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58 lines
1.2 KiB
58 lines
1.2 KiB
package vm
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import (
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"errors"
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)
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// ErrNameNotDefined is returned from Scope.Resolve when a name could not be
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// resolved within a Scope.
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var ErrNameNotDefined = errors.New("not defined")
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// Scope encapsulates a set of name->Value mappings.
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type Scope interface {
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// Resolve accepts a name and returns an Value, or returns
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// ErrNameNotDefined.
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Resolve(string) (Value, error)
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}
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// ScopeMap implements the Scope interface.
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type ScopeMap map[string]Value
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var _ Scope = ScopeMap{}
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// Resolve uses the given name as a key into the ScopeMap map, and
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// returns the Operation held there for the key, if any.
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func (m ScopeMap) Resolve(name string) (Value, error) {
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v, ok := m[name]
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if !ok {
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return Value{}, ErrNameNotDefined
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}
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return v, nil
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}
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type scopeWith struct {
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Scope // parent
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name string
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val Value
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}
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// ScopeWith returns a copy of the given Scope, except that evaluating the given
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// name will always return the given Value.
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func ScopeWith(scope Scope, name string, val Value) Scope {
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return &scopeWith{
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Scope: scope,
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name: name,
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val: val,
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}
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}
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func (s *scopeWith) Resolve(name string) (Value, error) {
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if name == s.name {
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return s.val, nil
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}
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return s.Scope.Resolve(name)
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}
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