Agda-2.4.2.4: A dependently typed functional programming language and proof assistant

Agda.TypeChecking.Free

Description

Computing the free variables of a term.

The distinction between rigid and strongly rigid occurrences comes from: Jason C. Reed, PhD thesis, 2009, page 96 (see also his LFMTP 2009 paper)

The main idea is that x = t(x) is unsolvable if x occurs strongly rigidly in t. It might have a solution if the occurrence is not strongly rigid, e.g.

x = f -> suc (f (x ( y -> k))) has x = f -> suc (f (suc k))

Jason C. Reed, PhD thesis, page 106

Under coinductive constructors, occurrences are never strongly rigid. Also, function types and lambdas do not establish strong rigidity. Only inductive constructors do so. (See issue 1271).

Synopsis

Documentation

data FreeVars Source

Free variables of a term, (disjointly) partitioned into strongly and and weakly rigid variables, flexible variables and irrelevant variables.

Constructors

 FV FieldsstronglyRigidVars :: VarSetVariables under only and at least one inductive constructor(s).unguardedVars :: VarSetVariables at top or only under inductive record constructors λs and Πs. The purpose of recording these separately is that they can still become strongly rigid if put under a constructor whereas weakly rigid ones stay weakly rigid.weaklyRigidVars :: VarSetOrdinary rigid variables, e.g., in arguments of variables.flexibleVars :: VarSetVariables occuring in arguments of metas. These are only potentially free, depending how the meta variable is instantiated.irrelevantVars :: VarSetVariables in irrelevant arguments and under a `DontCare`, i.e., in irrelevant positions.unusedVars :: VarSetVariables in `UnusedArg`uments.

Instances

 Source Source Source Free variable sets form a monoid under `union`. Source

type Free a = Free' a Any Source

type FreeVS a = Free' a VarSet Source

Where should we skip sorts in free variable analysis?

Constructors

 IgnoreNot Do not skip. IgnoreInAnnotations Skip when annotation to a type. IgnoreAll Skip unconditionally.

Instances

 Source Source

allFreeVars :: Free' a VarSet => a -> VarSet Source

Collect all free variables.

allRelevantVars :: Free' a VarSet => a -> VarSet Source

Collect all relevant free variables.

allRelevantVarsIgnoring :: Free' a VarSet => IgnoreSorts -> a -> VarSet Source

Collect all relevant free variables, possibly ignoring sorts.

freeIn :: Free a => Nat -> a -> Bool Source

isBinderUsed :: Free a => Abs a -> Bool Source

Is the variable bound by the abstraction actually used?

relevantIn :: Free a => Nat -> a -> Bool Source

data Occurrence Source

Constructors

 NoOccurrence Irrelevantly StronglyRigid Under at least one and only inductive constructors. Unguarded In top position, or only under inductive record constructors. WeaklyRigid In arguments to variables and definitions. Flexible In arguments of metas. Unused

Instances

 Source Source

occurrence :: FreeV a => Nat -> a -> Occurrence Source

Compute an occurrence of a single variable in a piece of internal syntax.

closed :: Free' a All => a -> Bool Source

Is the term entirely closed (no free variables)?

freeVars :: (Monoid c, Singleton Variable c, Free' a c) => a -> c Source

Doesn't go inside solved metas, but collects the variables from a metavariable application `X ts` as `flexibleVars`.