diff --git a/src/BioSequences.jl b/src/BioSequences.jl
index 111d33b1..c17599b7 100644
--- a/src/BioSequences.jl
+++ b/src/BioSequences.jl
@@ -202,6 +202,9 @@ import Twiddle: enumerate_nibbles,
     repeatpattern
 using Random
 
+const SeqLike = Union{AbstractVector, AbstractString}
+const ASCIILike = Union{String, SubString{String}}
+
 include("alphabet.jl")
 
 # Load the bit-twiddling internals that optimised BioSequences methods depend on.
diff --git a/src/alphabet.jl b/src/alphabet.jl
index 06b7ffa6..06279a18 100644
--- a/src/alphabet.jl
+++ b/src/alphabet.jl
@@ -85,7 +85,9 @@ iscomplete(A::Alphabet) = Val(length(symbols(A)) === 1 << bits_per_symbol(A))
 Encode BioSymbol `S` to an internal representation using an `Alphabet`.
 This decoding is checked to enforce valid data element.
 """
-function encode end
+function encode(A::Alphabet, x)
+    @something tryencode(A, x) throw(EncodeError(A, x))
+end
 
 struct EncodeError{A<:Alphabet,T} <: Exception
     val::T
@@ -167,11 +169,11 @@ for A in (DNAAlphabet, RNAAlphabet)
     @eval begin
 
 	    # 2-bit encoding
-        @inline function encode(::$(A){2}, nt::$(T))
+        @inline function tryencode(::$(A){2}, nt::$(T))
             if count_ones(nt) != 1 || !isvalid(nt)
-                throw(EncodeError($(A){2}(), nt))
+                return nothing
             end
-            return convert(UInt, @inbounds twobitnucs[reinterpret(UInt8, nt) + 0x01])
+            convert(UInt, @inbounds twobitnucs[reinterpret(UInt8, nt) + 0x01])
         end
 
         @inline function decode(::$(A){2}, x::UInt)
@@ -181,11 +183,8 @@ for A in (DNAAlphabet, RNAAlphabet)
 	    @inline decode(::$(A){2}, x::Unsigned) = decode($(A){2}(), UInt(x))
 
         # 4-bit encoding
-        @inline function encode(::$(A){4}, nt::$(T))
-            if !isvalid(nt)
-                throw(EncodeError($(A){4}(), nt))
-            end
-            return convert(UInt, reinterpret(UInt8, nt))
+        @inline function tryencode(::$(A){4}, nt::$(T))
+            isvalid(nt) ? convert(UInt, reinterpret(UInt8, nt)) : nothing
         end
 
         @inline function decode(::$(A){4}, x::UInt)
@@ -220,11 +219,11 @@ function symbols(::AminoAcidAlphabet)
     AA_Y, AA_V, AA_O, AA_U, AA_B, AA_J, AA_Z, AA_X, AA_Term, AA_Gap)
 end
 
-@inline function encode(::AminoAcidAlphabet, aa::AminoAcid)
+@inline function tryencode(::AminoAcidAlphabet, aa::AminoAcid)
     if reinterpret(UInt8, aa) > reinterpret(UInt8, AA_Gap)
-        throw(EncodeError(AminoAcidAlphabet(), aa))
+        return nothing
     end
-    return convert(UInt, reinterpret(UInt8, aa))
+    convert(UInt, reinterpret(UInt8, aa))
 end
 
 @inline function decode(::AminoAcidAlphabet, x::UInt)
diff --git a/src/longsequences/constructors.jl b/src/longsequences/constructors.jl
index abdd2f94..80d01858 100644
--- a/src/longsequences/constructors.jl
+++ b/src/longsequences/constructors.jl
@@ -60,20 +60,8 @@ function (::Type{T})(seq::LongSequence{<:NucleicAcidAlphabet{N}}) where
 end
 
 # Constructors from strings
-function LongSequence{A}(s::Union{String, SubString{String}}) where {A<:Alphabet}
-    return LongSequence{A}(s, codetype(A()))
-end
-
-# Generic method for String/Substring.
-function LongSequence{A}(s::Union{String, SubString{String}}, ::AlphabetCode) where {A<:Alphabet}
-    len = length(s)
-    seq = LongSequence{A}(undef, len)
-    return copyto!(seq, 1, s, 1, len)
-end
-
-function LongSequence{A}(s::Union{String, SubString{String}}, ::AsciiAlphabet) where {A<:Alphabet}
-    seq = LongSequence{A}(undef, ncodeunits(s))
-    return encode_chunks!(seq, 1, codeunits(s), 1, ncodeunits(s))
+function LongSequence{A}(s::AbstractString) where {A <: Alphabet}
+    return parse(LongSequence{A}, s)
 end
 
 function LongSequence{A}(
@@ -85,4 +73,34 @@ function LongSequence{A}(
     return copyto!(seq, 1, src, first(part), len)
 end
 
-Base.parse(::Type{LongSequence{A}}, seq::AbstractString) where A = LongSequence{A}(seq)
\ No newline at end of file
+Base.parse(::Type{T}, s::AbstractString) where {T <: LongSequence} = parse(T, String(s))
+
+function Base.parse(T::Type{LongSequence{A}}, s::ASCIILike) where {A<:Alphabet}
+    C = codetype(A())
+    src = C isa AsciiAlphabet ? codeunits(s) : s
+    n = _tryparse(T, s, C)
+    if n isa Int
+        throw_encode_error(A(), src, n)
+    else
+        n
+    end
+end
+
+Base.tryparse(::Type{T}, s::AbstractString) where {T <: LongSequence} = tryparse(T, String(s))
+
+function Base.tryparse(::Type{LongSequence{A}}, s::ASCIILike) where {A <: Alphabet}
+    n = _tryparse(LongSequence{A}, s, codetype(A()))
+    n isa Int ? nothing : n
+end
+
+function _tryparse(::Type{LongSequence{A}}, s::ASCIILike, ::AlphabetCode) where {A<:Alphabet}
+    len = length(s)
+    seq = LongSequence{A}(undef, len)
+    # TODO!
+    return copyto!(seq, 1, s, 1, len)
+end
+
+function _tryparse(::Type{LongSequence{A}}, s::ASCIILike, ::AsciiAlphabet) where {A<:Alphabet}
+    seq = LongSequence{A}(undef, ncodeunits(s))
+    try_encode_chunks!(seq, 1, codeunits(s), 1, ncodeunits(s))
+end
\ No newline at end of file
diff --git a/src/longsequences/copying.jl b/src/longsequences/copying.jl
index b98e0360..d18a73e6 100644
--- a/src/longsequences/copying.jl
+++ b/src/longsequences/copying.jl
@@ -107,8 +107,6 @@ function _copyto!(dst::SeqOrView{A}, doff::Integer,
 end
 
 #########
-const SeqLike = Union{AbstractVector, AbstractString}
-const ASCIILike = Union{String, SubString{String}}
 
 """
     copy!(dst::LongSequence, src)
@@ -167,7 +165,12 @@ end
     @assert false "Expected error in encoding"
 end
 
-@inline function encode_chunk(A::Alphabet, src::AbstractArray{UInt8}, soff::Integer, N::Integer)
+@inline function encode_chunk(
+    A::Alphabet,
+    src::AbstractArray{UInt8},
+    soff::Integer,
+    N::Integer
+)::Union{UInt64, Int}
     chunk = zero(UInt64)
     check = 0x00
     @inbounds for i in 1:N
@@ -175,26 +178,51 @@ end
         check |= enc
         chunk |= UInt64(enc) << (bits_per_symbol(A) * (i-1))
     end
-    check & 0x80 == 0x00 || throw_encode_error(A, src, soff)
-    return chunk
+    check & 0x80 == 0x00 || return Int(soff)::Int
+    return chunk::UInt64
 end
 
 # Use this for AsiiAlphabet alphabets only, internal use only, no boundschecks.
 # This is preferential to `copyto!` if none of the sequence's original content
 # needs to be kept, since this is faster.
-function encode_chunks!(dst::SeqOrView{A}, startindex::Integer, src::AbstractVector{UInt8},
-                        soff::Integer, N::Integer) where {A <: Alphabet}
+function try_encode_chunks!(
+    dst::SeqOrView{A},
+    startindex::Integer,
+    src::AbstractVector{UInt8},
+    soff::Integer,
+    N::Integer
+)::Union{Int, SeqOrView} where {A <: Alphabet}
     chunks, rest = divrem(N, symbols_per_data_element(dst))
     @inbounds for i in startindex:startindex+chunks-1
-        dst.data[i] = encode_chunk(A(), src, soff, symbols_per_data_element(dst))
+        chunk = encode_chunk(A(), src, soff, symbols_per_data_element(dst))
+        if chunk isa Int
+            return chunk
+        else
+            dst.data[i] = chunk
+        end
         soff += symbols_per_data_element(dst)
     end
     @inbounds if !iszero(rest)
-        dst.data[startindex+chunks] = encode_chunk(A(), src, soff, rest)
+        chunk = encode_chunk(A(), src, soff, rest)
+        if chunk isa Int
+            return chunk
+        else
+            dst.data[startindex+chunks] = chunk
+        end
     end
     return dst
 end
 
+function encode_chunks!(dst::SeqOrView{A},
+    startindex::Integer,
+    src::AbstractVector{UInt8},
+    soff::Integer,
+    N::Integer
+)::SeqOrView where {A <: Alphabet}
+    s = try_encode_chunks!(dst, startindex, src, soff, N)
+    s isa Int ? throw_encode_error(A(), src, s) : s
+end
+
 #########
 
 # Two-argument method