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# Comparison RPN Operators
gt provides six comparison operators, each with both a named and a symbolic alias. All operators are metric-aware — they convert values to base units before comparing. Results are boolean (`true` / `false`) and coerce into arithmetic (true → 1, false → 0).
## Operators
| Operator | Alias | RPN | Infix | Description |
|----------|-------|-------------|---------|-----------------|
| `gt` | `>` | `a b gt` | `a > b` | Greater than |
| `lt` | `<` | `a b lt` | `a < b` | Less than |
| `gte` | `>=` | `a b gte` | `a >= b`| Greater/equal |
| `lte` | `<=` | `a b lte` | `a <= b`| Less/equal |
| `eq` | `==` | `a b eq` | `a == b`| Equal |
| `neq` | `!=` | `a b neq` | `a != b`| Not equal |
All operators pop two values (`a` first, then `b`) from the stack, compare them, and push the boolean result.
## Truth Table
### `gt` / `>`
| a | b | Result |
|-----|-----|--------|
| 5 | 3 | true |
| 3 | 5 | false |
| 5 | 5 | false |
```
$ gt '5 3 gt'
true
$ gt '5 3 >'
true
```
### `lt` / `<`
| a | b | Result |
|-----|-----|--------|
| 3 | 5 | true |
| 5 | 3 | false |
| 5 | 5 | false |
### `gte` / `>=`
| a | b | Result |
|-----|-----|--------|
| 5 | 3 | true |
| 5 | 5 | true |
| 3 | 5 | false |
### `lte` / `<=`
| a | b | Result |
|-----|-----|--------|
| 3 | 5 | true |
| 5 | 5 | true |
| 5 | 3 | false |
### `eq` / `==`
| a | b | Result |
|-----|-----|--------|
| 5 | 5 | true |
| 5 | 3 | false |
### `neq` / `!=`
| a | b | Result |
|-----|-----|--------|
| 5 | 3 | true |
| 5 | 5 | false |
## Metric-Aware Comparison
Comparison operators convert operands to base units before comparing, so different units within the same category can be compared directly.
### Same category, different units
```
$ gt '1km 1000m eq'
true
$ gt '1km 500m gt'
true
$ gt '500m 1km lt'
true
```
### Data storage (decimal SI prefixes)
```
$ gt '1GB 1000MB gte'
true
$ gt '1GB 1000MB gt'
false
$ gt '1GB 1024MB eq'
false
```
`1GB` equals exactly `1000MB` (decimal SI), so `gt` is false and `gte` is true. `1024MB` is not equal to `1GB`.
### Network throughput
```
$ gt '100Mbps 50Mbps gt'
true
$ gt '1Gbps 1000Mbps eq'
true
```
### Incompatible categories
Comparing values from different metric categories produces an error:
```
$ gt '5m 3kg gt'
Error: incompatible metric categories
```
Unitless numbers are always compatible with any metric value.
## Boolean Coercion in Arithmetic
Boolean results coerce to numbers: `true` → 1, `false` → 0. This lets comparison results flow directly into arithmetic.
### Conditional addition
```
$ gt '5 3 gt 1 +'
2
```
`5 > 3` is true (1), so `1 + 1 = 2`.
```
$ gt '3 5 gt 1 +'
1
```
`3 > 5` is false (0), so `0 + 1 = 1`.
### Conditional multiplication
```
$ gt '5 3 gt 10 *'
10
$ gt '3 5 gt 10 *'
0
```
### Chained comparisons
```
$ gt '9 3 gt 4 5 lt +'
2
```
`9 > 3` (true/1) + `4 < 5` (true/1) = `1 + 1 = 2`.
### Boolean arithmetic with subtraction
```
$ gt '5 3 gt 0 -'
1
$ gt '5 5 eq 1 -'
0
```
## Examples
### Threshold checks
```
$ gt '85 80 gt'
true
```
CPU at 85%, threshold at 80% — alert.
### Range validation
Check that a value falls within acceptable bounds:
```
$ gt '72 68 gte 100 lte +'
2
```
Temperature 72°F: `72 >= 68` (true/1) + `72 <= 100` (true/1) = 2 (both checks pass).
```
$ gt '105 68 gte 100 lte +'
1
```
Temperature 105°F: `105 >= 68` (true/1) + `105 <= 100` (false/0) = 1 (outside range).
When the sum is 2, the value is within range. Any other result means at least one check failed.
### Metric validation
```
$ gt '100Mbps 50Mbps gt'
true
```
Download speed 100Mbps exceeds minimum 50Mbps — pass.
### Counting conditions
Sum boolean results to count how many conditions are met:
```
$ gt '10 5 gt 20 15 gt 30 25 gt +'
3
```
All three conditions are true: `1 + 1 + 1 = 3`.
### Guard expressions
Multiply a value by a condition to guard it:
```
$ gt '99 80 gt *'
99
```
Value 99 is used because `99 > 80` is true (1): `99 * 1 = 99`.
```
$ gt '50 80 gt *'
0
```
Value 50 is discarded because `50 > 80` is false (0): `50 * 0 = 0`.
## Edge Cases
### Zero comparisons
```
$ gt '0 0 eq'
true
$ gt '0 0 neq'
false
$ gt '0 1 lt'
true
```
### Negative numbers
```
$ gt '-1 0 lt'
true
$ gt '-5 -3 lt'
true
```
### Insufficient operands
Any comparison on an empty or single-element stack returns an error:
```
$ gt 'gt'
Error: stack is empty
$ gt '5 gt'
Error: stack has insufficient operands
```
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