# Built-in Data¶

## Character¶

Characters are enclosed in single quotes.

'a'
' '
'\n'


## String¶

Strings are enclosed in double quotes.

"Hello, world"


## Boolean¶

True and False are booleans.

## Scalar Values¶

In Egison, numeric scalar values (except for floats) are treated as polynomials and represented in the mathematical canonical form.

### Integer¶

1
0
-100


### Rational number¶

1 / 3
4 / 6 ---> 2 / 3


### Symbols¶

Unbound variables are interpreted as symbols.

> x + 1
x + 1
> f 2  -- uninterpreted functions
f 2


Mathematical expressions with symbols are automatically normalized into the normal form.

> (x + 1) ^ 2
x^2 + 2 * x + 1


#### Special symbols¶

Egison implements normalization algorithm for some of the common mathematical symbols.

i (imaginary unit):

> i * i
-1
> (1 + i)^2
2 * i


sqrt and rt (sqrt n denotes $$\sqrt{n}$$ and rt m n denotes $$\sqrt[m]{n}$$):

> (sqrt 2) ^ 2
2
> (rt 3 2) ^ 3
2


sin and cos:

> (sin x)^2 + (cos x)^2
1


## Float¶

1.0
1e-1 ---> 0.1
2e3  ---> 2000.0


## Inductive data¶

A variable starting with an upper-case letter is interpreted as a constructor of inductive data. You don’t need to define the inductive data before using it.

Leaf
Node 1 Leaf (Node 2 Leaf Leaf)


## Tuple (Multiple values)¶

A tuple is denoted as a sequence of elements enclosed in parentheses and separated by ,. Tuples of single element cannot be written.

() -- zero-element tuple
(1, 2)
(2, "foo", True)


## Collection¶

A collection is a sequence of elements that are enclosed in brackets and separated by ,.

[]
[1]
[1, 2]
[1, 2, 3]


## Tensor¶

A tensor is a sequence of elements enclosed in double brackets [| |] and separated by ,. The $$i$$-th element of a tensor t can be retrieved by t_i. Note that it is 1-indexed.

def t := [| 1, 2, 3, 4, 5 |]

t_1 ---> 1

-- The index can be any expression that evaluates to an integer.
t_(2+3) ---> 5

t_6 ---> Error: Tensor index out of bounds


You can get the shape of a tensor with tensorShape.

tensorShape [| 1, 2, 3, 4, 5 |] ---> [5]


Multi-dimensional tensors can be defined by nesting tensors.

[| [| 1, 2, 3 |], [| 4, 5, 6 |], [| 7, 8, 9 |] |]_1   ---> [| 1, 2, 3 |]
[| [| 1, 2, 3 |], [| 4, 5, 6 |], [| 7, 8, 9 |] |]_2_3 ---> 6


Egison prepares special syntax for tensors. See Syntax for Tensor Computation for detail.

## Hash Maps¶

A hash map is a sequence of key-value pairs enclosed in double braces {| |}. The value of a key k in a hash map h can be retrieved by h_k. If the key is not included in the keys of the hash map, the result will be undefined.

{| (1, 11) (2, 12) (3, 13) (4, 14) (5, 15) |}_1 ---> 11
{| (1, 11) (2, 12) (3, 13) (4, 14) (5, 15) |}_4 ---> 14
{| (1, 11) (2, 12) (3, 13) (4, 14) (5, 15) |}_8 ---> undefined


## IO Function¶

IO functions are functions that will yield IO operation when executed.

Any IO functions can be executed with a primitive function io.

print "foo" ---> #<io-function>


## Port¶

A port has information of a file and its access mode (input/output). You can create a port with openInputFile or openOutputFile.

## Undefined¶

undefined is a useful built-in data you can put where you have not written yet.