Standard library: Association lists #231
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| Original file line number | Diff line number | Diff line change |
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| /* | ||
| * Association Lists, a la functional programming, in ActorScript. | ||
| */ | ||
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| // polymorphic association linked lists between keys and values | ||
| type AssocList<K,V> = List<(K,V)>; | ||
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| let AssocList = new { | ||
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Contributor
There was a problem hiding this comment. I'd be tempted to abstract
Contributor
Author
There was a problem hiding this comment. I agree that generative functors (or existentials) would be really nice here. It's not too painful to pass around these equality functions, but if there were a bunch more operations in the mix, it might get unwieldy after a while, or require some explicit structures, or both. |
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| // find the value associated with a given key, or null if absent. | ||
| func find<K,V>(al : AssocList<K,V>, | ||
| k:K, | ||
| k_eq:(K,K)->Bool) | ||
| : ?V | ||
| { | ||
| func rec(al:AssocList<K,V>) : ?V { | ||
| switch (al) { | ||
| case (null) null; | ||
| case (?((hd_k, hd_v), tl)) { | ||
| if (k_eq(k, hd_k)) { | ||
| ?hd_v | ||
| } else { | ||
| rec(tl) | ||
| } | ||
| }; | ||
| }}; | ||
| rec(al) | ||
| }; | ||
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| // replace the value associated with a given key, or add it, if missing. | ||
| // returns old value, or null, if no prior value existed. | ||
| func replace<K,V>(al : AssocList<K,V>, | ||
| k:K, | ||
| k_eq:(K,K)->Bool, | ||
| ov: ?V) | ||
| : (AssocList<K,V>, ?V) | ||
| { | ||
| func rec(al:AssocList<K,V>) : (AssocList<K,V>, ?V) { | ||
| switch (al) { | ||
| case (null) { | ||
| switch ov { | ||
| case (null) (null, null); | ||
| case (?v) (?((k, v), null), null); | ||
| } | ||
| }; | ||
| case (?((hd_k, hd_v), tl)) { | ||
| if (k_eq(k, hd_k)) { | ||
| // if value is null, remove the key; otherwise, replace key's old value | ||
| // return old value | ||
| switch ov { | ||
| case (null) (tl, ?hd_v); | ||
| case (?v) (?((hd_k, v), tl), ?hd_v); | ||
| } | ||
| } else { | ||
| let (tl2, old_v) = rec(tl); | ||
| (?((hd_k, hd_v), tl2), old_v) | ||
| } | ||
| }; | ||
| }}; | ||
| rec(al) | ||
| }; | ||
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| // The key-value pairs of the final list consist of those pairs of | ||
| // the left list whose keys are not present in the right list; the | ||
| // values of the right list are irrelevant. | ||
| func diff<K,V,W>(al1: AssocList<K,V>, | ||
| al2: AssocList<K,W>, | ||
| keq: (K,K)->Bool) | ||
| : AssocList<K,V> | ||
| { | ||
| func rec(al1:AssocList<K,V>) : AssocList<K,V> = { | ||
| switch al1 { | ||
| case (null) null; | ||
| case (?((k, v1), tl)) { | ||
| switch (find<K,W>(al2, k, keq)) { | ||
| case (null) { rec(tl)}; | ||
| case (?v2) { ?((k, v1), rec(tl)) }; | ||
| } | ||
| }; | ||
| } | ||
| }; | ||
| rec(al1) | ||
| }; | ||
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| // This operation generalizes the notion of "set union" to finite maps. | ||
| // Produces a "disjunctive image" of the two lists, where the values of | ||
| // matching keys are combined with the given binary operator. | ||
| // | ||
| // For unmatched key-value pairs, the operator is still applied to | ||
| // create the value in the image. To accomodate these various | ||
| // situations, the operator accepts optional values, but is never | ||
| // applied to (null, null). | ||
| // | ||
| func disj<K,V,W,X>(al1:AssocList<K,V>, | ||
| al2:AssocList<K,W>, | ||
| keq:(K,K)->Bool, | ||
| vbin:(?V,?W)->X) | ||
| : AssocList<K,X> | ||
| { | ||
| func rec1(al1:AssocList<K,V>) : AssocList<K,X> = { | ||
| switch al1 { | ||
| case (null) { | ||
| func rec2(al2:AssocList<K,W>) : AssocList<K,X> = { | ||
| switch al2 { | ||
| case (null) null; | ||
| case (?((k, v2), tl)) { | ||
| switch (find<K,V>(al1, k, keq)) { | ||
| case (null) { ?((k, vbin(null, ?v2)), rec2(tl)) }; | ||
| case (?v1) { ?((k, vbin(?v1, ?v2)), rec2(tl)) }; | ||
| } | ||
| }; | ||
| } | ||
| }; | ||
| rec2(al2) | ||
| }; | ||
| case (?((k, v1), tl)) { | ||
| switch (find<K,W>(al2, k, keq)) { | ||
| case (null) { ?((k, vbin(?v1, null)), rec1(tl)) }; | ||
| case (?v2) { /* handled above */ rec1(tl) }; | ||
| } | ||
| }; | ||
| } | ||
| }; | ||
| rec1(al1) | ||
| }; | ||
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| // This operation generalizes the notion of "set intersection" to | ||
| // finite maps. Produces a "conjuctive image" of the two lists, where | ||
| // the values of matching keys are combined with the given binary | ||
| // operator, and unmatched key-value pairs are not present in the output. | ||
| // | ||
| func conj<K,V,W,X>(al1 : AssocList<K,V>, | ||
| al2:AssocList<K,W>, | ||
| keq:(K,K)->Bool, | ||
| vbin:(V,W)->X) | ||
| : AssocList<K,X> | ||
| { | ||
| func rec(al1:AssocList<K,V>) : AssocList<K,X> = { | ||
| switch al1 { | ||
| case (null) { null }; | ||
| case (?((k, v1), tl)) { | ||
| switch (find<K,W>(al2, k, keq)) { | ||
| case (null) { rec(tl) }; | ||
| case (?v2) { ?((k, vbin(v1, v2)), rec(tl)) }; | ||
| } | ||
| }; | ||
| } | ||
| }; | ||
| rec(al1) | ||
| }; | ||
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| func fold<K,V,X>(al:AssocList<K,V>, | ||
| nil:X, | ||
| cons:(K,V,X)->X) | ||
| : X | ||
| { | ||
| func rec(al:List<(K,V)>) : X = { | ||
| switch al { | ||
| case null nil; | ||
| case (?((k,v),t)) { cons(k, v, rec(t)) }; | ||
| } | ||
| }; | ||
| rec(al) | ||
| }; | ||
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| }; | ||
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$(OUTDIR)should be added as order-only prerequisite. For other targets too.There was a problem hiding this comment.
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OK, good point.
I fix this once @nomeata and I settle on the other changes to the Makefile; he has another PR open for the strings defined above.