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## Underneath q is k

New Contributor III

The q operators and functions are a combination of optimized c functions and wrappers on top of the k language.

k preceded q by about a decade. These days you are supposed to write q code so k is not documented anymore, unfortunately parse trees and debugging require some knowledge of k.

So how do we translate between the 2 languages?

The .q namespace contains all the bits of q which are are wrappers of k and hence gives us a good starting point.

If we type lj we can see its definition, .q.lj is the fully qualified name.

``````q)lj
k){\$[\$[99h=@y;(98h=@!y)&98h=@. y;()~y];.Q.ft[,\:[;y];x];'"type"]}``````

In order to understand this we need to know what @ and ! mean in k.

So lets take .q namespace, and filter out all the functions, this gives us a good starting point for translating q into k.(I have manually rearranged the results to group similar things together)

``````\c 2000 200
q)where[1_not type'[.q]in -10 100 106 110h]#.q
neg       | -:
not       | ~:
hdel      | ~:
null      | ^:
string    | \$:
mmu       | \$
reciprocal| %:
ltime     | %:
floor     | _:
``````

There are 5 categories. We already excluded lambdas, aliases of internals like -15!, projections like ceiling(neg floor neg@), named adverb'ed operators like sums, and the k operators.

Both get and value map to the same k operator which is why they are used interchangeably when people write code. Many of the operators are overloaded like ! which does both inv and key depending on the input.

In k we use a trailing : to indicate that the operator is being used in its monadic form. The : is only required when the statement is ambiguous, the alternative to using : is to use @ or () eg: