Language

Basic Types

Phel's primitive values: nil, booleans, numbers, strings, keywords, plus truthiness, equality, and reader literals

Data structures

Phel's persistent collections: lists, vectors, maps, sets, structs, plus core functions like conj, assoc, get-in, and into

Global and local bindings

Bind values to names with def and let, rebind dynamic vars with binding, and manage mutable state with atoms

Control flow

Branch, loop, and build collections with if, cond, case, loop/recur, for, and thread macros like cond->

Functions and Recursion

Define functions with fn and defn, use multi-arity and variadics, recurse safely with recur, and dispatch with multimethods

Destructuring

Bind names to values inside vectors, lists, and maps by shape in let, function params, and loop

Error handling

Throw and catch exceptions, handle PHP exceptions, attach data with ex-info, and decide when to throw vs return nil

Namespaces

Declare namespaces with ns, require Phel modules and PHP classes, and use aliases, :refer, and namespaced keywords

Interfaces

Define contracts with definterface, implement them in structs, extend types with protocols, and dispatch via hierarchies

Macros

Write compile-time code that rewrites code: defmacro, quasiquote, macroexpand, gensym hygiene, and when a macro is worth it

Lazy Sequences

Defer computation with lazy-seq and lazy-cat, build infinite sequences, and avoid the common laziness pitfalls.

Transducers

Build composable, allocation-free transformation pipelines that decouple the transformation from the consumer, and write your own custom transducers

Reader Shortcuts

Compact catalog of the reader macros and special syntax the Phel reader expands at read time: literals, quote/quasiquote, tagged literals, anonymous functions, reader conditionals, and metadata.

Reader Conditionals

Write platform-specific code in shared .cljc source files with #?() and #?@(), resolved at parse time using :phel and :default keys

Numeric Tower

Phel's five numeric shapes (int, BigInt, Ratio, BigDecimal, float), when each appears, and how arithmetic dispatches across them

Async & Concurrency

Run work concurrently with Phel's two fiber-based layers: top-level promises and futures, plus an AMPHP event loop for timers, IO, and fan-out