original.name="ConstrainedList_Valid_11"
======
>>> main.whiley
type state is ({
    int[] input,
    int pos
} _this)
where (_this.pos >= 0) && (_this.pos <= |_this.input|)

public function isLetter(int c) -> bool:
    return ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z')

function f(state st) -> int:
    if st.pos < |st.input|:
        if isLetter(st.input[st.pos]):
            return st.input[st.pos]
    return ' '

public export method test() :
    assume f({input: "hello", pos: 0}) == 104

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