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Pragma syntax

Pragmas can be associated with identifiers by placing a pragma comment just before identifier declaration. For example

{-# inline: true #-}
f : Nat -> Nat;

associates the inline pragma with value true to the identifier f.

Multiple pragmas associated with one identifier are separated by commas:

{-# inline: true, unroll: 100 #-}
f : Nat -> Nat;

Pragmas associated with a module are inherited by all definitions in the module, unless overridden. For example,

{-# inline: true #-}
module M;
  f : Nat -> Nat := ..;

  g : Nat -> Nat := ..;

  {-# inline: false #-}
  h : Nat -> Nat := ..;

enables inlining for f, g and disables it for h.

The pragmas are just mappings in YAML syntax, except that the outermost braces are not required for the top-level mapping if it is on one line. Since pragmas are supposed to be backwards-compatible, the compiler will ignore any pragmas it doesn't recognize. Pragmas control how code is compiled by providing annotations to the compiler, but they have no semantic significance - removing all pragmas should not change the meaning of the program.

Available pragmas

We list all currently recognized pragmas. Below b denotes a boolean (true or false), and n denotes a non-negative number.

  • inline: b

Indicates whether a function should be inlined:

  • true: always inline when fully applied,
  • false: never inline (also disables automatic inlining).

When the inline pragma is not present and the optimization level is at least 1, a non-recursive fully applied function is automatically inlined if the height of the body term does not exceed the inlining depth limit, which can be specified with the --inline option to the compile command.

  • inline: n

Indicates that a partial application of the function with at least n explicit arguments should always be inlined. For example, with the definition

{-# inline: 2 #-}
compose {A B C} (f : B -> C) (g : A -> B) (x : A) : C := f (g x);

in the expression compose f g the function compose will be inlined, but in compose f it won't be.

  • unroll: n

Set the maximum recursion unrolling depth to n. This affects only the vampir and geb backends.

  • argnames: [arg1, .., argn]

Set the names of function arguments in the generated output to arg1,..,argn. This is useful primarily with the vampir backend to name VampIR input variables.

  • format: b

Enable or disable formatting for the specified module. Adding the format: false pragma before a module makes the formatter ignore the module and output it verbatim.