# Property and Invariant Functions¶

These are functions available in properties and invariants – not necessarily in executable Pact code. All of these functions are available in properties, but only a subset are available in invariants. As a general rule, invariants have vocabulary for talking about the shape of data, whereas properties also add vocabulary for talking about function inputs and outputs, and database interactions. Each function also explicitly says whether it’s available in just properties, or invariants as well.

## Numerical operators¶

### +¶

```(+ x y)
```
• takes `x`: a
• takes `y`: a
• produces a
• where a is of type `integer` or `decimal`

Supported in either invariants or properties.

### -¶

```(- x y)
```
• takes `x`: a
• takes `y`: a
• produces a
• where a is of type `integer` or `decimal`

Subtraction of integers and decimals.

Supported in either invariants or properties.

### *¶

```(* x y)
```
• takes `x`: a
• takes `y`: a
• produces a
• where a is of type `integer` or `decimal`

Multiplication of integers and decimals.

Supported in either invariants or properties.

### /¶

```(/ x y)
```
• takes `x`: a
• takes `y`: a
• produces a
• where a is of type `integer` or `decimal`

Division of integers and decimals.

Supported in either invariants or properties.

### ^¶

```(^ x y)
```
• takes `x`: a
• takes `y`: a
• produces a
• where a is of type `integer` or `decimal`

Exponentiation of integers and decimals.

Supported in either invariants or properties.

### log¶

```(log b x)
```
• takes `b`: a
• takes `x`: a
• produces a
• where a is of type `integer` or `decimal`

Logarithm of `x` base `b`.

Supported in either invariants or properties.

### -¶

```(- x)
```
• takes `x`: a
• produces a
• where a is of type `integer` or `decimal`

Negation of integers and decimals.

Supported in either invariants or properties.

### sqrt¶

```(sqrt x)
```
• takes `x`: a
• produces a
• where a is of type `integer` or `decimal`

Square root of integers and decimals.

Supported in either invariants or properties.

### ln¶

```(ln x)
```
• takes `x`: a
• produces a
• where a is of type `integer` or `decimal`

Logarithm of integers and decimals base e.

Supported in either invariants or properties.

### exp¶

```(exp x)
```
• takes `x`: a
• produces a
• where a is of type `integer` or `decimal`

Exponential of integers and decimals. e raised to the integer or decimal `x`.

Supported in either invariants or properties.

### abs¶

```(abs x)
```
• takes `x`: a
• produces a
• where a is of type `integer` or `decimal`

Absolute value of integers and decimals.

Supported in either invariants or properties.

### round¶

```(round x)
```
• takes `x`: `decimal`
• produces `integer`
```(round x prec)
```
• takes `x`: `decimal`
• takes `prec`: `integer`
• produces `integer`

Banker’s rounding value of decimal `x` as integer, or to `prec` precision as decimal.

Supported in either invariants or properties.

### ceiling¶

```(ceiling x)
```
• takes `x`: `decimal`
• produces `integer`
```(ceiling x prec)
```
• takes `x`: `decimal`
• takes `prec`: `integer`
• produces `integer`

Rounds the decimal `x` up to the next integer, or to `prec` precision as decimal.

Supported in either invariants or properties.

### floor¶

```(floor x)
```
• takes `x`: `decimal`
• produces `integer`
```(floor x prec)
```
• takes `x`: `decimal`
• takes `prec`: `integer`
• produces `integer`

Rounds the decimal `x` down to the previous integer, or to `prec` precision as decimal.

Supported in either invariants or properties.

### mod¶

```(mod x y)
```
• takes `x`: `integer`
• takes `y`: `integer`
• produces `integer`

Integer modulus

Supported in either invariants or properties.

## Bitwise operators¶

### &¶

```(& x y)
```
• takes `x`: `integer`
• takes `y`: `integer`
• produces `integer`

Bitwise and

Supported in either invariants or properties.

### |¶

```(| x y)
```
• takes `x`: `integer`
• takes `y`: `integer`
• produces `integer`

Bitwise or

Supported in either invariants or properties.

### xor¶

```(xor x y)
```
• takes `x`: `integer`
• takes `y`: `integer`
• produces `integer`

Bitwise exclusive-or

Supported in either invariants or properties.

### shift¶

```(shift x y)
```
• takes `x`: `integer`
• takes `y`: `integer`
• produces `integer`

Shift `x` `y` bits left if `y` is positive, or right by `-y` bits otherwise.

Supported in either invariants or properties.

### ~¶

```(~ x)
```
• takes `x`: `integer`
• produces `integer`

Reverse all bits in `x`

Supported in either invariants or properties.

## Logical operators¶

### >¶

```(> x y)
```
• takes `x`: a
• takes `y`: a
• produces `bool`
• where a is of type `integer` or `decimal`

True if `x` > `y`

Supported in either invariants or properties.

### <¶

```(< x y)
```
• takes `x`: a
• takes `y`: a
• produces `bool`
• where a is of type `integer` or `decimal`

True if `x` < `y`

Supported in either invariants or properties.

### >=¶

```(>= x y)
```
• takes `x`: a
• takes `y`: a
• produces `bool`
• where a is of type `integer` or `decimal`

True if `x` >= `y`

Supported in either invariants or properties.

### <=¶

```(<= x y)
```
• takes `x`: a
• takes `y`: a
• produces `bool`
• where a is of type `integer` or `decimal`

True if `x` <= `y`

Supported in either invariants or properties.

### =¶

```(= x y)
```
• takes `x`: a
• takes `y`: a
• produces `bool`
• where a is of type `integer`, `decimal`, `string`, `time`, `bool`, `object`, or `keyset`

True if `x` = `y`

Supported in either invariants or properties.

### !=¶

```(!= x y)
```
• takes `x`: a
• takes `y`: a
• produces `bool`
• where a is of type `integer`, `decimal`, `string`, `time`, `bool`, `object`, or `keyset`

True if `x` != `y`

Supported in either invariants or properties.

### and¶

```(and x y)
```
• takes `x`: `bool`
• takes `y`: `bool`
• produces `bool`

Short-circuiting logical conjunction

Supported in either invariants or properties.

### or¶

```(or x y)
```
• takes `x`: `bool`
• takes `y`: `bool`
• produces `bool`

Short-circuiting logical disjunction

Supported in either invariants or properties.

### not¶

```(not x)
```
• takes `x`: `bool`
• produces `bool`

Logical negation

Supported in either invariants or properties.

### when¶

```(when x y)
```
• takes `x`: `bool`
• takes `y`: `bool`
• produces `bool`

Logical implication. Equivalent to `(or (not x) y)`.

Supported in either invariants or properties.

### and?¶

```(and? f g a)
```
• takes `f`: a -> `bool`
• takes `g`: a -> `bool`
• takes `a`: a
• produces `bool`

`and` the results of applying both `f` and `g` to `a`

Supported in either invariants or properties.

### or?¶

```(or? f g a)
```
• takes `f`: a -> `bool`
• takes `g`: a -> `bool`
• takes `a`: a
• produces `bool`

`or` the results of applying both `f` and `g` to `a`

Supported in either invariants or properties.

## Object operators¶

### at¶

```(at k o)
```
• takes `k`: `string`
• takes `o`: `object`
• produces a
```(at i l)
```
• takes `i`: `integer`
• takes `o`: `list`
• produces `bool`

projection

Supported in either invariants or properties.

### +¶

```(+ x y)
```
• takes `x`: `object`
• takes `y`: `object`
• produces `object`

Object merge

Supported in either invariants or properties.

### drop¶

```(drop keys o)
```
• takes `keys`: [`string`]
• takes `o`: `object`
• produces `object`

drop entries having the specified keys from an object

Supported in either invariants or properties.

### take¶

```(take keys o)
```
• takes `keys`: [`string`]
• takes `o`: `object`
• produces `object`

take entries having the specified keys from an object

Supported in either invariants or properties.

### length¶

```(length o)
```
• takes `o`: `object`
• produces `integer`

the number of key-value pairs in the object

Supported in either invariants or properties.

## List operators¶

### at¶

```(at k l)
```
• takes `k`: `string`
• takes `l`: [a]
• produces a
```(at i l)
```
• takes `i`: `integer`
• takes `o`: `list`
• produces `bool`

projection

Supported in either invariants or properties.

### length¶

```(length s)
```
• takes `s`: [a]
• produces `integer`

List length

Supported in either invariants or properties.

### contains¶

```(contains x xs)
```
• takes `x`: a
• takes `xs`: [a]
• produces `bool`
```(contains k o)
```
• takes `k`: `string`
• takes `o`: `object`
• produces `bool`
```(contains value string)
```
• takes `value`: `string`
• takes `string`: `string`
• produces `bool`

List / string / object contains

Supported in either invariants or properties.

### reverse¶

```(reverse xs)
```
• takes `xs`: [a]
• produces [a]

reverse a list of values

Supported in either invariants or properties.

### sort¶

```(sort xs)
```
• takes `xs`: [a]
• produces [a]

sort a list of values

Supported in either invariants or properties.

### drop¶

```(drop n xs)
```
• takes `n`: `integer`
• takes `xs`: [a]
• produces [a]

drop the first `n` values from the beginning of a list (or the end if `n` is negative)

Supported in either invariants or properties.

### take¶

```(take n xs)
```
• takes `n`: `integer`
• takes `xs`: [a]
• produces [a]

take the first `n` values from `xs` (taken from the end if `n` is negative)

Supported in either invariants or properties.

### make-list¶

```(make-list n a)
```
• takes `n`: `integer`
• takes `a`: a
• produces [a]

create a new list with `n` copies of `a`

Supported in either invariants or properties.

### map¶

```(map f as)
```
• takes `f`: a -> b
• takes `as`: [a]
• produces [b]

apply `f` to each element in a list

Supported in either invariants or properties.

### filter¶

```(filter f as)
```
• takes `f`: a -> `bool`
• takes `as`: [a]
• produces [a]

filter a list by keeping the values for which `f` returns `true`

Supported in either invariants or properties.

### fold¶

```(fold f a bs)
```
• takes `f`: a -> b -> a
• takes `a`: a
• takes `bs`: [b]
• produces [a]

reduce a list by applying `f` to each element and the previous result

Supported in either invariants or properties.

## String operators¶

### length¶

```(length s)
```
• takes `s`: `string`
• produces `integer`

String length

Supported in either invariants or properties.

### +¶

```(+ s t)
```
• takes `s`: `string`
• takes `t`: `string`
• produces `string`
```(+ s t)
```
• takes `s`: [a]
• takes `t`: [a]
• produces [a]

String / list concatenation

Supported in either invariants or properties.

### str-to-int¶

```(str-to-int s)
```
• takes `s`: `string`
• produces `integer`
```(str-to-int b s)
```
• takes `b`: `integer`
• takes `s`: `string`
• produces `integer`

String to integer conversion

Supported in either invariants or properties.

## Temporal operators¶

```(add-time t s)
```
• takes `t`: `time`
• takes `s`: a
• produces `time`
• where a is of type `integer` or `decimal`

Supported in either invariants or properties.

## Quantification operators¶

### forall¶

```(forall (x:string) y)
```
• binds `x`: a
• takes `y`: r
• produces r
• where a is any type
• where r is any type

Bind a universally-quantified variable

Supported in properties only.

### exists¶

```(exists (x:string) y)
```
• binds `x`: a
• takes `y`: r
• produces r
• where a is any type
• where r is any type

Bind an existentially-quantified variable

Supported in properties only.

### column-of¶

```(column-of t)
```
• takes `t`: `table`
• produces `type`

The type of `column`s for a given `table`. Commonly used in conjunction with quantification; e.g.: `(exists (col:(column-of accounts)) (column-written accounts col))`.

Supported in properties only.

## Transactional operators¶

### abort¶

```abort
```
• of type `bool`

Whether the transaction aborts. This function is only useful when expressing propositions that do not assume transaction success. Propositions defined via `property` implicitly assume transaction success. We will be adding a new mode in which to use this feature in the future – please let us know if you need this functionality.

Supported in properties only.

### success¶

```success
```
• of type `bool`

Whether the transaction succeeds. This function is only useful when expressing propositions that do not assume transaction success. Propositions defined via `property` implicitly assume transaction success. We will be adding a new mode in which to use this feature in the future – please let us know if you need this functionality.

Supported in properties only.

### governance-passes¶

```governance-passes
```
• of type `bool`

Whether the governance predicate passes. For keyset-based governance, this is the same as something like `(authorized-by 'governance-ks-name)`. Pact’s property checking system currently does not analyze the body of a capability when it is used for governance due to challenges around capabilities making DB modifications – the system currently assumes that a capability-based governance predicate is equally capable of succeeding or failing. This feature allows describing the scenarios where the predicate passes or fails.

Supported in properties only.

### result¶

```result
```
• of type r
• where r is any type

The return value of the function under test

Supported in properties only.

## Database operators¶

### table-written¶

```(table-written t)
```
• takes `t`: a
• produces `bool`
• where a is of type `table` or `string`

Whether a table is written in the function under analysis

Supported in properties only.

```(table-read t)
```
• takes `t`: a
• produces `bool`
• where a is of type `table` or `string`

Whether a table is read in the function under analysis

Supported in properties only.

### cell-delta¶

```(cell-delta t c r)
```
• takes `t`: a
• takes `c`: b
• takes `r`: `string`
• produces c
• where a is of type `table` or `string`
• where b is of type `column` or `string`
• where c is of type `integer` or `decimal`

The difference in a cell’s value before and after the transaction

Supported in properties only.

### column-delta¶

```(column-delta t c)
```
• takes `t`: a
• takes `c`: b
• produces c
• where a is of type `table` or `string`
• where b is of type `column` or `string`
• where c is of type `integer` or `decimal`

The difference in a column’s total summed value before and after the transaction

Supported in properties only.

### column-written¶

```(column-written t c)
```
• takes `t`: a
• takes `c`: b
• produces `bool`
• where a is of type `table` or `string`
• where b is of type `column` or `string`

Whether a column is written to in a transaction

Supported in properties only.

```(column-read t c)
```
• takes `t`: a
• takes `c`: b
• produces `bool`
• where a is of type `table` or `string`
• where b is of type `column` or `string`

Whether a column is read from in a transaction

Supported in properties only.

```(row-read t r)
```
• takes `t`: a
• takes `r`: `string`
• produces `bool`
• where a is of type `table` or `string`

Whether a row is read in the function under analysis

Supported in properties only.

### row-written¶

```(row-written t r)
```
• takes `t`: a
• takes `r`: `string`
• produces `bool`
• where a is of type `table` or `string`

Whether a row is written in the function under analysis

Supported in properties only.

```(row-read-count t r)
```
• takes `t`: a
• takes `r`: `string`
• produces `integer`
• where a is of type `table` or `string`

The number of times a row is read during a transaction

Supported in properties only.

### row-write-count¶

```(row-write-count t r)
```
• takes `t`: a
• takes `r`: `string`
• produces `integer`
• where a is of type `table` or `string`

The number of times a row is written during a transaction

Supported in properties only.

### row-exists¶

```(row-exists t r time)
```
• takes `t`: a
• takes `r`: `string`
• takes `time`: one of {“before”,“after”}
• produces `bool`
• where a is of type `table` or `string`

Whether a row exists before or after a transaction

Supported in properties only.

```(read t r)
```
• takes `t`: a
• takes `r`: `string`
• takes `time`: one of {“before”,“after”}
• produces `object`
• where a is of type `table` or `string`

The value of a read before or after a transaction

Supported in properties only.

## Authorization operators¶

### authorized-by¶

```(authorized-by k)
```
• takes `k`: `string`
• produces `bool`

Whether the named keyset/guard is satisfied by the executing transaction

Supported in properties only.

### row-enforced¶

```(row-enforced t c r)
```
• takes `t`: a
• takes `c`: b
• takes `r`: `string`
• produces `bool`
• where a is of type `table` or `string`
• where b is of type `column` or `string`

Whether the keyset in the row is enforced by the function under analysis

Supported in properties only.

## Function operators¶

### identity¶

```(identity a)
```
• takes `a`: a
• produces a
• where a is of type `table` or `string`

identity returns its argument unchanged

Supported in either invariants or properties.

### constantly¶

```(constantly a)
```
• takes `a`: a
• takes `b`: b
• produces a

constantly returns its first argument, ignoring the second

Supported in either invariants or properties.

### compose¶

```(compose f g)
```
• takes `f`: a -> b
• takes `g`: b -> c
• produces c

compose two functions

Supported in either invariants or properties.

## Other operators¶

### where¶

```(where field f obj)
```
• takes `field`: `string`
• takes `f`: a -> `bool`
• takes `obj`: `object`
• produces `bool`

utility for use in `filter` and `select` applying `f` to `field` in `obj`

Supported in either invariants or properties.

### typeof¶

```(typeof a)
```
• takes `a`: a
• produces `string`

return the type of `a` as a string

Supported in either invariants or properties.