calc_rational

calc_rational consists of a binary crate calc and a library crate calc_lib. calc is a CLI calculator for basic rational number arithmetic using standard operator precedence and associativity. Internally, it is based on Ratio<T> and BigInt.

Calc in action

[zack@laptop ~]$ calc
2.71828^0^3.14159 + -1!
> 0
s
> 0
@^0
> 1
s
> 1
@/3 * 3
> 1
s
> 1
|@2 - 9|^(1 - 2*3)
> 1/32768
s
> 1/32768

> 0.000030517578125
round(@, 3)
> 0
round(@, 6)
> 31/1000000

> 0.000031
2/3
> 2/3

> 0.666666667
rand()
> 939435294927814822
rand(1+9,10!)
> 2660936
1+4 mod 2 + 1
> 2
-5 mod 2
> 1
-5 mod -2
> 1
5 mod -2
> 1
9^0.5
> 3
(4/9)^(-1/2)
> 3/2
q
[zack@laptop ~]$

Expressions

The following are the list of expressions in descending order of precedence:

1. number literals, @, (), ||, round(), rand()
2. !
3. ^
4. - (unary negation operator)
5. *, /, mod
6. +, -

All binary operators are left-associative sans ^ which is right-associative.

Any expression is allowed to be enclosed in (). Note that parentheses are purely for grouping expressions; in particular, you cannot use them to represent multiplication (e.g., 4(2) is grammatically incorrect and will result in an error message).

Any expression is allowed to be enclosed in ||. This unary operator represents absolute value.

! is the factorial operator. Due to its high precedence, something like -i!^j! for i, j ∈ ℕ is the same thing as -((i!)^(j!)). If the expression preceding it does not evaluate to a non-negative integer, then an error will be displayed. Spaces and tabs are not ignored; so 1 ! is grammatically incorrect and will result in an error message.

^ is the exponentiation operator. The expression left of the operator can evaluate to any rational number; however the expression right of the operator must evaluate to an integer or ±1/2 unless the expression on the left evaluates to 0 or 1. In the event of the former, the expression right of the operator must evaluate to a non-negative rational number. In the event of the latter, the expression right of the operator can evaluate to any rational number. Note that 0^0 is defined to be 1. When the operand right of ^ evaluates to ±1/2, then the left operand must be the square of a rational number.

The unary operator - represents negation.

The operators * and / represent multiplication and division respectively. Expressions right of / must evaluate to any non-zero rational number; otherwise an error will be displayed.

The binary operator mod represents modulo such that n mod m = r = n - m*q for n,q ∈ ℤ, m ∈ ℤ\{0}, and r ∈ ℕ where r is the minimum non-negative solution.

The binary operators + and - represent addition and subtraction respectively.

With the aforementioned exception of !, all spaces and tabs before and after operators are ignored.

Round expression

round(expression, digit) rounds expression to digit-number of fractional digits. An error will be displayed if called incorrectly.

Rand expression

rand(expression, expression) generates a random 64-bit integer inclusively between the passed expressions. An error will be displayed if called incorrectly. rand() generates a random 64-bit integer.

Numbers

A number literal is a non-empty sequence of digits or a non-empty sequence of digits immediately followed by . which is immediately followed by a non-empty sequence of digits (e.g., 134.901). This means that number literals represent precisely all rational numbers that are equivalent to a ratio of a non-negative integer to a positive integer whose sole prime factors are 2 or 5. To represent all other rational numbers, the unary operator - and binary operator / must be used.

Empty expression

The empty expression (i.e., expression that at most only consists of spaces and tabs) will return the result from the previous non-(empty/store) expression in decimal form using the minimum number of digits. In the event an infinite number of digits is required, it will be rounded to 9 fractional digits using normal rounding rules first.

Store expression

To store the result of the previous non-(empty/store) expression, one simply passes s. In addition to storing the result which will subsequently be available via @, it displays the result. At most 8 results can be stored at once; at which point, results that are stored overwrite the oldest result.

Recall expression

@ is used to recall previously stored results. It can be followed by any digit from 1 to 8. If such a digit does not immediately follow it, then it will be interpreted as if there were a 1. @i returns the i-th most-previous stored result where i ∈ {1, 2, 3, 4, 5, 6, 7, 8}. Note that spaces and tabs are not ignored so @ 2 is grammatically incorrect and will result in an error message. As emphasized, it does not work on expressions; so both @@ and @(1) are grammatically incorrect.

Character encoding

All inputs must only contain the ASCII encoding of the following Unicode scalar values: 0-9, ., +, -, *, /, ^, !, mod, |, (, ), round, rand, ,, @, s, <space>, <tab>, <line feed>, <carriage return>, and q. Any other byte sequences are grammatically incorrect and will lead to an error message.

Errors

Errors due to a language violation (e.g., dividing by 0) manifest into an error message. panic!s and io::Errors caused by writing to the global standard output stream lead to program abortion. On OpenBSD-stable when compiled with the priv_sep feature, it will error if pledge(2) errors with the promise of "stdio".

Exiting

q with any number of spaces and tabs before and after or sending EOF will cause the program to terminate.

Status

This package will be actively maintained until it is deemed “feature complete”. There are really only two properties that will always be true. First, the grammar that generates a “reasonable” superset of the language will be an unambiguous context-free grammar with expression precedence and binary operator associativity embedded within. Last, the language will only deal with the field of rational numbers.

The crates are only tested on the x86_64-unknown-linux-gnu and x86_64-unknown-openbsd targets, but they should work on any Tier 1 with Host Tools target. Note one must be aware of the ASCII encoding requirement. In particular there are platforms (e.g., Windows) where the default text encoding is not a superset of ASCII.

Formal language specification

For a more precise specification of the “calc language”, one can read the calc language specification.