36 lines
855 B
Go
36 lines
855 B
Go
package lambda
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func (e Variable) Substitute(target string, replacement Expression) Expression {
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if e.Name() == target {
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return replacement
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}
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return e
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}
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func (e Abstraction) Substitute(target string, replacement Expression) Expression {
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if e.Parameter() == target {
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return e
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}
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body := e.Body()
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param := e.Parameter()
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if replacement.IsFree(param) {
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freeVars := replacement.GetFree()
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freeVars.Merge(body.GetFree())
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freshVar := GenerateFreshName(freeVars)
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body = body.Rename(param, freshVar)
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param = freshVar
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}
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newBody := body.Substitute(target, replacement)
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return NewAbstraction(param, newBody)
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}
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func (e Application) Substitute(target string, replacement Expression) Expression {
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abs := e.Abstraction().Substitute(target, replacement)
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arg := e.Argument().Substitute(target, replacement)
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return NewApplication(abs, arg)
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}
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