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Comparisons

The comparison operators compare two values of the same type and give a BOOLEAN.

Word Symbol TRUE when Example
EQUALS = the values are equal 5 EQUALS 5
GREATER THAN, ABOVE > the first is greater 10 GREATER THAN 5
LESS THAN, BELOW < the first is smaller 3 BELOW 7
AT LEAST >= the first is greater or equal 5 AT LEAST 5
AT MOST <= the first is smaller or equal 4 AT MOST 10

There is no "not equal" operator: write NOT a EQUALS b.

Example file:

-- Comparison keyword examples

-- EQUALS

-- Numeric equality
#EVAL 5 EQUALS 5
#EVAL 5 = 5

-- String equality
#EVAL "hello" EQUALS "hello"
#EVAL "hello" = "world"

-- Boolean equality
#EVAL TRUE EQUALS TRUE
#EVAL FALSE = FALSE

-- GREATER THAN / ABOVE

-- Numeric greater than
#EVAL 10 GREATER THAN 5
#EVAL 10 > 5
#EVAL 10 ABOVE 5

-- String comparison (lexicographic)
#EVAL "b" GREATER THAN "a"
#EVAL "zebra" > "apple"

-- LESS THAN / BELOW

-- Numeric less than
#EVAL 3 LESS THAN 7
#EVAL 3 < 7
#EVAL 3 BELOW 7

-- AT LEAST (>=)

#EVAL 5 AT LEAST 5
#EVAL 6 AT LEAST 5
#EVAL 4 AT LEAST 5

#EVAL 5 >= 5
#EVAL 6 >= 5

-- AT MOST (<=)

#EVAL 4 AT MOST 10
#EVAL 10 AT MOST 10
#EVAL 11 AT MOST 10

#EVAL 4 <= 10
#EVAL 10 <= 10

-- Combined Comparisons

ASSUME age IS A NUMBER

DECIDE `is of working age` IS
      age AT LEAST 18
  AND age AT MOST 65

#CHECK `is of working age`

-- Comparison in Functions

GIVEN n IS A NUMBER
GIVETH A STRING
`classification of` n MEANS
  IF n LESS THAN 0
    THEN "negative"
    ELSE IF n EQUALS 0
           THEN "zero"
           ELSE "positive"

#EVAL `classification of` (-5)
#EVAL `classification of` 0
#EVAL `classification of` 42

-- Range Check Pattern

GIVEN val IS A NUMBER
      `minimum value` IS A NUMBER
      `maximum value` IS A NUMBER
GIVETH A BOOLEAN
`is in range` val `minimum value` `maximum value` MEANS
  val AT LEAST `minimum value` AND val AT MOST `maximum value`

#EVAL `is in range` 5 1 10
#EVAL `is in range` 15 1 10
#EVAL `is in range` 1 1 10

Types

  • EQUALS works on numbers, text, booleans, values of enumerations, records and lists.
  • The ordering operators work on NUMBER, STRING (in character-code order, so "B" < "a") and BOOLEAN (FALSE is less than TRUE).
  • Dates can be compared once the daydate library is imported.

Combining comparisons

Comparisons bind more tightly than AND and OR, so no parentheses are needed:

GIVEN age IS A NUMBER
      income IS A NUMBER
GIVETH A BOOLEAN
`is eligible` age income MEANS
      age AT LEAST 18
  AND age AT MOST 65
  AND income GREATER THAN 30000

See Operators: Precedence.