Reader Operators

Reader operators allow the reader to re-arrange expressions before passing them onto the evaluator.

The obvious use of operators is for infix expressions like regular arithmetic, 1 + 2. Idio expects the function to be the first element of any form so without any re-arrangement it would try to invoke the function 1.

You can define postfix operators as well although there are very few defined by default.

Arithmetic is usually a binary operation in that it expects a number either side of the operator. Other infix operators like job-control’s | operator can expect any number of arguments either side of the operator and potentially more than one instance of itself in the same expression.

Like C arithmetic precedence, operators are given a precedence which allows them to gather elements of expressions into groups before recursing the operator expansion code on those groups.

Consider:

find . -name foo 2> "/dev/null" | xargs wc -l

Here we would expect | to have a high precedence to construct two sub-expressions:

• find . -name foo 2> "/dev/null"

• xargs wc -l

Recursing the operator expansion into the first sub-expression we would find the I/O redirection operator, 2>, also from job-control, which would distinguish find . -name foo from the I/O redirection target "/dev/null"

Operators are another spin on templates and like them are regular functions which return an expression to be evaluated.

The actual expansion of the | operator is pages of code, see lib/job-control.idio for more details.

• Operator Predicates
• Operator Constructors
• Operator Functions

Last built at 2024-12-21T07:10:42Z+0000 from 62cca4c (dev) for Idio 0.3.b.6