A small embeddable expression and function language for Go, readable by analysts and safe to evaluate on untrusted input. Immutable bindings, pattern matching and a pipe operator, with the host supplying the vocabulary of whatever domain it is embedded in.
A let cannot be reassigned, which is what makes a function free of side effects and safe to evaluate in parallel.
string, int, float, bool, datetime, duration, object, any and void, annotated at the declaration and checked there.
No side effects by default, with depth and timeout limits, so evaluating a function somebody else wrote is a bounded operation.
What the specification defines, and where it deliberately stops. Datastores, HTTP and message buses are the embedding host’s to register.
A function takes typed parameters with optional defaults and a trailing variadic, and returns a declared type. The arrow form carries a single expression and the colon form carries a body, so a one-liner never has to grow braces to become readable.
A let binds once. There is no assignment operator to reach for, so a function has no side effects to reason about and the evaluator is free to run calls in parallel.
An inline if is an expression and chains into an else-if ladder. A match arm tests a comparison, a literal, a range or a wildcard, which covers the classification shape these functions are mostly written for.
The pipe operator chains transformations in reading order, so a filter, an average and a rounding compose as three steps instead of three nested calls. It is the piece of syntax that makes the rest readable to somebody who does not write code for a living.
map, filter, reduce, sort, head, tail, unique, flatten, zip, group_by and chunk, all shaped to pipe. A filter accepts an implicit argument, so a comparison alone is a valid predicate.
sum, avg, min, max, count, stdev, variance, median and percentile, plus count_where and sum_where for the conditional cases that otherwise need a filter first.
try and catch fall back to a value. Null coalescing and optional chaining handle the absent-field case without a nested conditional at every access.
Functions live under system, shared, team, user or app namespaces, so a name is both an access-control decision and something that stays valid when the function is shared.
system::math, system::text, system::datetime, system::stats and system::collections ship preloaded. Every one of them is written in DTL itself, which is the honest test of whether the language is expressive enough.
Source to AST, with the indentation rules that let a function body skip braces.
Nine scalar types plus array variants, checked at declaration.
Sandboxed, with depth and timeout limits on every call.
Five pure namespaces under system::, none of which reach outside the interpreter.
A small embeddable expression and function language for Go, readable by analysts and safe to evaluate on untrusted input. Immutable bindings, pattern matching and a pipe operator, with the host supplying the vocabulary of whatever domain it is embedded in.
Shipping something on DTL? Nobody is listed here yet. Tell me what you built and you will be the first.
Get listed →