# Primitive operator

A **primitive operator** is a kind of operator which is defined by the language. Like a primitive function, a primitive operator is written with a single glyph in APL but may use multiple characters in other languages. The one exception to the single-glyph rule is the Outer Product, which is written `∘.`

. While some dialects consider the outer product to be a case of the dyadic operator Inner Product with a Jot (which they interpret as `⊂⍬`

) as its left operand, others consider it to be a primitive monadic operator on its own.

Primitive operators have historically been very limited, a condition which has caused greater variety in modern operators than in functions as language designers have extended the scope of operators in different ways. Iverson notation did not have a unified concept of an operator, and considered everything which is now an APL operator to be a form of special syntax. APL\360 generalized the concept of an operator, but defined only a small number of them: reductions, scans, inner products, and outer products. These operators applied only to primitive functions.

Dialects which are notable for introducing many primitive operators include SHARP APL, J, Dyalog APL (which has adopted some operators from J), and NARS2000.

APL features [edit]
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Built-ins | Primitives (functions, operators) ∙ Quad name |

Array model | Shape ∙ Rank ∙ Depth ∙ Bound ∙ Index (Indexing) ∙ Axis ∙ Ravel ∙ Ravel order ∙ Element ∙ Scalar ∙ Vector ∙ Matrix ∙ Simple scalar ∙ Simple array ∙ Nested array ∙ Cell ∙ Major cell ∙ Subarray ∙ Empty array ∙ Prototype |

Data types | Number (Boolean, Complex number) ∙ Character (String) ∙ Box ∙ Namespace ∙ Function array |

Concepts and paradigms | Conformability (Scalar extension, Leading axis agreement) ∙ Scalar function (Pervasion) ∙ Identity element ∙ Complex floor ∙ Total array ordering ∙ Tacit programming (Function composition, Close composition) ∙ Glyph |

Errors | LIMIT ERROR ∙ RANK ERROR ∙ SYNTAX ERROR ∙ DOMAIN ERROR ∙ LENGTH ERROR ∙ INDEX ERROR ∙ VALUE ERROR |