unary-expression›	→	`not` ‹unary-expression› \| `-` ‹unary-expression› \| ‹simple-expression›
‹simple-expression›	→	( `(` ‹expression› `)` \| ‹call› \| ‹identifier› \| ‹literal› ) [ `[` ‹expression› `]` ]
‹call›	→	‹identifier› `(` [ ‹expression› ( `,` ‹expression› )* ] `)`

Semantics

Generalities

Every program written for the Chimera language starts its execution with the first statement after the program keyword.
An integer literal is of type integer. A string literal is of type string. A boolean literal is of type boolean. An empty list literal ({}) is compatible with any type of list.
All declared variables (local or global) take a default initial value:
- integer variables are initialized with 0.
- boolean variables are initialized with false.
- string variables are initialized with "" (empty string).
- Lists of any type are initialized with {} (empty list).
Non-empty list literals can only contain elements of the same type. Their type is list of the content type.
A list literal used in the const section must have at least one element.
Procedures that return a value do not require a return statement in order to end. If this statement is omitted, the return values should be the same as the default initial values for variables depending on the type of the procedure.
A program terminates if any runtime exception is raised.

Statements

For the following descriptions, an l-value must be an expression that refers to a variable or a list index expression (lst[index]). It cannot be a constant (an identifier declared in a const section of the program). In the case of const lists, the identifier referring to the list is what is constant, and not to the contents of the list itself.

Statement	Description
l-value `:=` exp `;`	Assign to l-value the result of evaluating exp. l-value must have been previously declared and must be the same type as exp.
proc `(` args, ...`)` `;`	Call procedure proc, evaluating (from left to right) and sending args, ... as its actual parameters. proc must have been previously declared and must not have a return type. The type and number of actual and formal parameters must match. Al parameters are passed by value.
`if` exp₁ `then` stat₁, ... ( `elseif` exp₂ `then` stat₂, ... )* [ `else` stat_n, ...] `end` `;`	Evaluate exp₁ and if it results `true`, execute all the statements stat₁, ... . Otherwise evaluate exp₂ and if it results `true`, execute statements stat₂, ... , and so on. If none of exp₁, exp₂, ... results `true`, execute the statements stat_n, ... after the `else`, in case such section is present. All expressions exp₁, exp₂, ... must be of type `boolean`.
`loop` stat, ... `end` `;`	Execute repeatedly the statements stat, ... . To end the loop an `exit` statement must be used.
`for` var `in` exp `do` stat, ... `end` `;`	Iterate over the result of evaluating exp. The element of the current iteration is assigned to var and the statements stat, ... are executed. exp must be of type list of T, and var must be a previously declared variable of type T. It is possible to terminate the loop prematurely using the `exit` statement.
`return` [ exp ] `;`	Ends a procedure returning the result of evaluating exp if provided. If exp is not provided, the procedure containing this statement must not have a declared return type, or must be a statement inside the `program` section. In case exp is provided it must be of the same type as the declared type of the procedure containing this statement.
`exit` `;`	Terminates the execution of the nearest enclosing `loop` or `for` statement in which it appears. Control passes to the statement that follows the terminated statement. It is an error to use this statement outside a looping statement.

Operators

Operator	Name	Type			Notes
Operator	Name	op1	op2	result	Notes
op₁ `and` op₂	Short Circuit Conjunction	`boolean`	`boolean`	`boolean`	Evaluates op₁. It it results `true`, evaluates and returns the result of op₂. Otherwise returns `false`.
op₁ `or` op₂	Short Circuit Disjunction	`boolean`	`boolean`	`boolean`	Evaluates op₁. If it results `false`, evaluates and returns the result of op₂. Otherwise returns `true`.
op₁ `xor` op₂	Exclusive Disjunction	`boolean`	`boolean`	`boolean`	Evaluates op₁ and op₂. If both result with the same value, returns `false`. Otherwise returns `true`.
op₁ `=` op₂	Boolean Equality	`boolean`	`boolean`	`boolean`	Returns `true` if op₁ and op₂ have the same value, otherwise returns `false`.
op₁ `=` op₂	Integer Equality	`integer`	`integer`	`boolean`	Returns `true` if op₁ and op₂ have the same value, otherwise returns `false`.
op₁ `<>` op₂	Boolean Inequality	`boolean`	`boolean`	`boolean`	Returns `true` if op₁ and op₂ have different values, otherwise returns `false`.
op₁ `<>` op₂	Integer Inequality	`integer`	`integer`	`boolean`	Returns `true` if op₁ and op₂ have different values, otherwise returns `false`.
op₁ `<` op₂	Less Than	`integer`	`integer`	`boolean`	Returns `true` if op₁ is less than op₂, otherwise returns `false`.
op₁ `>` op₂	Greater Than	`integer`	`integer`	`boolean`	Returns `true` if op₁ is greater than op₂, otherwise returns `false`.
op₁ `<=` op₂	Less Or Equal To	`integer`	`integer`	`boolean`	Returns `true` if op₁ is less or equal to op₂, otherwise returns `false`.
op₁ `>=` op₂	Greater Or Equal To	`integer`	`integer`	`boolean`	Returns `true` if op₁ is greater or equal to op₂, otherwise returns `false`.
op₁ `+` op₂	Addition	`integer`	`integer`	`integer`	Returns the addition of op₁ plus op₂. Generates an exception if the result is out of bounds.
op₁ `-` op₂	Substraction	`integer`	`integer`	`integer`	Returns the substraction of op₁ minus op₂. Generates an exception if the result is out of bounds.
op₁ `*` op₂	Multiplication	`integer`	`integer`	`integer`	Returns the multiplication of op₁ times op₂. Generates an exception if the result is out of bounds.
op₁ `div` op₂	Quotient	`integer`	`integer`	`integer`	Returns the quotient of dividing op₁ by op₂. Generates an exception if op₂ is zero.
op₁ `rem` op₂	Remainder	`integer`	`integer`	`integer`	Returns the remainder of dividing op₁ by op₂. Generates an exception if op₂ is zero.
`not` op₁	Complement	`boolean`	N/A	`boolean`	Returns `true` if op₁ is `false`, otherwise returns `false`.
`-` op₁	Negation	`integer`	N/A	`integer`	Returns the negation (reversing the sign) of op₁. Generates an exception if the result is out of bounds.
op₁`[`op₂`]`	List Index	`list` `of` T	`integer`	T	Returns the element contained in the index (the result of evaluating op₂) of the list (the result of evaluating op₁). The index of the first element is zero. Generates an exception if op₂ is out of bounds of the list.
proc`(`...`)`	Call	The number and types of the actual parameters, as well as the return type, depend on how the procedure is declared.			Returns the result of calling proc, which must of been previously declared. The type and number of actual and formal parameters must match. Parameters are passed by value. Parameters and local variables exist in a different namespace from global names. A call may be recursive.

API Specification

This section documents all the procedures from the Chimera language standard library.

Category	Procedure Signature	Description
Input/Output Operations	`WrInt( i: integer; );`	Writes to the standard output the value of `i`. Does not print a new line.
	`WrStr( s: string; );`	Writes to the standard output the value of `s`. Does not print a new line.
	`WrBool( b: boolean; );`	Writes to the standard output the value of `b`. Does not print a new line.
	`WrLn();`	Prints a new line to the standard output.
	`RdInt(): integer;`	Reads from the standard input an `integer` and returns its value. Does not return until a valid integer has been read.
	`RdStr(): string;`	Reads from the standard input a `string` (until the end of line) and returns its value.
String Operations	`AtStr( s: string; i: integer; ): string;`	Returns as a new `string` the character contained at index `i` of string `s`. First character is at index 0. Throws an exception if index `i` is out of bounds.
	`LenStr( s: string; ): integer;`	Returns the number of characters contained in string `s`.
	`CmpStr( s1, s2: string; ): integer;`	Compares lexicographically the contents of two `string`s. Returns zero if `s1` is equal to `s2`, a negative number if `s1` is less than `s2`, or a positive number if `s1` is greater than `s2`.
	`CatStr( s1, s2: string; ): string;`	Returns a new `string` resulting from the concatenation of `s1` and `s2`.
List Operations	`LenLstInt( loi: list of integer; ): integer;`	Returns the number of elements contained in `loi`.
	`LenLstStr( los: list of string; ): integer;`	Returns the number of elements contained in `los`.
	`LenLstBool( lob: list of boolean; ): integer;`	Returns the number of elements contained in `lob`.
	`NewLstInt( size: integer; ): list of integer;`	Creates and returns a new list of `integer`s of the given `size`. All list elements are initialized with zero.
	`NewLstStr( size: integer; ): list of string;`	Creates and returns a new list of `string`s of the given `size`. All list elements are initialized with `""` (empty string).
	`NewLstBool( size: integer; ): list of boolean;`	Creates and returns a new list of `boolean`s of the given `size`. All list elements are initialized with `false`.
Conversion Operations	`IntToStr( i: integer; ): string;`	Returns the result of converting `i` into a `string`.
Conversion Operations	`StrToInt( s: string; ): integer;`	Returns the result of converting `s` into an `integer`. Throws an exception if the conversion cannot be carried out.

Source Code Examples

Source file	Description	Date added
hello.chimera	Prints "Hello World!" in the screen.	26-Aug-2019
palindrome.chimera	Determines if a string is a palindrome.	26-Aug-2019
variables.chimera	Using variables and constants with different scopes.	26-Aug-2019
binary.chimera	Converts numbers into binary.	26-Aug-2019
factorial.chimera	Computes factorials using iteration and recursion.	26-Aug-2019
lists.chimera	Implementation of typical list operations.	26-Aug-2019