test_pattern: Test if a pattern matches an expression

In mailund/pmatch: Pattern Matching

Description

Test if a value, expr, created from constructors matches a pattern of constructors. The test_pattern_ function requires that test_expr is a quoted expression while the test_pattern function expects a bare expression and will quote it itself.

Usage

test_pattern_(
  expr,
  test_expr,
  eval_env = rlang::caller_env(),
  match_parent_env = rlang::caller_env()
)

test_pattern(
  expr,
  test_expr,
  eval_env = rlang::caller_env(),
  match_parent_env = rlang::caller_env()
)

Arguments

expr	A value created using constructors.
test_expr	A constructor pattern to test expr against.
eval_env	The environment where constructors can be found.
match_parent_env	Environment to use as the parent of the match bindings we return. This parameter enables you provide additional values to the environment where match-expressions are evaluated.

Value

NULL if the pattern does not match or an environment with bound variables if it does.

Functions

• test_pattern_: Version that quotes test_expr itself.

• test_pattern: Version that quotes test_expr itself.

Examples

type := ZERO | ONE(x) | TWO(x, y)
zero <- ZERO
one <- ONE(1)
two <- TWO(1, 2)

as.list(test_pattern(zero, ZERO)) # returns an empty binding
test_pattern_(one, quote(ZERO)) # returns NULL
as.list(test_pattern_(one, quote(ONE(v)))) # returns a binding for v
as.list(test_pattern(two, TWO(v, w))) # returns a binding for v and w

mailund/pmatch documentation built on Feb. 4, 2020, 4:55 a.m.